Re: something of interest
Here is something of interest I wrote to a response to another forum that might be of interest here.
If I went with the identical lamp that's in this
fixture, are you saying that it would be a more "brown appearing lamp"? You made that reference but am wondering if there is a lamp that is a more white appearing lamp as well. In the application that I will be using these lights, the distance to the
stage is approvimately 20 feet. I personally think that 575w is a bunch, although I am planning on hooking it up to a 600w per
channel dim pack. Is it better to have the wattage there if needed, and just dim it when not? That sounds logical to me
A specific answer to your question would be no, installing an identical lamp to one that’s in the
fixture will not appear more brown, it will appear the same. Answering what I think is your real question, installing the same
HPL 575w/115vX lamp in the
fixture and dimming it down will make that lamp appear more brown than installing a lesser wattage lamp and not dimming it or only dimming it slightly. Amber
Shift. Get out a
stage lighting
book, most will
cover the subject. A lamp operating at or over it’s rated
voltage will appear more white than one that is dimmed. With
color temperature, distance has little
effect on the appearance of the light’s color. The color of a beam at 20' is the same as the color of a 100' beam. It’s output that drops the further away you get. Output of a dimmed lamp verses that of a lesser wattage lamp is effected the same by distance. Light is light no matter if it comes from a
dimmer or not.
The major choices you need to figure is lamp life, maximum output desired and cost effectiveness. If your fixtures need to give out as much light as possible, and you can budget for shorter life lamps, those are the ones to choose. If lamp life is your major consideration over output, than longer life lamps should be chosen. If you need long life lamps but at a certain amount of
intensity, than you would need to use a higher wattage lamp to achieve the same
intensity. If you need less
intensity, and only have so much wattage available, than you will have to sacrifice life for output. If you plan to leave your lights dimmed, than they will be further extended in life but will loose the
color temperature that’s the major selling
point of the lamp. In that case, installing a lower wattage less life lamp in your
fixture will be better to preserve the
color temperature. Such lamps will cost more money in the long run to keep replacing, but will save money in size of dimmers needed to operate them and energy costs. Lots of things to consider.
Here is a much more detailed description of what’s going on. If you can follow it, you will learn a lot about lamps and the factors that go into design of them. Not all about them, I’m even still learning, but a good part specifically about
color temperature and life. Many more details yet.
Lamp color temperatures, wattages and life or at least small tidbits of the equation.
A lamp that appears more brown is an observation of it having a lower
color temperature than your mental reference color appearance of what a light should look like by memory or visually in comparison to other beams of light near it. It’s subjective unless verified by a light
meter or individual lamp specification test data. Color appearance is dependant upon many things such as the angle you view it at especially in reference angle to other beams of light, surface
reflection and coating the beam of light is bouncing off of, differences between beams in similar areas, operating
voltage and
dimmer intensity - amber
shift,
fixture efficiency and
lens characteristics, age of lamp with some lamps, and design values of it,
etc.
In other words, operating a 115v lamp at 120v will be causing the
filament to heat up more and thus give off a slight increase in
color temperature which is directly related to the temperature the
filament is operating at up to the
filament’s maximum usable temperature. Beyond that, you can also use color boosting filters at a slight loss of light to boost the
color temperature of the lamp. However, since lenses and reflectors kind of filter a beam of light while it bounces off or passes
thru them, this will also
effect the beam’s color and output dependant upon their efficiency or purity.
Color temperature unlike output is not effected by distance as long as there is not atmospheric filters involved in the light.
Color temperature is also related to light output in it’s spectral graph of the emissions from the burning source. The spectral graph as opposed to the spectral curve is a slightly more accurate telling of lamp specific output in that it shows spikes of light output at certain nanometers of wavelength as opposed to rounding them out into a more general curve of output with the average output being what
color temperature the lamp is rated for burning at.
Burn salt, and it gives off a certain
color temperature in general -
sodium vapor lamps, but more specifically, it gives off a wide range of colors both visible and not, corresponding to spikes in output in certain areas of
color temperature as plotted on a spectral graph. (The same type of thing astronomers use to get data on distant stars.) The pressure,
dichroic coatings and gas fillings of a lamp have a large factor in an
incandescent lamp on what
color temperature they burn at, or what spikes that lamp’s spectral graph has it’s spikes at. A
incandescent vacuum lamp is going to have a lower
color temperature than a Nitrogen filled lamp, and that’s less than a
Xenon lamp because with the pressure, those chemicals allow the
filament to burn hotter without burning up. They also
effect certain parts of the light as plotted by adding their own composition when burning up to that of the spectral graph for a normal
filament. Krypton for instance would have more spikes in the green area than Xenon. But this part is my assumption because the gas is not really burning. It is however to some degree incandessing and filtering the light providing and
blocking certain wavelengths of otherwise normal
tungsten incandescence.
Other factors such as
halogen gas or
dichroic coatings will also
effect the operating temperature of the
filament in allowing it to safely operate hotter.
Halogen because it is replenishing the
filament by re-depositing what burns up and falls off back on the
filament so it can burn again once cool. The lamp is able to operate at the higher temperature in burning itself up but being re-supplied to a
point as long as that re-depositing of the
filament is even and not just in certain areas of it. It’s not perfect and the lamp will eventually have a part of the
filament not having enough mass to resist breaking, but it in general extends lamp life given it’s operating at the right temperature. A
dichroic lamp coating such as on a
HPL/HX-600 lamp, takes the IR heat out of the beam and reflects it back to the
filament letting it operate at a higher temperature by convection than applied
voltage. In other words, it is getting it’s source of heat not only from the
voltage applied to it, but it is also heating up by getting heat reflected from the light it is putting out, back on the part that’s generating the heat making it heat up more yet above the
voltage applied. Since this will cause the
filament to deteriorate faster, there had to be improvements in the
filament design and
halogen cycle to implement this.
A 500w
Halogen lamp in general is as bright as a 750w
incandescent lamp, as is bright as a 375w
Dichroic Halogen lamp in the most
broad sense. It’s also going to have a higher
color temperature due to the improvements because the
filament is allowed to burn brighter - at least in parts of it’s spectral spikes such as on the higher wavelengths. A
Halogen lamp and a
Dichroic Halogen lamp might be rated for the same
color temperature, but because of the heat applied to the
filament, a larger portion of it’s average spikes will be in the higher wavelengths. Both lamps have the same average
color temperature in reference to the range they burn at, but the
Dichroic lamp is going to have a larger percentage of spikes in the higher spectrum. Thus lamps rated for a
color temperature based upon a spectral curve is misleading in actual color of light given out especially when not corrected for in the case of a 115v lamp it operated over
voltage.
