Preheating Conventionals?
- Thread startergafftaper
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dj_illusions
Active Member
I have a funny feeling in our venue which is fully air condition with industrial kitchen, multiple small event rooms, offices, computers etc. preheating lamps for 5 minutes before a show is barely going to register on the power meter compared to the power that is been drained by all the other electrical equipment currently running.
If we are concerned about electricity, switch off the air conditioner for 5 minutes while preheating, im guessing this is going to save more energy than not preheating lamps for a whole year....
The issue was extended lamp life, i was trying to keep out of this discussion, i dont preheat lamps every time before a performance, but personally believe that preheating the lamps for a short period of time does improve the lamp life and also help condition the fixture, if you are stretching your filament before the show it is not put under as much strain when bumped to full as it would be without a preheat, i still see benefits in doing this and as many others have said even if it is not necessary it is a good practice as it forces you to do your lamp and gel check at the same time.
If we are concerned about electricity, switch off the air conditioner for 5 minutes while preheating, im guessing this is going to save more energy than not preheating lamps for a whole year....
The issue was extended lamp life, i was trying to keep out of this discussion, i dont preheat lamps every time before a performance, but personally believe that preheating the lamps for a short period of time does improve the lamp life and also help condition the fixture, if you are stretching your filament before the show it is not put under as much strain when bumped to full as it would be without a preheat, i still see benefits in doing this and as many others have said even if it is not necessary it is a good practice as it forces you to do your lamp and gel check at the same time.
Finally have time to put in my two sense. Anyway, great debate going on here. I am, however, with allthingstheatre. ETC makes HPL lamps for 115v, 120v, 230v, and 240v. The reason being that is the resitance in each of these lamps is different for each voltage lamp to get the 375w, 575w, or 750w you are looking for.
750w/115v=6.52a; 115v/6.52a=17.64 ohms. 750w/120v=6.25a; 120/6.25a=19.2 ohms.
Now let's try a lower voltage on a 120v lamp: 115v/19.2=5.99a; 115*5.99a=688.85w.
And a higher voltage on a 115v lamp: 120v/17.64=6.80a; 120v*6.80a=816w.
They make these different lamps to make sure you get the wattage you want at max voltage. Using to much voltage on a 115v lamps shortens the life. Using to little voltage can also have the same effect, because that lamp wants to be at 750w, 575w, or 375w. Thats what is was designed to operate at. Now went ETC says it takes a regular 750w or 575w lamp 300 hours till failure, thats mean time till failure. That means they took hundreds of lamps, ran them all over the place voltage wise, and ran them till they blew. The bulk of those lamps I am sure were at the recommended voltage, meaning they are most statistically significant. Its says +/- 10% at the bottom of ETC's page for lamp life, which is just statistical as well. I had an HPL blow within a couple hours of use before, and I am sure I have had them last longer then 1500 or 300 hours. Preheating, as stated, does nothing more then take lamp life off the lamp and use power. Why do I say this, because there are two laws that govern the universe, minimal energy, maximum disorder. Running those lamps slowly to whatever percentage puts them in a constant change of state, which things in the universe don't like, hence minimal energy. That lamp wants to run at whatever it was designed for, and thats the optimum lamp life for it.
750w/115v=6.52a; 115v/6.52a=17.64 ohms. 750w/120v=6.25a; 120/6.25a=19.2 ohms.
Now let's try a lower voltage on a 120v lamp: 115v/19.2=5.99a; 115*5.99a=688.85w.
And a higher voltage on a 115v lamp: 120v/17.64=6.80a; 120v*6.80a=816w.
They make these different lamps to make sure you get the wattage you want at max voltage. Using to much voltage on a 115v lamps shortens the life. Using to little voltage can also have the same effect, because that lamp wants to be at 750w, 575w, or 375w. Thats what is was designed to operate at. Now went ETC says it takes a regular 750w or 575w lamp 300 hours till failure, thats mean time till failure. That means they took hundreds of lamps, ran them all over the place voltage wise, and ran them till they blew. The bulk of those lamps I am sure were at the recommended voltage, meaning they are most statistically significant. Its says +/- 10% at the bottom of ETC's page for lamp life, which is just statistical as well. I had an HPL blow within a couple hours of use before, and I am sure I have had them last longer then 1500 or 300 hours. Preheating, as stated, does nothing more then take lamp life off the lamp and use power. Why do I say this, because there are two laws that govern the universe, minimal energy, maximum disorder. Running those lamps slowly to whatever percentage puts them in a constant change of state, which things in the universe don't like, hence minimal energy. That lamp wants to run at whatever it was designed for, and thats the optimum lamp life for it.
