What's the lamp and
ballast you intend to use? Especially if electroinc or magnetic and the
Ballast's
ANSI code.
Lamp's wattage and description?
I’m not an expert on the subject of arc source fixtures nor dimming them but if of help I have looked into it some and have some starting points to consider. Not enough time in the day for me to start tinkering with the subject, nor is arc source gear my specilty, but some things that can be interesting to look into on a subject that comes up at times at work when some designer has a wacky idea.
I do know a very specific amount of caution I would follow in experimentation with this. Primary with this is that should the lamp or any part of the
fixture while dimming receive a jump in
current something very much could explode in a very dangerous way. The higher the pressure the lamp capsule operates under (AU), the easier it should be to control dimming it without losing the arc, on the other
hand this also means the more explosive the lamp will be should something go wrong. Heard my first arc source lamp go bye bye today. Also saw some of the glass that came out of an enclosed housing. Even if cold and more normal in size, I once broke a 400w
mercury vapor lamp by accident that was on my
desk. Glass did go everywhere including just missing my eyes.
For fixtures in how they dim safely or operate, one might look into the
Martin Mac 550. I believe it’s dimmable. What types of control chokes
etc. are in us could be of interest. There is also a lot of dimmable florescents on the market.
Most HR -
Hot Restrike lamps
stage and studio are fully dimmable while maintaining a stable constant
color temperature. This as opposed to the
color temperature of a
incandescent lamp which drops while dimmed with the luminous output. This
color temperature not dropping in an arc source lamp when dimmed should be the same with any arc source lamp.
On the other
hand, the above lamps are designed to be dimmed. Other lamps while they might be observed to dim well enough could receive some damage from dimming which would
effect it’s life, ability to maintain an arc and receive
pinch seal problems. Some more modern lamps such as the CMH
line from GE advertise a smaller lamp size which helps in
hot restrike, faster warm
ups and in theory given these common traits it should be fairly dimmable. It’s
ceramic capsule/arc tube on the newer style lamps also help to prevent against sodium seeping
thru the quartz glass which might become a problem while operating at less than peak
voltage or operating conditions. Also the tolerances and advanced materials on the newer lamps should offer a better lamp to dim. On the other
hand, a larger
globe should offer more stabilization to the inner capsule of the lamp while dimming in making the effects of heat on the lamp take place over a longer period of time and is more stable under things like a
voltage spike, or lack of forced cooling.
So it’s up to question and study perhaps on what would be more efficient in a lamp not designed to dim to be dimmed.
(I forget the source but it’s a detail that can be important
“
THD = Total Harmonic
Distortion - A measure of the
distortion of the
sine wave on
alternating current (ac) systems caused by higher order waves superimposed on the fundamental (usually 60 Hz.) frequency of the
system.
THD is expressed in percent and may refer to individual electrical loads (such as a
ballast) or total electrical
circuit or
system in a building. The
ANSI recommendation is for
THD to be no greater than 32% although some electrical utilities may require lower
THD’s on some systems. Excessive
THD’s on electrical systems can cause efficiency losses as well as overheating and deterioration of
system components.”
Maintaining internal lamp pressure and the arc are going to be two large problems which ever type of dimming is done and dependant upon the
transformer type which might in combination hurt or help this process. Most of the above
hot restrike lamps can be dimmed with either a magnetic or electronic
ballast but the magnetic
ballast should be easier to work with at very least in dealing with the added
power consumption as the luminous output goes down.
Also a note that while not specific to this, something that could be of interest out of the free Osram PDF: Technology and Application,
Metal Halide Lamps Photo Optics.
“Operating Conditions:
Metal Halide lamps are operated on ac
voltage which is supplied by chokes or high-reactance transformers or by electronic control gear. Electronic control gear operates with a constant output and ensure flicker-free light. In the clod state,
metal halide lamps, like all discharge lamps, are excellent insulators and have to be made conductive with a high-voltage discharge (ignition). Whereas only a few kilovolts are needed to ignite a cold lamp, pulse voltages ten times higher are required for hot restarting.”