In specific reference to your lamps
HPL 575w/115v Extended life lamps, the individual
color temperature or color appearance of a
HPL lamp in a S-4
fixture (also dependant upon it’s type of
reflector because if I remember right,
ETC makes two types of
reflector at least for the
PAR cans,) is very much dependant upon the brand of the lamp and what mix or chemicals are used in it’s makeup. This data is published in the lamp specifications for each individual lamp along with life and luminous output. These published specifications change from year to year because how a lamp is made or what percentages of gas or types of materials used for it change year to year and lot number to lot number. One brand to another, due to differing manufacturing processes, materials and mixtures, output will be different in many cases be very noticeable such as the case between brands of HMI1200w/GS lamps and refrenced in the manufacturer data or at least in the spectral spikes that are a little harder to see but are still there and present many times as you
gel or dim the lamps.
Short of using a calibrated light
meter on each brand and type of lamp, the best way to tell what the
color temperature is going to be of specific brands of lamps is by using the published data on them. Remember how many factors go into what a
color temperature appears to be thus how in-accurate it depending upon what you perceive should be in the color, such as efficiency of the
fixture and even where you stand. Differences in brand to your eyes in comparing lamps unless drastic in difference such as say over 1,000°K is hard to tell. That said, as I inferred, the Ushio lamps by specification have better
color temperature in general than Osram
HPL or GLA lamps. That’s based upon the data each company has provided at least this year and it’s probably going to change. Will you be able to tell the difference between even a GE and Philips lamp with only a few hundred degrees difference in
color temperature (taken as a example and not specific lamps) given the data provided is accurate to the lot number of lamp you use? Probably not with your eyes. However, once such lamps are filtered with the same color, since individual brands of lamp have a different actual
color temperature and thus different spectral graph spikes, they will
effect the
gel or even paint on a
stage differently. A lamp with a red
gel such as say a RX27 will react differently with a 2,950°K lamp than with a 3,050°K lamp in general and specifically with spikes of light on the lower end of the spectrum.
Wiko/Eiko/SoLux, Philips, Osram/Sylvania, GE/Thorn/Koto, Ushio/Reflekto as the major brands of
bulb many times if
ANSI coded will have similar outputs, life and
color temperature on paper, or if accurate for the
current catalog, slightly different outputs, it all depends upon the brand and lamps change year to year or lot to lot.
How they rate their bulbs can also be wishful thinking, inaccuracies in the test data, different mixtures or materials year to year, even hour to hour, or even atmospheric or locution differences on the test facilities. Than there is what is being tested such as initial verses mean output or in life what they
call the average life of a
bulb, be it 40% burning out after a period of time, 10% burning out, 50%,
etc and how large that sample was, across how many lot numbers of the test sample and how controlled the experiment is, or how many they
thru out. It can also be rated by how many lamps in that sample blew out or what percentage of the expected life the lamps blew out at. For instance, in Osram - Technology and Application,
Tungsten Halogen Low
Voltage Lamps Photo Optics p.32
“The lamp specified for
tungsten halogen Low
Voltage lamps is based upon defined “average lamp life.” This is the time after which, on a statistical average, half of a not too small number of lamps fail. “Fail” means that the
filament burns out. To be on the safe side, lamp manufacturers as a rule set the design value slightly above the promised “average lamp life.” This modifies the above definition to the time after which, on statistical average, half the lamps may fail. The lamp life distribution of individual lamps in a group approximately follows a Gaussian bell-shaped curvve. Lamp manufacturers have the following to say about the width of this curve: individual lamp life is at least 70% of average lamp life. If for example the average lamp life is 100 hours, every lamp will last for at least 70 hours, except for premature failures - the black sheep of mass production which can never be entirely avoided. A mandatary percentage limit laid down internationally - the AQL - is specified for these premature failures (AQL stands for “Accepted Quality
Level” and is part of a comprehensive statistical quality
system in common use internationally, see DIN 40080) the AQL value varies for different groups of lamps (general lighting service, photo-optic applications,
etc.) The
tungsten halogen LV lamps under consideration here normally have an AQL of 6.5 which means in
practical terms that 6.5% of the lamps in a sufficiently large random sample do not have to achieve the individual lamp life. In accordance with the lamp life definition, they may fail shortly after being switched on for the first time or, as in the above example, after 69 hours.”
Lots of differences between brands in addition to differing materials and quality of workmanship going into individual lamps that would be factors both in specified data and spectral graph output. Lots of quality control or AQL levels that can be used. In general, once you get a brand of lamp, stick with it for similar fixtures doing the same work. Differing materials making up the lamp will even react to
voltage applied to it differently. Granted most of what I am writing is in the most finite of measurements on the data. Differences between
HPL lamps can be large by using the specified numbers even if the actual visual differences are possibly too small to be seen. Differences between say FLK lamps in general on paper are not noticeable and only the spectral curve and materials and quality of the lamp have effects that can be judged but almost certainly not noticed unless you are dimming them or filtering them.
By the way, a Osram
HPL 575w/C lamp has a very slightly larger
color temperature than a Ushio lamp by the specifications, but the same is not the case in the
HPL 375w/C lamp. For me at least, the lamp and it’s
heat sink on the Osram lamp don’t have the bond of a Ushio lamp to it’s
heat sink and the Osram lamp frequently pulls out of the
heat sink. That’s why I don’t buy them. even at a lower cost, I don’t even consider Wiko lamps for S-4 fixtures. Sometimes, it’s not lamp data that is a factor in buying lamps, in the case of a 2Kw CYX lamp, the shipping boxes that package GE and Philips lamps doesn’t support the
bulb well enough for it to survive being bounced around in the back of a truck as a spare lamp well enough for me to buy them even if more in output. Ushio and Osram CYX lamps hold up better to transport and thus I buy them. For me, the Osram lamp is cheaper than the Ushio lamp so it’s my primary lamp in spite of any loss in output. Is the packaging of a Ushio
HPL lamp better than that of a GE or Osram lamp, good debate, but not much different in quality once it does some travel or gets wet.