Actually I believe average lamp life is calculated by running the test group of lamps at full until they burn out. This is because the lamp life rating is based on ideal operating conditions which for an HPL575/120v would be at 120v providing the most efficient halogen cycle. They take note of when each lamp burns out and then calculate the average life. The +/-10% says that in general lamps last within 10% of the rated life. Lamps do last longer if run under their rated voltage, we talked about that in another thread, and I believe Ship gave us a formula to approximate the change in lamp life when voltage is changed.
If you have had lamps last on the order of 1500 hours then you probably had an HPL "X" lamp which is rated to 1500 hours. While it may be possible for a 300 hour lamp to burn for 1500 ours, it is highly unlikely. There are many things that can shorten lamp life, so having a 300 or 1500 hour lamp only last half that is possible.
So, that still brings us back to the preheating question. It isn't a question if if preheating will make you lamp last longer than the rated lamp life, it is a question of if preheating will make the lamp last longer than not preheating the lamp.
Probably the ideal test would be to take two identical fixtures and lamps from the same lot, Preheat one at some low lever for some time and then turn both fixtures on to full in a 0 count. Let the fixtures burn for about 4 hours a day and repeat each day until one dies. I picked a 4 hour burn time because most theatres probably don't run their lamps for more than 4 hours a day. Running the lamps at full gives us optimum operating conditions, so we should get close to the rated lamp life.
That is exactly what I proposed.
All we need is a dealer or manufacturer to supply the equipment.
David Ashton
Well-Known Member
A very important fact which I have not seen mentioned is that
"the laws governing the relationship between voltage and lamp life in quartz halogen lamps only apply
at and above 80% of the rated voltage which is the point at which the halogen cycle kicks in".
So all the pre-heating time is stripping tungsten off your filaments which is not replaced until you bring it up to over 80%
"the laws governing the relationship between voltage and lamp life in quartz halogen lamps only apply
at and above 80% of the rated voltage which is the point at which the halogen cycle kicks in".
So all the pre-heating time is stripping tungsten off your filaments which is not replaced until you bring it up to over 80%
JD
Well-Known Member
Found a neat PDF about light bulbs while researching the current thread. http://physicsed.buffalostate.edu/pubs/TPT/TPTDec99Filament.pdf
Here is a little quote from the article that I think we all overlook a bit:
--------(quote)----
"Halogen lamp filaments not only can be run hotter and more efficiently, but must be run at higher temperatures to initiate and sustain the halogen cycle. Therefore, for halogen bulbs, a very small tubular envelope made of fused silica (a noncrystalline quartz) is operated at temperatures up to 1200 8C (depending on bulb type and wattage), together with a high-pressure fill gas (about five atmospheres). To ensure full lamp life, halogen filaments should be run at least 20 minutes to initiate the halogen gas cycle and fill-gas convection."
---------(end quote)----
The "Overlooked" part is that little blurb that the bulb must be on for 20 minutes for the cycle to work!
One thing more about preheats. Tungsten does not really start evaporating in mass until the filament is white hot. A 120 volt lamp run at 30 volts will probably outlive all of us! A friend of mine keeps mold out of his classic car that is in storage by keeping light bulbs lit in it. It is a string of three 100w lamps in series, which to date has been lit for 20 years and counting! (all original bulbs.)
Here is a little quote from the article that I think we all overlook a bit:
--------(quote)----
"Halogen lamp filaments not only can be run hotter and more efficiently, but must be run at higher temperatures to initiate and sustain the halogen cycle. Therefore, for halogen bulbs, a very small tubular envelope made of fused silica (a noncrystalline quartz) is operated at temperatures up to 1200 8C (depending on bulb type and wattage), together with a high-pressure fill gas (about five atmospheres). To ensure full lamp life, halogen filaments should be run at least 20 minutes to initiate the halogen gas cycle and fill-gas convection."
---------(end quote)----
The "Overlooked" part is that little blurb that the bulb must be on for 20 minutes for the cycle to work!
One thing more about preheats. Tungsten does not really start evaporating in mass until the filament is white hot. A 120 volt lamp run at 30 volts will probably outlive all of us! A friend of mine keeps mold out of his classic car that is in storage by keeping light bulbs lit in it. It is a string of three 100w lamps in series, which to date has been lit for 20 years and counting! (all original bulbs.)
I'd like to jump in.
This has been an interesting debate. I have three points.
I can see where preheating would be ineffective for HPL's and the like, but is there any merit to pre-heating, 5, 10 or 20K's?
It seems like that running your lamps at 80% or more on a regular basis would be better for life as it would help replace lost tungsten through the tungsten cycle. However, one must remember that tungsten is NOT replaced evenly.
Preheating has been around for a long time. Might preheating have been effetive on the older tungsten, non-halogen lamps. I really don't see how it would have been, but just have the question in my mind.
This has been an interesting debate. I have three points.
I can see where preheating would be ineffective for HPL's and the like, but is there any merit to pre-heating, 5, 10 or 20K's?