Also a small detail that might be important:
“What currently does adversely affect the lamp life is switching the lamp off while it is still in start-up
phase because the filler components are deposited on the internal wall of the
bulb and on the electrodes. This impairs both restart behavior and life expectancy.”
Letting the lamp warm up sufficiently before you start dimming it is probably going to be a very good idea. Also a side note from Philips on
hot restrike lamps, “Operation of the lamp at voltages greater than 106% of nominal value could damage the lamp.”
Another interesting free PDF article might be: from Osram. Guidelines for control gear and igniters Xenon Short Arc Lamps Photo Optics, Technology and applications XBO theater lamps, Manufacturers of control gear and igniters for special discharge lamps.
And finally some notes directly on the subject:
“Dimming of
HMI Metal Halide Lamps: Dimming = operation of the lamp at less than rated
power with reduced light output. In this age of flexibility, there is an increasing demand for light which can be individually dosed according to the particular application. The ideal solution would be the “rubber lamp” which could “stretch” across a wide range of wattages with no loss of photometric quality. It is this loss of quality which is the prime concern when we consider dimming
metal halide lamps. You may recall the rule of thumb from
tungsten-halogen lamps that a 5%
drop in
voltage will double the life and reduce the color temper as
power decreases: discharge lamps behave in a similar way, initially at least.
As you would expect, dimming causes a
drop in luminous flux - as is the case with
tungsten halogen lamps. The
color temperature however, increases (i.e. the lamp appears more “blueish”), while color
rendering (
CRI) deteriorates as
power input decreases. The metals, which are responsible for the red component in the spectrum, are the last of the filter components to vaporise during startup and the first to condense out again when the lamp is dimmed. They are therfore no longer available for generating light. The result is that the light appears more “blueish.” The loss of the red component also means poorer color
rendering. The reason why the filter components start to condense again is the
drop of the
bulb temperature at lower wattages.
These effects can be avoided by regulating the amount of light which grey scale filters or mechanical shutters. The lamp continues to operate at full load, so its photometric properties remain more or less unaffected at every
stage. If the lamp is dimmed by
electric means it will not reach its optimum operating state and, unlike
tungsten-halogen lamps, will not last longer. The best possible operating mode for a
metal halide lamp is when it is operated at rated wattage.
Dimming is certainly useful for mobile news reporting teams who are reliant on batteries and will want to operate the lamps at full load only for actual shoots and otherwise stay in
standby mode to save energy and reduce the startup time to a minimum.
The temperature of the
bulb wall falls more rapidly on a lamp without an outer
bulb than on a lamp with an outer in which the discharge tube can only be influenced by the temperature surrounding the lamp indirectly or at least with a long
lag time. In terms of dimming, outer
bulb lamps are therefore not as sensitive and react more favourably to reductions in wattage with respect to changes in their color quality.
Forced cooling can
attenuate temperature-related problems but it cannot eliminate them.
(Osram Photo-Optic Lighting Products Catalog - 1999)”
“Boosting
Power to HMP lamps: Boosting = operation of the lamp at more than the rated
power with increased light output. We strongly advise you do not consider boosting
metal halide lamps (i.e. operating them at overloads) unless the lamps are expressly approved for this purpose. From the photometric
point of view, the effects of boosting are virtually the opposite of the effects of dimming: color
rendering is improved and the
color temperature drops. The increased load on the electrodes and the higher temperatures at the molybdenum foils and on the
bulb walls will most probably lead to premature failure of the lamp.