Try lighting a bloody scene on
stage with a
incandescent plano-convex
fixture such as a Bantam Super Spot, than with a S-4
fixture. You can even use a radial mounted
Altman #360 for this. Use the same
voltage, percentage of
dimmer, and say a 750w lamp in the Plano
Convex verses a 375w lamp in the
ETC fixture. Not only especially with
gel will each beam of light appear much different, but the color of the blood, and it’s sparkle or pop will be totally different. Now start to dim them. As you dim a lamp, you get “amber
shift” going on. That’s the result of the lamp’s
filament burning cooler and not putting out as much light, but also the
filament’s temperature not burning at the same
color temperature or heat from the
voltage, thus it drops as you dim the lamp. There will be a different dimming curve between types of lamps that can be noticeable. In general, when you dim a lamp however, it will be effected by amber
shift. That’s why it is better to put a 375w S-4 lamp into a
fixture as opposed to leaving it on a
dimmer with a 575w lamp to provide the same
intensity while dimmed. Lamp might last longer, the
intensity might be the same, but the output in color is going to be crap - like lighting the
stage with candles. Since different lamps have different places they
spike in color - or groupings of color’s the
filament is burning at, a lamp when dimmed will
drop in output and
color temperature following that graph with the spikes that are largest lingering the longest in the light beam still present in the dimmed beam of light. That’s dependant upon the chemical fillers making up the lamp and what
color temperature or heat it’s burning at. After a certain
point, all
filament lamps will no longer have the benefits of the filler boosting
color temperature and will burn similar. A
HPL lamp with a
dichroic coating reflecting heat back to the
filament, and having a
halogen (Bromine or Iodine) and Krypton or Xenon filler will have a different normal operating
color temperature than a lamp having a nitrogen/argon filler because it cannot burn as hot in suppressing the rate of vaporization, given the same wattage or resistance present in the
filament. It’s spikes thus as you
drop the
power into the
filament will be highly different with the
HPL lamp lingering longer in a brighter/more white output than with a normal
halogen or
incandescent lamp, though both at some
point will have similar outputs at lower
dimmer ratios. Thus, in at least my theory, a
HPL/HX-600 lamp will have less problems with amber
shift up to a
point when those advantages will rapidly
drop off.
(Osram - Technology and Application,
Tungsten Halogen Low
Voltage Lamps Photo Optics.) “The reduced rate of vaporization of the
tungsten can either be used to increase lamp life or - if the life remains the same - to increase the
luminous efficacy and the
color temperature by raising the temperature of the
tungsten. In both cases, using the standard krypton lamp as a starting
point, the
filament dimensions have to be recalculated and the lamp filling modified.
Luminous efficacy can be increased by about 5-10% with the “Xenon
Effect”, which corresponds to a
color temperature increase of about 100K. Xenophot technology can only be used for low-voltage lamps. In high-voltage lamps the lower ionizing energy of Xenon would lead to electrical discharge in the lamp
bulb.”
That resistance in the
filament is the wattage of the
filament as modified by the
voltage it is designed to operate at. The larger the
voltage, the larger the
filament needs to be to carry the
current safely where life and cold starting is concerned amongst other factors. The larger the
filament, the longer it’s going when dimmed to retain it’s heat and thus
color temperature for the initial dimming up or down. In many cases, that’s coming close to the rate your eyes adjust for the
drop in
color temperature or output without you noticing it. The larger the
filament, the less resistant the materials comparatively will be to the flow of electricity due to the mass of the
wire radiating the same amount of heat. It’s still giving off the same amount of heat, just doing less work to do so and thus burning up less.
Another way of controlling resistance in the
wire is by changing the percentage of
tungsten to other materials in it. A long life lamp can have the same size of
filament wire, but have longer lasting - more resistant to heat materials making it up that incandess a little less or even a higher percentage of
halogen in the gas or be operating at a higher temperature allowing the
halogen cycle to operate more effectively. Differences in how the
bulb is designed or the gas flows within the lamp will also
effect this. With any of these methods the long life lamp in general will have less output, but the same
color temperature in most instances, but you can retain the same output and life by adjusting the
color temperature the
filament burns at. There are three primary factors life, output and
color temperature to a lamp given it’s resistance and
voltage by design are the same. Adjusting any of them is a question of fillers, coatings,
voltage,
filament composition and winding of that
filament. A
filament designed for a high
color temperature, and high
voltage such as 125v will when at a lesser
voltage have a similar
color temperature to a lamp designed for 115v operation but more life when operated under
voltage given the same life
rating at the start. The only thing that will
drop is luminous output. On the other
hand, when you operate a 120v lamp rated exactly the same as a 115v lamp at 115v, it’s going to have a longer rated life, but less
color temperature and output. The 120v lamp will appear less bright in both color and
intensity. The main difference between 130v and 120v
incandescent lamps in a household
fixture. The larger
filament will also be more resistant to
voltage spikes and cold starting in-rush currents effecting the
filament by making it operate at a higher
voltage and temperature if only for a few moments.
Since filaments have different compositions, in addition to the fillers, closeness of
filament wires to each other having a thermal
effect on them, and coatings on the lamps, they on a spectral graph will have differing spikes on the chart brand to brand and type to type. A long life lamp will have differing dimming characteristics than a high output lamp due to what’s burning inside of it and what spikes they have. Also if the lamp is say already a higher
voltage lamp that’s operating on a lesser
voltage, than it will tend to more rapidly be effected by amber
shift than one that is operating at it’s peak output because it’s already not at it’s peak values and some parts of the range of light are already not there.
All of that said, when you operate a 115v lamp over it’s rated
voltage, such as on a
HPL lamp at 120 or more realistically 117v, than it’s going to have a higher
color temperature than it’s rated and published
color temperature.
HPL/HX-600 lamps appear more blue than other lamps in older
stage lighting fixtures in part due to
fixture efficiency. The design
color temperature is usually about the same as with 120v lamps, (the
color temperature difference between a EHD lamp and a
HPL lamp is 250°K and that’s not noticeable in theory,) but the
voltage is boosting the
color temperature to make it look different in a factor of 2% color for 5% in volts (making it seem as if the lamp had a 120v. 3,770°K
color temperature instead of a 115v, 3,250°K
color temperature, or 2,950°K
color temperature of a EHD lamp) in addition to it’s differing spectral spikes from operating at a higher
filament temperature, while sacrificing lamp life at operating over
voltage. (That’s 50% less life when using a 115v
HPL high output lamp on a 120v
circuit or 150 hours without dimming. Don’t believe me, check the math, for every 1% of difference in supply
voltage, life is effected by 12%. Large increase in
color temperature not to mention actual output. Remember also that the actual amount of time such lamps are on is not much especially when dimmed down to voltages below 115v which go back to extending their life, plus
line voltage after
voltage drop is usually much less than the calculated 120v.)
HPL/HX-600 lamps operated over
voltage and with their various improvements are kind of similar to car engines with a nitro boost. It’s the same basic engine though probably improved for the best output, but that nitro boost makes it go faster and burn out the engine faster as a secondary result. A
HPL lamp appears brighter in
color temperature and has more output much due to the
voltage. A
HPL 575w lamp operated over
voltage, and with it’s improved
dichroic coating and gas mixtures, puts out as much light (17,208.333 Lum/120v out of a 16,520 Lum lamp) as a average between a EHG and EHF 750w Quartz lamp. More than the EHG (usually 15,400 Lum) with it’s longer life, and less than a 750w EHF (Usually 20,400 Lum) with it’s similar life to that of a
HPL lamp when at differing design voltages. Thus, a
HPL 575w lamp, in a higher and more efficient
fixture puts out about as much light as a 750w lamp, but in the higher efficiency
fixture might even put out slightly more say 800w worth of
halogen light because the light is collected and focused more efficiently. That 800w figure is also based upon how the light appears. Since as you raise the
voltage that 4%, your
color temperature also goes up, the light is going to appear more blue especially with better lenses on a
ETC fixture in addition to differences in the lamp itself. A lamp operating at a higher
color temperature seems to be brighter even if the same or less in actual lumens coming out of the
fixture. It appears to be brighter and we perceive it to have more luminous output because of it. However actual output in many cases can be less such as on a multi-vapor lamp. It’s usually the case that a lamp having a larger
color temperature will have less of a
CRI rating. That’s the case even if the actual lamp has the same luminous output on paper. It’s a question of how natural that light looks in being useful verses just plain how bright it appears.