It seems like that running your lamps at 80% or more on a regular basis would be better for life as it would help replace lost tungsten through the tungsten cycle. However, one must remember that tungsten is NOT replaced evenly.
Preheating has been around for a long time. Might preheating have been effetive on the older tungsten, non-halogen lamps. I really don't see how it would have been, but just have the question in my mind.
David Ashton
Well-Known Member
May years ago I worked in the Isle of Mann on a big resistance board and in the winter the grease on the bearings would congeal so I would run the lights at about 3 for 15 minutes to warm up the bearings and the operator.Unlike the filament of a lamp a resistance board has a large thermal mass and so stays warm.The basic question is" how long does it take for my pre-heated thing to return to its original temperature", if the answer is under a minute then clearly pre-heating it 30 minutes earlier is a waste of time, energy and lamp-life. QED
Urr, please state where you got this info from. I don't think your reference is corrct in being used for line voltage lamps where from all info I am aware of or have been told, the halogen cycle takes place within the lamp at all stages of dimming where the filament is hot enough to project light. Also, the effects of lamp life on lamps under dimming has been well stated by me over the years so I won't repeat it but the effects of dimming on a 300 hour lamp is extending it exponentially beyond that at full voltage rating. Even a 5% change in the voltage applied to the lamp will etend it's lamp life by 60% for the time that lamp was on at 5%.
(Side note, not seeing much about trim settings on one's dimmers / pre-heat voltages applied to the lamps already in this discussion.)
Here is a similar tidbit about low voltage lamps which might be the source of confusion:
Low Voltage Dimming: Low Voltage halogen lamps should not be dimmed by more than 10% of their rated voltage since this will result in a reduction in life. Standard tungsten filament lamps (with no halogen filling), can be dimmed to zero volts, resulting in virtually endless life. However if low voltage tungsten halogen lamps are dimmed by more than 10%, the lamp will be operating at too low a temperature and the free halogens in the gas fill, will attack the cooler parts of the tungsten filament i.e. where enters the quartz or glass envelope. The wire at that point will then be eroded and eventually will fail. So if dimmed by 10% or more low voltage tungsten halogen lamps will not have an extended life but are unlikely even to reach their rated life. - Philips Website, Optical p1.
Also:
Osram offers landing and take-off lamps in a wide range of wattages. These lamps are designed to operate in series and will last on average for 1,000hours. Thanks to modern halogen technology, the lamps can be operated well below their current rating with no loss of service life.
And:
Operating Temperature = The following maximum and minimum temperatures are suggested for optimum life in tungsten halogen studio lamps. Operation outside these figures will not necessarily cause immediate failure but will affect life adversely to an increasing extent. Seal temperature - 450̊C max. Above this figure the sealing foil oxidizes at a rate increasing with temperature and is frequently the cause of short life due to seal temperature. (The point to which gas is injected into the globe.) Bulb/Globe - 250̊C to 800̊C - outside this range the halogen cycle becomes less efficient and blackening may occur. Temperatures above 1,200̊C will cause the bulb to soften. Pins - 350̊C maximum. Above this figure the plating on the pins may lose adhesion and the contact will deteriorate. Such deterioration may form local hot spots which rapidly worsen and may result in arcing and irreparable damage to both lamp and holder. Should signs of this be evident on removal of a failed lamp, it is important that a good contact is restored by replacing the lampholder before the next lamp is fitted. Otherwise the new lamp will rapidly fail in a similar manner. (Unknown source)
Series Operation = Life of a lamp can be severely reduced by using a series application because of the different resistances of the lamps used in the circuit. The applied voltage is not distributed evenly over all of the lamps in the series, so each lamp is operating at a slightly different voltage. This means embrittlement and the evaporation rate will not be equal, so some lamps could fail prematurely. It is recommended that lamps be selected for amperage and operated at a derated voltage for maximum reliability in series operations. (Unknown source)
Than:
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 3,655̊K. 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)
David Ashton
Well-Known Member
I pulled that off the GE site, however the halogen cycle is a function of temperature and the voltage of the lamp is not an issue.I am puzzled as to why you might think that the mechanics of the halogen cycle would change with voltage.
If you are referring to Ship's mention of low voltage lamps, then I don't think what is meant is that the halogen cycle is affected by voltage. The halogen cycle is affected by heat, and low voltage lamps produce less heat than line voltage lamps, so if you dim them down they produce even less.
David Ashton
Well-Known Member
The heat in a lamp has virtually no relation to voltage, it is a straight function of wattage, except for a tiny gain in the percentage of heat converted to light, and where does low voltage begin? a high voltage and low voltage lamp contain the same materials doing the identical physical and chemical reactions at the same temperature, a longer filament is the only essential difference.
JD
Well-Known Member
Well, almost straight. It's actually a ratio between the wattage and the envelope size. That's why quartz bulbs are small, to get the surface temperature high.