With regard to boosting, the HMP range of lamps is currently an exception. They have been developed and approved specifically for “boosting operation”. Depending on the particular model, the lamps can be operated up to 1.5 times their rated wattage. At these high wattages, a reduction of up to 50% in lamp life can be expected. What we said about dimming also applies to boosting:
metal halide lamps operate best at rated wattage. Users in the (overhead) projection sector readily accept this shorter lamp life in view of overwhelming advantages of boosted operation. At presentations which make use of
LCD panels and traditional transparencies the ability to regulate the output of HMP lamps is of considerable value: reduced (dimmed) output (down to 50%) for the transparencies with reduced glare for the
presenter and increased (boosted) output (up to 150%) for the
LCD panels which because of their poor efficiency require as much light as possible.
Since the two forms are often used alternately during actual presentations, the problem of shorter lamp life is unlikely toarise, particularly considering the fact that HMP lamps naturally have a service life which is around 33% longer than comparable
HMI models. With the
introduction of HMP technology. Osram has succeeded in presenting a range of lamps which has been optimised for projection applications.
(Osram Photo-Optic Lighting Products Catalog - 1999)”
MARTIN TECHNICAL NEWS
No. 352
2005-03-21
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USER SUPPORT BULLETINS
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1) Atomic 3000 Can Cause
Voltage Drops
We have seen a number of cases of fixtures resetting intermittently
when connected to the same AC
circuit as Atomic 3000's.
The Atomic 3000 can draw up to 33 A. The heavy
current consumption can
cause a short
voltage drop that is large enough to disrupt the 5V
power
supply in other products like the
MAC 2000. If this happens, the
fixture's main
processor drops out and then reboots when the
voltage
comes back up, causing the
fixture to reset.
To avoid this situation, we recommend powering Atomic 3000s on their
own separate AC feed. If this is not
practical, we we recommend using
the Atomic 3000 in low
power mode, with DIPP-switch 6 "ON".
__________________________GE Lighting Institute
High
Intensity Discharge Lamp Dimming
There is an increasing demand to maximize energy savings of lighting sources. While
HID lamps are inherently very efficient, many users would like to further increase the energy savings of
HID lamps through dimming.
There are two general classes of
HID dimming systems. In bi-level dimming,
HID lamps are run in a low mode of reduced lamp
power when less light is required. Lamps are then switched to 100% lamp
power (high mode) when full illumination is needed. The other common class of dimming systems is called “continuous” and allows for user settings from 0% to 100% wattage, and thus, complete light control.
This dimming statement is valid for any kind of dimming
system that meets the stated criteria. In general, most bi-level dimming systems meet the criteria, while many of the continuous dimming systems do not.
GE Lighting will warrant its
mercury vapor lamps, Multi-Vapor®, PulseArc™, stayBright®
metal halide lamps and Lucalox® high pressure sodium lamps on bi-level or continuous dimming systems provided the following operational guidelines, in addition to those provided on the lamp packaging and in the GE 9200 lamp catalog, are met:
Multi-Vapor®, PulseArc™, and Watt-Miser®, stayBright®
metal halide Lamps :
ChromaFit™ HPS retrofit Lamps:
Vertical
base up (+/-15°) operation only for all types, except for the MVR1000/U which can be operated in vertical
base up (+/-15°) to horizontal (+/-15̊) positions when dimmed per the approved guidelines indicated within this document.
Open or enclosed fixtures for 360, 400, 750 and 1000-watt standard and high-output lamps; Enclosed fixtures only for 175, 320, 250, 1500
watt and compact lamps. For other lamp wattages, see the “General Comments.”
Lamp must be started in full-power mode and must be operated in that mode for a minimum of fifteen minutes prior to reduced-power operation.
Minimum open
circuit voltage (OCV) of dimming
system must meet
ANSI requirements in both high or low modes of operation (see appropriate
ANSI C78.xxxx documents for specific
metal halide lamp minimum OCV requirements.)
Minimum lamp operating wattage as indicated in the following table. If operated below these wattages, the bimetal
switch that normally shorts the main and starting electrodes in standard type lamps may not function properly, and this could result in rupture of the arc tube. PulseArc™ lamps do not utilize a bimetal
switch and may also be dimmed as specified below.