The maximum burning temperature of a average
filament is about 3,550°K (3383°C) when operated at it’s rated
voltage. There are some
incandescent lamps out there that burn at about that
color temperature without using any filters to boost it. However any time you put a
filament at it’s maximum burning temperature, or the closer you get to it, the faster it will burn up or larger chance it will be adversely effected by variations in
voltage applied to it. Normal maximum
color temperature of
stage and studio bulbs is between 2,800°K and 3,200°K which leaves somewhere around 20 Volts (my figure) of margin of error before the
filament burns itself up too rapidly for it to be used. A better figure would be using a 10% maximum variation in over-Voltage. For a
HPL lamp designed for a 115v lamp, you don’t want to operate it at over 126.5v for semi extended use or 131.43v (14%) for a
voltage spike. Osram says in their below
book, start up lamp
filament resistance can be as much as 20 times less than operating resistance, and most lamps are designed for a start up
voltage of 108%. With every 3 lumens per
watt applied to the lamp,
color temperature changes by 100K. That’s a
base way of determining
color temperature when not given. Remember this figure for special effects and low
voltage lights.
(Osram -
Tungsten Halogen Low
Voltage Lamps Photo Optics p.21 as referenced from IES Lighting Handbook & The Science of Color as a refrence) “The following variables can be related in a fixed formula for
incandescent lamps.
- Luminous flux
-
Luminous efficacy
-
Color temperature
- Electrical
voltage
- Electrical
current
- Electrical
power consumption
In non-tungsten
halogen lamps, lamp life can also be added to this list as it is only determined by the physically measurable evaporation rate of the
tungsten filament. In
tungsten-halogen lamps, lamp life is also affected by the chemistry of the
tungsten halogen cycle. A fixed mathematical relationship with the above variables therefore only exists in a small, well-defined range.
The mutual dependence of these variables can be shown very clearly in a diagram id the
deviation from the rated lamp
voltage us used as the abscissa.
The following rule of thumb can be derived:
A 5% change in
voltage applied to the lamp results in
- halving or doubling the lamp life
- a 15% change in luminous flux
- an 8% change in
power
- a 3% change in
current
- a 2% change in
color temperature
The limitation described above applies to lamp life. It must also be noted that increasing the
voltage may in some circumstances not be permissible, depending on the design of the lamp; if it causes the
tungsten filament to reach its melting
point the lamp will burn out.”
Review of this only small portion of the subject as I understand it: A long life lamp will last longer than a high output lamp in exchange for output or real light coming out of it, or exchange
color temperature for life and it has to be one of the two if you don’t change the
voltage or wattage given the same fillers.
The long life lamp should react just slightly different under a
dimmer or over
voltage than a high output lamp also due to the differing materials making it up as plotted on a spectral graph.
Such lamps as a
HPL lamp are more efficient by design and fixtures they are used in than
halogen lamps used in older fixtures, just as
halogen fixtures were a vast improvement over
incandescent sources.
Any
filament lamp is limited in it’s maximum
color temperature by the
filament itself and what pressure or gasses surround it preventing it from evaporating or burning up too rapidly which is also effected by
voltage applied to it in addition to other things such as frequency.
When you operate a lamp at too high a
voltage, it gets really bright but goes
super nova just as fast. Otherwise in the case of a
HPL lamp, it has more
color temperature and output but less life. A
HPL 575w/115v lamp will look very different than a
HPL 575w/120v lamp when operated at the same
voltage no matter what it is. Those differences are enough to notice even though there is only a 4% change in
voltage applied to it and that on a
dimmer usually is not enough to notice in difference between the same lamps.
A lamp when dimmed is going to have amber
shift effecting it and will provide light corresponding to the spikes on the output graph up to a
point when special gasses, proximity to other parts of the
filament or
dichroic coatings stop effecting the output and it will than
return to normal
incandescent output. Those spikes on a dimmed lamp will make it linger in certain ranges of spectral color and appear different, making say a
HPL lamp look different on a
dimmer look different in
color temperature than a lesser wattage lamp not dimmed. It is going to have amber
shift and loose much of the usable light in it’s full range of colors, but it will linger at certain points differently.
A lamp with differing compositions of the
filament, or what is “doped” into it’s make up will also have slightly differing spectral spikes as would a larger
filament lamp when dimmed to a
point that it is operating at the same temperature. Tin will have a different burning
spike pattern than that of a copper doping given that’s what’s used.
A dimmed lamp in comparison to a lamp operating at it’s rated
voltage but at a smaller wattage will have about the same luminous output at some
point in dimming no matter what the
color temperature, and both will be effected exactly the same by the
law of squares or law of inverse squares which ever applies the further away from the
fixture you get.
The
color temperature and life of that dimmed lamp will be inversely effected by dimming to life but less so effected than Lumionous Output will be in going down as the lamp is dimmed. This is also effected by the types of chemicals, proximity of the
filament wires to each other or
thickness of the
wire or other factors such as pressure, chemicals used and
dichroic coatings as they relate to
filament heat at
voltage to the lack of benefits such things offer. At some
point, a lamp given
current is just heating the
wire and not incandessing, at some
point before that, no matter what chemical or pressure you are using to allow for a higher burning temperature of the
filament, the lamp is acting as if a normal
incandescent lamp in life and output in a
broad sense even with spikes in spectral output considered.
When you have a need for a lower
intensity on a source and don’t need to go above it, it is better to perhaps dim it very slightly to extend life, but always go for the lower wattage lamp that is operating at peak
color temperature because the actual radiation of the lamp in the visable spectrum of light will be more full in all areas of light and operating at it’s design peak.
If you only need 10,500 Lumens out of a
fixture, rather than dimming a 575w lamp to about 66%, you are better off putting a 375w lamp in the
fixture, it’s giving design
color temperature with all light present in it’s spectral graph.
Note:
HPL lamps and FLK/HX-600 series lamps are for all intensive purposes the same lamp see the GLA series of lamp that used to be able to be used for either type of
fixture. You can get a HX-400 lamp that’s going to be about the same as a HPL375, just as you can get a HX-754 or HX-800 lamp that’s going to be the same as a
HPL 750. Just a question of what
fixture it’s in and your need for output. All styles have long life variants. A Shakespeare and a
ETC S-4
fixture use those different lamps but can be expected to have similar outputs coming out of them.