One thing I have noticed is that enclosed quartz lamps (think par) are less likely to "cloud" over than open air quartz lamps. I suspect air convection cooling the envelope faster is the cause.
One thing I have noticed is that enclosed quartz lamps (think par) are less likely to "cloud" over than open air quartz lamps. I suspect air convection cooling the envelope faster is the cause.
Wattage is a function of voltage. If resistance is constant (which in theory it is for any given lamp) and the voltage changes, then the number of amps has to change. It's Ohm's Law, V/I=R (I=Amperes). Then if you take the volts and amps and plug into Watt's law W=VA then you have wattage changing based on voltage. Therefore if you say that temperature is a function of wattage it is also a function of voltage.
Higher voltage lamps have to have a higher resistance in order to output the same wattage as lower voltage lamps. Here is an example:
120W 120v lamp draws 1A - 1Ω resistance
120W 12v lamp draws 10A - 0.1Ω resistance
In theory, more resistance equals more heat. So in theory heat has more to do with the resistance of a lamp than the wattage.120W 12v lamp draws 10A - 0.1Ω resistance
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Radman
Well-Known Member
Unless your power is underground all the way to the power plant, I wouldn't feel so safe. I worked in a theatre where the power was underground where it came to the building and probably stayed underground for a few miles, but eventually it comes up and hooks on to bigger branches of the distribution system. A tree fell on a line out in the country miles away and screwed up the dimmers and console for the whole first act of a show.
David Ashton
Well-Known Member
I'm not an electricity wizard like some of you guys but I do vaguely remember being taught that resistance is not constant. As heat increases resistance increases. I found this on the internet:
"Resistance also depends on temperature, usually increasing as the temperature increases. For reasonably small changes in temperature, the change in resistivity, and therefore the change in resistance, is proportional to the temperature change. At low temperatures some materials, known as superconductors, have no resistance at all. Resistance in wires produces a loss of energy (usually in the form of heat), so materials with no resistance produce no energy loss when currents pass through them. "
The website also has a formula for calculating the temperature effect on resistance... which doesn't copy due to the font I guess.
I also found this site with a nifty little demo video that shows how as a wire is heated resistance drops and the battery powered lamp gets dimmer. Granted they are heating the line carrying power to the lamp and not the lamp itself.
While this undermine's Alex's previous point, I'm pretty certain that the "all 100 watt lamps are the same temperature" theory is also wrong. When I teach my beginning students about Lumens and foot candles I start with house hold lamps. I show them that when looking at a household "light bulb", they should think about wattage only as a measure of how much energy is consumed, not as a measure of how bright it will be in their kitchen. I show them that if you go to a big hardware store that carries four brands of 100 Watt bulbs you will find they all have different lumen ratings. In this case I would also argue that wattage has very little to do with how hot a lamp is for the same reason. By using different conductive materials, gases, and envelops you could in theory construct a lamp that consumes a 100 watts of power but is barely warm to the touch (it might be 10' across and only last a few minutes but it's possible) or you could make one that can only produce 50 Foot Candles of light (charred bamboo filaments anyone?). The efficiency of the system that is inside the lamp is far more important than the wattage rating. I'm quite confident that four different household 100 watt bulbs would all have different operating temperatures.
"Resistance also depends on temperature, usually increasing as the temperature increases. For reasonably small changes in temperature, the change in resistivity, and therefore the change in resistance, is proportional to the temperature change. At low temperatures some materials, known as superconductors, have no resistance at all. Resistance in wires produces a loss of energy (usually in the form of heat), so materials with no resistance produce no energy loss when currents pass through them. "
The website also has a formula for calculating the temperature effect on resistance... which doesn't copy due to the font I guess.
I also found this site with a nifty little demo video that shows how as a wire is heated resistance drops and the battery powered lamp gets dimmer. Granted they are heating the line carrying power to the lamp and not the lamp itself.
While this undermine's Alex's previous point, I'm pretty certain that the "all 100 watt lamps are the same temperature" theory is also wrong. When I teach my beginning students about Lumens and foot candles I start with house hold lamps. I show them that when looking at a household "light bulb", they should think about wattage only as a measure of how much energy is consumed, not as a measure of how bright it will be in their kitchen. I show them that if you go to a big hardware store that carries four brands of 100 Watt bulbs you will find they all have different lumen ratings. In this case I would also argue that wattage has very little to do with how hot a lamp is for the same reason. By using different conductive materials, gases, and envelops you could in theory construct a lamp that consumes a 100 watts of power but is barely warm to the touch (it might be 10' across and only last a few minutes but it's possible) or you could make one that can only produce 50 Foot Candles of light (charred bamboo filaments anyone?). The efficiency of the system that is inside the lamp is far more important than the wattage rating. I'm quite confident that four different household 100 watt bulbs would all have different operating temperatures.
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