Lamp
Power Rating Minimum Lamp Operating
Power Watts)
(watts) (see “General Comments,” item 2)
150 watts (Watt-Miser®) 97 watts
175 watts 97 watts
320 watts 138 watts
250 watts (including ChromaFit™) 138 watts
360 watts (Watt-Miser®) 200 watts
400 watts (including ChromaFit™) 200 watts
750 watts 375 watts
1000 watts 500 watts
1500 watts 750 watts
Mercury Vapor Lamps
All guidelines listed for
metal halide lamps in the previous section also apply for
mercury vapor lamps.
Lucalox® High Pressure Sodium Lamps:
Any burning position is allowed.
Open and enclosed fixtures are allowable.
Minimum open
circuit voltage (OCV) of dimming
system must meet
ANSI requirements in both high and low modes of operation (see appropriate
ANSI C78.xxxx documents for specific high pressure sodium lamp minimum OCV requirements.)Lucalox® High Pressure Sodium Lamps:
Lamps must be operated in the full-power mode for at least fifteen minutes prior to operation in the reduced-power mode.
For dimming systems which reduce
line voltage (which can affect the
ANSI open
circuit voltage value), it is important to reduce the
line voltage slowly to avoid premature lamp cycling, especially with older lamps that are already high in
voltage and close to the normal drop-out
point. In changing from the full-power mode to the reduced-power mode, the time between full
power and reduced
power must be no less than ninety seconds, and the rate of change of
power at any
power level between full
power and reduced
power must be no greater than that corresponding to a linear (uniform) reduction between those extremes in a ninety-second time interval.
For dimming systems that instantaneously
switch capacitors into the
system, but retain the
ANSI ballast OCV value at all times, normal lamp performance can be expected.
Minimum lamp operating wattage for all standard and deluxe high pressure sodium lamps are indicated in the following table.
Lamp
Power Rating Minimum Lamp Operating
Power (Watts)
(watts) (see “General Comments,” item 2)
35 watts 13 watts
50 watts 18 watts
70 watts 25 watts
95 watts 34 watts
100 watts 35 watts
110 watts 39 watts
125 watts 44 watts
150 watts 53 watts
200 watts 70 watts
215 watts 76 watts
250 watts 88 watts
310 watts 109 watts
360 watts 126 watts
400 watts 140 watts
750 watts 263 watts
1000 watts 350 watts
General Comments
Saf-T-Gard® lamps must not be used in dimming systems.
The effects of
line voltage fluctuation,
ballast wattage control and lamp operating
voltage variation within the range of the
ANSI specifications must be considered so that no combination of factors causes the lamp
power to go below the specified limits.
HID lamps should not be held in the dimmed mode for extended periods of time. Periodic cycling to full
power is required.
Rated life of
HID lamps is the total burning time in dimmed and full-power modes.
GE Lighting warrants life, lumens and
lumen maintenance will meet published
rating performance on bi-level or continuous dimming systems provided the foregoing guidelines are met. Performance criteria such as CCX, CCY,
CCT and
CRI may vary from specification when lamps are used at lower than full-wattage mode. Lamp
efficacy will be lower in dimmed modes than in full-power mode.
The dimming device should maintain the lamp
current crest factor,
current off time and
line dip tolerance, as well as the open
circuit voltage, within
ANSI and
IEC specifications at all operating levels of the lamp.
Lamps that were not specifically mentioned include the 325-watt
metal halide lamp, low-wattage metal lamps (<175 watts) and all
metal halide lamps burned outside the vertical
base up +/- 15̊ position, except for the MVR1000/U which is approved for dimming when operated in vertical
base up +/- 15̊ to horizontal +/- 15̊ burning position as stated within. Guidelines for using these lamps on dimming systems may be published at a later date.
GE Lighting Institute
www.gelighting.com
Rev. 10/9/01