Notes: (Anything without a source following it probably comes from a GE catalog especially the GE-Spectrum Catalog.)
Cand. =
Candlepower,
Candlepower is the normal
rating method of the total light output of miniature lamps. To convert this
rating to lumens multiply it by 12.57 (4 pi).
Mean
spherical candlepower MSCP is the initial mean
candlepower at the design
voltage. It is subject to manufacturing tolerances. Mean
spherical candlepower is the generally accepted method of
rating the total light output of miniature lamps.
cd =
Candela. The international
unit (SI) of luminous
intensity. The term has been retained from the early days of lighting when a standard candle of a fixed size and composition was used as a basis for evaluating the
intensity of other light sources.
Chromacity = See
Color Temperature
Color
Rendering = As a rule, artificial light should
enable the human eye to perceive colors correctly, as it would in natural
daylight. Obviously, this depends to some extent on the location and purpose for which light is required. The criterion here is the color
rendering property of a light source. This is expressed as a “general color
rendering index” (
CRI). The color
rendering index is a measure of the correspondence between the color of an object (its “selfluminous color”) and its appearance under a reference light source. To determine the
CRI values, eight test colors defined in accordance with DIN 6169 are illuminated with the reference light source and
the light source under test. The smaller the discrepance, the better the color
rendering property of the lamp tested. A light source with a
CRI value of 100 displays all colors exactly as they appear under the reference light source. The lower the
CRI value, the poorer the colors are rendered. - Osram Photo-Optic Lighting Products, 1999
Color Temperature = Originally, a term used to describe the “whiteness” of
incandescent lamp light.
Color temperature is directly related to the physical temperature of the
filament in
incandescent lamps so the Kelvin (absolute) temperature is used to describe
color temperature. For discharge lamps where no hot
filament is involved, the term “correlated
color temperature” is used to indicate that the light appears “as if” the discharge lamp is operating at a giving
color temperature. More recently, the term “chromaticity” has been used in place of
color temperature.
Chromacity is expressed either in Kelvins (K) or as “X” and “Y” coordinated on the CIE Standard Chrom-aticity Diagram. Although it may not seem sensible, a high
color temperature (K) describes a visually cooler, bluer light source. Typical color temperatures are 2,800°K (
incandescent), 3,000°K (
halogen), 4,100°K (cool white or sp41
fluorescent), and 5,000°K (daylight-simulating
fluorescent colors such as
Chroma 50 and SPX 50.
Unit of measurement: Kelvin (K) the
color temperature os a light source is defined in comparison with a “black body radiator” and plotted on what is known as the “Planckian curve.” The higher the temperature of this “black body radiator” the greater the blue component in the spectrum and the smaller the red component. An
incandescent lamp with a warm white light, for example, has a
color temperature of 2,700°K, whereas a
daylight has a
color temperature of 6,000°K. - Osram Photo-Optic Lighting Products, 1999
Light color = The light color of a lamp can be neatly defined in terms of
color temperature. There are three main categories here: warm<3,300°K, intermediate 3,300 to 5,000°K, and
daylight > 5,000°K. Despite having the same light color, lamps may have very different color
rendering properties owing to the spectral composition of the light. - Osram Photo-Optic Lighting Products, 1999
Hal =
Halogen Lamp - A short name for the
tungsten-halogen lamp.
Halogen lamps are high pressure
incandescent lamps containing
halogen gasses such as iodine or bromine which allow the filaments to be operated at higher temperatures and higher efficacies. A high-temperature chemical reaction involving
tungsten and the
halogen gas recycles evaporated particles of
tungsten back onto the
filament surface. Also called a Quartz lamp, though this is a term for the higher melting temperature glass enclosure used on
halogen lamp
HIR =
Halogen - IR Lamp.
Dichroic Lamp Coatings. G.E. designation for a new form of high-efficiency
tungsten halogen lamp. HIR lamps utilize shaped
filament tubes coated with numerous layers of materials which selectively reflect and transmit
infrared energy and light. Reflecting the
infrared back onto the
filament reduces the
power needed to keep the
filament hot.
Illuminance = The “density” of light (lumens/area) incident on a surface. Illuminance is measured in footcandles or
lux. - GE Spectrum Catalog
Illuminance = The “density” of light (lumens/area) incident on a surface. Illuminance is measured in footcandles or
lux.
A
unit of measurement:
lux (lx) illuminance E is the ratio between the luminous flux and the area to be illuminated. An illuminance of 1 lx occurs when a luminous flux of 1lumen is evenly distributed over an area of one square
meter. - Osram Photo-Optic Lighting Products, 1999
Lamps with Blue
Dichroic Reflectors: Lamps with Semi-Clear Blue Reflectors reflect less unwanted visible light above the 70nm range.
Lum. =
Lumen - The international (SI)
unit of luminous flux or quantity of light. For example, a dinner candle provides about 12 lumens. A 60-watt Soft White
incandescent lamp provides 840 lumens. (Lumens = Mean
Spherical Candlepower x 12.57)
Luminance L = A
unit of measurement: candelas per square metre (cd/m²) The
luminance L of a light source or an illuminated area is a measure of how great an impression of brightness is created in the brain. - Osram Photo-Optic Lighting Products, 1999
Luminous efficacy ɳ =
Unit of measurement: lumens per
watt (lm/W).
Luminous efficacy indicates the efficiency with which the electrical
power consumed is converted into light. - Osram Photo-Optic Lighting Products, 1999
Luminous Flux Ф = a
unit of measurement:
Lumen (lm). All the radiated
power emitted by a light source and perceived by the eye is called luminous flux. - Osram Photo-Optic Lighting Products, 1999
Luminous
Intensity I =
Unit of measurement:
candela (cd). Generally speaking, a light source emits its luminous flux in different directions and a different intensities. The visible radiant
intensity in a particular direction is called luminous
intensity. - Osram Photo-Optic Lighting Products, 1999
Lumen Maintenance = A measure of how a lamp maintains its light output over time. It may be expressed as a graph of light output verses time or numerically.
All
metal halide lamps experience a reduction in light output and a very slight increase in
power consumption through life. Consequently there is an economic life when the
efficacy of the lamp falls to a
level at which is better to replace the lamp and
restore the illumination. Where a number of lamps are used within the same area it may be well worth considering a group lamp replacement programme to ensure uniform output from all the lamps.
Luminarie Efficiency = The ratio of total lumens emitted by a luminary to those emitted by the lamp or lamps used.
Luminarie efficiency (also known as light output ratio) is an important criterion in gauging the energy efficiency of a luminarie. This is the ratio between the luminous flux emitted by the luminarie and the luminous flux of the lamp (or lamps) installed in the luminarie. For detailed information on indoor lighting with artificial light, see DIN 5035. - Osram Photo-Optic Lighting Products, 1999
Luminance = Formerly, a measure of photometric brightness.
Luminance has a rather complicated mathematical definition involving the
intensity and direction of light. It should be expressed in candelas per square inch or candelas per square
meter although an older
unit, the “footlambert”, is still sometimes used.
Luminance is a measurable quantity whereas brightness is subjective sensation.
Luminous Efficacy = The light output of a high source divided by the total
power input to that source. It is expressed in lumens per
watt.
Lux (lx) = The SI (International)
unit of illuminance. One
lux is equal to 1
lumen per square
meter. See also footcandle.
MSCP = Mean
Spherical Candlepower, this value is the initial mean
spherical candlepower at design
voltage, subject to manufacturer tolerances, generally the accepted method of
rating the total light output of miniature lamps. See Candle
Power above.
Mean Lumens = The average light output of a lamp over its rated life. For
fluorescent and
metal halide lamps, mean
lumen ratings are measured at 40% of rated lamp life. For mercury, high pressure sodium and
incandescent lamps, mean
lumen ratings are measured at 50% of rated lamp life.
Neodymium Coating, a
Dichroic Coating on the lamp which reduces the yellow content of light, enhancing whites, reds, blues & Greens. These lamps are useful for merchandise displays, or on dimmed circuits to correct for amber
shift.
Nitrogen = Common inert gas filling other than
halogen for inside
incandescent lamps, This is usually a mixture of nitrogen and argon used in lamps 40watts and over to retard evaporation of the
filament. Smaller bulbs usually do not require gas and therefore are vacuum bulbs Krypton is limited in output and Nitrogen/Argon gasses
Tungsten =
Tungsten filaments change electrical energy to radiant energy. The light generated results from the
filament being resistance heated to a temperature high enough to produce visible light. Filaments can not be operated in air see seal and vacuum.
Tungsten is used for the filaments because of its low rate of evaporation at temperatures of
incandescence and its high melting
point 3,655°K. There are grades of
tungsten purity and different grain structures. Only the highest grade of an elongated grain structure guarantees maximum life and reliability during
shock and vibration. Heat treatment of the
tungsten filaments is one of the most critical factors in lamp manufacturing.. Proper heat treatment prevents
filament sag, abnormal coil shorting or premature breakage.
Tungsten Halogen Lamps =
Halogen Lamps are
tungsten fliament
incandescent lamps filled with an inert gas (usually krypton or xenon to insulate the
filament and decrease heat losses) to which a
trace of
halogen vapor (bromine) has been added.
Tungsten vaporized from the
filament wire is intercepted by the
halogen gas before it reaches the wall of the
bulb, and is returned to the
filament. Therefore, the glass
bulb stays clean and the light output remains constant over the entire life of the lamp. (p33, Sylvania Lamp &
Ballast Product Catalog 2002)
Halogen lamps are high pressure
incandescent lamps containing
halogen gasses such as iodine or bromine which allow the filaments to be operated at higher temperatures and higher efficacies. A high-temperature chemical reaction involving
tungsten and the
halogen gas recycles evaporated particles of
tungsten back onto the
filament surface. Also called a Quartz lamp, though this is a term for the higher melting temperature glass enclosure used on
halogen lamp
v = Volts - A measurement of the electromotive force in an electrical
circuit or device expressed in volts.
Voltage can be thought of as being analogous to the pressure in a waterline. The
effect of
voltage on a lamp will cause a significant change in lamp performance. For any particular lamp, light output varies by a factor of 3.6 times and life varies inversely by a factor of 12 times any percentage variation in supply. For every 1% change in supply
voltage light output will rise by 3.6% and lamp life will be reduced by 12%. This applies to both DC and
AC current. Most standard
line voltage lamps are offered at 130v. Since most
line voltage power is applied at 120volts, the result is a slight under voltaging of the
filament. The
effect of this is substantially enhanced lifehours, protection from
voltage spikes and energy cost savings.
Voltage and Light Output: The
effect of
voltage on the light output of a lamp is ±1%
voltage over the rated amount stamped on the lamp, gives 3.1/2% more light or Lumens output but decreases the life by 73% and vise a versa.
Do not operate quartz Projection lamps at over 110% of their design
voltage as rupture might occur. GE Projection, Ibid p.13
Xenon (High output
halogen lamps using Xenon filler instead of krypton producing a luminous flux up to 10% higher; with otherwise identical lamp data
Quartz Lamp “QI”, or Quartz-Iodine Lamp. Introduced in 1959, this small, compact, long-life lamp consisted of a
tungsten filament enclosed in a transparent quartz
envelope partially filled with vaporized iodine. When an ordinary lamp burns, tiny particles of
tungsten are released from the
filament and are deposited on the glass
envelope as a black film, gradually reducing the
intensity of the light. During the burning process of the quartz-iodine lamp, released particles of
tungsten reacted chemically with vaporized iodine and returned to the
filament. Not only was the life of the lamp improved by this, but the black deposits on the inside of the
envelope were eliminated. The ideal lamp had been created except for one small detail: as iodine sublimes, it turns a purple-violet color in both the warming (dim-up) and cooling cycles. Clearly, the untenable situation for theater lighting. Further experiments substituted a related
element,
halogen, for iodine and heat resistant quartz glass for the quartz
envelope, producing a lamp that retained the favorable characteristics of the quartz-iodine lamp and eliminated the purple discoloration. The new lamp was redesigned and introduced to the market as a
tungsten-halogen (TH) lamp. The term “Quartz” carried over.
Tungsten Halogen (TH, quartz iodine, QI). A lamp using a
halogen gas around a compact
filament. Used in instruments designed specifically for this type of lamp, the TH lamp can also be retrofitted for older instruments. It should be noted that the terms “QI”, “Quartz”, and “quartz iodine” are “misnomers” in common usage. (
Theatre Lighting from A to Z by Norman C Boulanger and
Warren C Lounsbury, University of Washington Press, Seattle 1992) The
Halogen lamp was invented by G.E. Lighting in 1957. (G.E Spectrum, Ibid p.2-1)
Tungsten-Halogen Lamp (TH, quartz, QI). The
tungsten-halogen lamp is made with a heat-resistant synthetic quartz
envelope, filled with
halogen gas. Under the intense heat of the burning process, bits of
tungsten released from the
filament react chemically with the
halogen to
return to the
filament. The process not only improves the life of the lamp but eliminates black deposits on the inside of the
envelope that with standard
tungsten lamps filled with inert gases. Another favorable feature of TH lamps is that they burn equally well in any position and therefore have made possible improvements in the design of instruments, including the
axial mount
ellipsoidal reflector spot light such as the
Altman 360 being made into the
360Q. Because TH lamps offer higher
intensity, longer life, and soot-free envelopes, they are obviously the favored lamps for stage-lighting instruments. Warning however, do not touch the synthetic quartz
envelope of the lamp with bare fingers; skin oil deposited on the
envelope will cause hot spots to develop when the light is turned on, shortening the life of the lamp. (
Theatre Lighting from A to Z) Normal
lamp globe temperature is 482°F minimum, hot spots on the
bulb wall itself can go as high as 1,230°F. in normal operation. Use the paper or plastic wrap which comes with the lamp to
shield it while handling. Clean dirty or touched lamps only with alcohol or grease free
solvent. Keep sealed
fixture temperatures below 350°C. Bulbs on the other
hand must maintain (482°F) 250°C for operation of the
halogen cycle.. To avoid
shock when on, do not operate them beyond 8-10% of their total rated
voltage (by the
safety specs), 3,400K Quartz lamps should not be operated above 105% of their
voltage or life will be seriously effected, under
voltage operation under 90% of their rated
voltage gives longer but un-predictable length extended life, however
transformer type dimmers adjusting the
voltage of a quartz lamp will preserve more lamp life than semi-conductor dimmers due to the type of dimming work actually done. (G.E, Ibid p58) Quartz lamps may begin to devitrify at temperatures above 1,832°F. The best operating range for a
halogen lamp is 482-1,472°F. Oxidation on the sealing foil carrying
current from the
base to the
filament however begins to oxidize at temperatures above 662°F. Lamp life may be shortened by premature seal failure if this temperature is exceeded. (G.E. 99, Ibid p.6-5) Contact pins are plated to ensure good electrical connection with the
lampholder. However, at temperatures above 662°F. the plating may loose adhesion, leading to deterioration in contact and possibly local hot spots, arcing and consequent irreparable damage to both lamp and holder. Note that if there is evidence that this has occurred, the
lampholder should be replaced before the next lamp is fitted, otherwise it is likely to fail prematurely for the same reason. Lamps normally fail by fusing of the
filament. This is often followed by arcing, leading to very high currents which can cause the
envelope and seals to fail and the lamp to shatter. A quick-acting, high breaking capacity
fuse should therefore be connected to the supply
line in all applications suitable types are given is
IEC 127, 241, and 269. Because of the heat involved with
line voltage halogen lamps, do not use them in fixtures not rated for their use, or at least 660V constant operation high temperature plastic or
porcelain, or in fixtures with cooling fins on their
base, reflectors or anything else needed for extra cooling of the equipment. (G.E Spectrum, Ibid p.2-17) Normal operating temperatures of a
halogen lamp are above the flash
point and kindling temperatures of many materials and lamp bases, care should be taken when using them. Temperatures above 350°C should be avoided when using a
halogen lamp as they might deteriorate the lead wires and basing cement can loosen causing lamp failure. (GE Miniature & Sealed Beam Lamp Catalog, G.E. Lighting # 208-21121 (9/92) p. 23)
Halogen lamps operate at near 100% efficiency throughout their life, and generates 1/3 more light per
watt than
conventional incandescent lamps (Philips, Ibid p.111) 68% more energy cost savings over
Incandescent and 50% more life. (G.E. 99, Ibid p. I-5) Substantial heat is generated in all
halogen lamps (90% of their light is
infrared and a small amount is UV which can be protected against by almost any
screen or
lens) (G.E Spectrum, Ibid p.17), so equipment design should make allowance for the dissipation of excessive heat. Certain lamps and extremely confined fixtures may require additional ventilation or heat sinking to ensure proper operation of the
halogen cycle and to prevent damage to the
fixture. It is a good practice to test the lamp in the operating environment early in the design cycle to ensure adequate performance. Precautions must be taken in the selection of materials for lamp holders, reflectors, and lamp housings because the 1230°F.
bulb wall temperature is greater than the kindling temperature of many materials. Lamp
base temperatures should not exceed 662°F. because above that
point, lead wires may deteriorate and the basing cement loosen, causing premature lamp failure (G.E.99, Ibid p.2-15)
Avoid lamp use on dimmers which can deliver
voltage over their rated
voltage, do not allow one lamp to directly touch another lamp, and do not allow particles to fall on the lamp they can cause hot spots on the lamp. (Ushio, Ibid p.28) Extended exposure to un-jacketed lamps rated at 3,200K and above, or to any un-jacketed quartz lamps operated above rated
voltage, may lead to ultraviolet irritation of skin and eyes. Passing the light through ordinary glass or plastic provides adequate protection. Such protection is automatically provided by the glass of outer bulbs of quartz
Par and R-lamps. (G.E, Ibid p.54) Noise - all Quartz
stage and studio type lamps except
Par types have special “low noize” construction to minimize generation of audible noise when operatid on A.C. circuits. In addition all Quartz
RSC lamps have such construction. (G.E, Ibid p.57) The most powerful Quartz lamp is 20,000 KW.
Halogen Lamps: to clean touched lamps use alcohol and a clean cloth if touched or dirty, better yet do not touch a
halogen lamp as the oils from ones fingers will stay on the glass and cause heat to not dissipate as well. Sometimes these areas can burst or swell up in time. They can also reflect heat and cause the
filament to become misshaped even to the
point of it touching the opposite side of the lamp and melting its way
thru the glass. In this case, even if the
filament does not break, the
focus point of light will be out of focus. Also always allow a lamp or
fuse to cool before touching it even with gloved hands, as the glass might explode.
ANSI lamps and generalized data do not necessarily mean every lamp brand producing the same lamp will have the exact performance data. Materials which make up the lamp
play a large part in the
lumen output and life of a lamp. Factors affecting this are: the grade of quartz (it purity its preparation and
transparency) (Ushio, All Lamps Are Not Created Equal, Ushio Pamphlet), the cement and
ceramic materials strength and durability, the gas selection - mixture and fill pressure. (The choice of gas is critical as well as its pressures and organic carriers: see chart below.) The
tungsten filament ([K2O-SiO2-Al2O3 family] having a low rate of evaporation at high temperatures, and is easily formed into complex shapes necessary for the
filament. Different treatments during the production of the
tungsten wire affect the
filament’s properties. For example, the
introduction of re-crystallized particles along the length of the
wire makes it possible to produce filaments which remain
distortion free. Such non-sagging filaments are critical in many applications.) ( Ushio All Lamps, Ibid) The
filament must be formed and coiled to the right specifications, and assembly must be done in a clean environment. (the sealing must withstand an increase in temperature from ambient to 250°C. and still keep its seal. Forming the seal is critical to making a good lamp, molybenum foil is used since it expands at almost the same rate as quartz when it is heated. Since the rates do not match perfectly, the stress on the seal area must still be minimized by chemically milling the edges of the foil of the thinnest feasible cross-section, it is possible to improve the seal performance further. Such proprietary techniques differ from one lamp maker to another and serve as examples of the differences in manufacturing technique which impact on lamp performance and consistency.) (Ushio All Lamps, Ibid) Any scaling down of these features will probably be reflected in the price and quality of a lamp. (Ushio Lamp Promotion, Special Promotional Pricing for Distributors, Ushio#P004/0500 c5/1/2000 p.5) There are more than twenty companies which manufacture lamps today. There are also a number of companies selling lamps that are private labeled for them. The manufacturers are generally divided into two groups: companies products primarily for general lighting and those producing lamps for special applications. The requirements for success are different. Products for general lighting are typically manufactured in high volumes. Being able to design,
build and operate high speed production lines is critical. Specialty product manufacturers usually concentrate on producing small quantities often with more specific design goals and tighter tolerances. Their challenge is to maintain consistency since unexpected lamp failures can result in down time costing many thousands of dollars per hour. (Ushio All Lamps, Ibid)
Most typically today, bromine or iodine are used as the active
halogen components. Nitrogen, argon and sometimes krypton gases from the atmosphere. The choice considers thermal losses, arcing
voltage, molecular mass and cost among other factors. ( Ushio All lamps, Ibid)
Heat Impact Resistance - The quartz glass
envelope signifies that
halogen lamps are much more resistant to heat impact than ordinary
incandescent lamps. There is almost no danger that a lit
halogen lamp will break even if it should come into contact with cold water.
Halogen Cycle - When the
filament is heated to a high degree, the
tungsten evaporates and reacts chemically with tie iodine gas (
halogen gas) inside the
bulb to produce
tungsten iodide near the
bulb wall. The
tungsten iodide particles are moved by convection within the
bulb and, when they approach the highly heated
filament, they are decomposed once again into iodine and
tungsten. The
tungsten returns to the
filament once more and the same cycle is then repeated. The process, called “
Halogen Cycle,” effectively prevents blackening of the
bulb wall and thinning of the
filament’s
tungsten, thus resulting in longer lamp life. (Ushio
Halogen Lamps, Ushio Pamphlet #94-3-1000 YO(24) Japan pp.1-2)
Interference Filters: These filters are sometimes called “
Dichroic”and provide selective transmission of radiant energy. They are generally used to transmit light and reflect the invisible radiation. (1) Infra-red in the beam is minimized (up to 85% reduction) with no significant loss of light. Re-directed radiant energy is deflected to a heat Absorbing collecting surface which must be cooled by more
conventional air or water techniques.
Note (1): Interference filters are also available as “cold mirrors” to reflect light and transmit
infrared. These are useful for reflecting contours. “
Dichroic Beam Splitters” act down range of the lamp, and act as a
lens transmitting light while reflecting radiant heat.
Transmission: Light Approx 92%, IR Approx 15%
Heat Absorbing Glass: These materials tend to absorb some energy in the visible spectrum as well as infra-red. However, some types are relatively effective—absorbing as much as 80% of the infra-red while transmitting approximately 75% of the light. Because heat is principally absorbed (rather than reflected) a temperature rise occurs n the glass it-self. This surface tends to become a radiant heating panel unless effective air circulation is provided to minimize the build-up of heat.
Transmission: Light Approx 75%, IR Approx 20%
Water Filters: Many liquids will absorb large portions of the infra-red energy while transmitting most of the visible wavelengths. A one-inch
thickness of water, for example, will absorb approximately two-thirds of the invisible energy. While such a circulating water
system is not a normal procedure, it may be useful in limited situations, particularly in conjunction with other water-cooled panels.
Transmission: Light Approx: 85% I.R. Approx 30%
Incandescent Lamps: The efficiency and operation of a
filament lamp is relatively unaffected by temperature. However, the
effect of heat on lamp and
fixture materials may be a critical design consideration. (Also see “Lamp Heat Emission”)
Ambient Temperature: The
filament itself operates at a very high temperature (E.G. 4,000-5,000°F.), so any normal change in air surrounding a
bulb is relatively insignificant and will not affect
filament temperature. Since
filament temperature is neither increased nor decreased, there is no adverse
effect on lamp life or light output.
Bulb Temperature: If a region on the
bulb is heated to the softening
point of glass, a blister or
bubble will develop due to the pressure of the gas inside. Most general-purpose lamps produce maximum
bulb temperatures below 500°F (and often below 300°.) With higher wattage lamps and with compact special-purpose sources, however, the glass temperatures may be a design consideration.
Maximum Safe Operating Temperature for
Bulb Glass: (Approximate)
Soft, Lime Glass 700°F.
Hard, Heat-Resistant Glass 855°F.
Molded, Heat-Resistant Glass 975°F.
Quartz Tubing 3,000°F.
Bulb Position: Because Convection Heat Rises, location of the “Hot Spot” will vary with the
bulb position. Some lamp types are limited to certain burning positions to insure that glass temperature limits are not exceeded.
Base Up lamps have convection of heat flowing upwards from the
filament along the lead-in and support wires (at the center) to the
base of the lamp. From there, it is turned around (in a high pressure exchange due to the amount of heat convection verses the size of the stem,) and flows along the outside of the
bulb until it hits the top of the
envelope which is in a down position, than back into the
filament to be re-circulated. How the
filament is supported, especially on C type single
filament lamps is also a major factor in burning position, horizontal/
base up or down. are all factored into the design and
layout of the hangers/supports, and how tight they keep the
filament or how much sag/stretch and eventual breakage is countered by the supports fixed in a ceratin position.
Internal Convection:
Base Down lamps flow in the opposite direction (
filament to top of
envelope, around the
bulb to the stem/
base, than back up the center to the
filament.) except not all of the circulating air reaches the
base of the lamp. The lamp
base on these lamps is slightly cooler than on
base up lamps because less convection heat is directed or forced into the smaller turbulent area of the lamp
base. The heated air/gas flowing in this area (having already circulated over ½ way around the
bulb does not have the pressure to force its way into the turbulence of the lamp
base/stem, thus leaving the
base cooler because it does not contact as much heat. The overall
globe temperature and amplitude of heat circulating is more however through the
filament because of the shorter path of circulation of the heat. These differences in circulation of heat within the lamp are important factors when things like
porcelain verses plastic lamp bases are in question (See “Chimney
Effect” Below,) or in the composition of the materials making the lamp and its efficiency verses wattage are involved.
Reflector Focus of Energy: When circular or
spherical reflectors are used to re-focus light, the physical position of vulnerable lamp parts becomes a design consideration — to prevent a focus of radiant energy on the
bulb filament. Such concentrations of heat, whether caused by faulty design or maladjustment of the
unit, can cause glass failure.
Exposure to Water: Gas-Filled lamps must be protected from localized cooling (thermal
shock) due to rain, snow, or even large bugs. This causes
bulb breakage. Glass
cover plate (or screens) are used for protection (given proper ventilation or high temperature lamps to counteract the increased heat)
or hard glass bulbs may be used.
Contact with Metal: Thermal cracks may result from metal
fixture parts touching the
bulb. Localized cooling causes internal stress and can cause glass failure. Note