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Metal Halide Lamps

V

Victor Roberts

Jan 1, 1970
0
I've had some tests run on metal halide lamps by a certified
independent laboratory (since I don't have a sphere.) The
main goal of this work was to quantify the high frequency
efficacy of metal halide lamps. The common wisdom is that
there is no high frequency efficacy gain, but there are one
or two papers that claim otherwise. This is my poster paper
for LS:11.

The results are in and they are a bit strange.

The tests were run on three 320-watt pulse start metal
halide lamps. there is more money from the sponsoring
organization to run 6 more 320-watt lamps if necessary.

As part of the test I measured lamp performance on five
types ballasts:

1) Standard reference ballast
2) Commercial linear inductor ballast
3) Commercial CWA ballast
4) Brand A 100 kHz electronic ballast
5) Brand B 100 KHz electronic ballast.

There were three of each type of commercial ballast.

Since I suspected that the commercial ballasts would not all
run the lamp at the same power, and since lamp efficacy is a
function of power, I had the lab operate the lamp on the
reference ballast at rated power, rated power + 15% and
rated power -15%, so I could construct a correction curve.

The really strange result is that lamp efficacy on both
types of commercial ballasts was lower than on the reference
ballast, even after correcting for the fact that the
commercial ballasts ran the lamp below rated power. The
corrected efficacy loss is about 6% to 7%. The only
explanation I have right now is that these lamps have lower
efficacy when operated with a high current crest factor
system. I don't see any other obvious difference between
lamp operation on the reference ballast and on the
commercial ballasts that operate the lamps at the same
frequency.

Any other suggestions for a cause?

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.
 
J

JB

Jan 1, 1970
0
Victor Roberts said:
I've had some tests run on metal halide lamps by a certified
independent laboratory (since I don't have a sphere.) The
main goal of this work was to quantify the high frequency
efficacy of metal halide lamps. The common wisdom is that
there is no high frequency efficacy gain, but there are one
or two papers that claim otherwise. This is my poster paper
for LS:11.

The single biggest improvement I've seen when operating MH lamps at high
frequencies, and especially ceramic metal halides, is lamp to lamp colour
variation reduction. With some ballasts I have here we are talking _single_
digit °K colour temperature variance between a group of 10 lamps when
operated on 500kHz+ pure sinewave ballasts. Even the engineers at GE's
Leicester labs here in the UK were amazed at this effect. Also the arc
itself becomes more 'constricted' (very visible if you project the arc image
from a quartz burner through a large projection lens onto a wall) and also
far more stable at these frequencies.

Another most unusual effect again not predicted, was an overall general
reduction in CCT of ceramic lamps with increasing frequency (above ~325kHz).
Typical 3000°K CMH/CDM lamps would have a CCT nearer to 2850°K operating at
exactly the same lamp power as on normal electromagnetic ballasts or even
sub-200Hz squarewave electronic ballasts.

I put many tens of thousands of burning hours on various 20-400W MH and
70-400W SON lamps operating from a variety of high frequency sinewave
ballasts over the course of about 8 years, partly as part of a ballast
development program but also out of curiosity/interest. This is still a
very, very interesting area of research for me. I'm quite lucky with the
resources in my lab here in the UK too, as I've just recently finished
building a 3M diameter sphere with both a spectrometer and luminous flux
measurement system installed.

Let me know if you'd like a few ballast samples to play with. I have some
70W and 150W in dual voltage 120/240V versions here.


<snip>


JB
 
T

TKM

Jan 1, 1970
0
Victor Roberts said:
I've had some tests run on metal halide lamps by a certified
independent laboratory (since I don't have a sphere.) The
main goal of this work was to quantify the high frequency
efficacy of metal halide lamps. The common wisdom is that
there is no high frequency efficacy gain, but there are one
or two papers that claim otherwise. This is my poster paper
for LS:11.

The results are in and they are a bit strange.

The tests were run on three 320-watt pulse start metal
halide lamps. there is more money from the sponsoring
organization to run 6 more 320-watt lamps if necessary.

As part of the test I measured lamp performance on five
types ballasts:

1) Standard reference ballast
2) Commercial linear inductor ballast
3) Commercial CWA ballast
4) Brand A 100 kHz electronic ballast
5) Brand B 100 KHz electronic ballast.

There were three of each type of commercial ballast.

Since I suspected that the commercial ballasts would not all
run the lamp at the same power, and since lamp efficacy is a
function of power, I had the lab operate the lamp on the
reference ballast at rated power, rated power + 15% and
rated power -15%, so I could construct a correction curve.

The really strange result is that lamp efficacy on both
types of commercial ballasts was lower than on the reference
ballast, even after correcting for the fact that the
commercial ballasts ran the lamp below rated power. The
corrected efficacy loss is about 6% to 7%. The only
explanation I have right now is that these lamps have lower
efficacy when operated with a high current crest factor
system. I don't see any other obvious difference between
lamp operation on the reference ballast and on the
commercial ballasts that operate the lamps at the same
frequency.

Any other suggestions for a cause?

From what I recall, Vic, your crest factor idea is correct. I would go
further, however, and suggest that the shape of the lamp current wave is the
controlling factor, not just the crest factor. I'm not a lamp scientist, of
course, but I do remember that Gil Reiling (and several other MH lamp
engineers) spent substantial time looking at tuning the lamp current
waveforms and then designing the ballasts to match those requirements.
Optimum waveforms changed with the metal halide mixture too.

It made sense to me because we were seeing something similar with
fluorescent lamps -- tune the timing and shape of the starting current and
voltage waveforms (what's now called the "starting scenario") and you end up
with a system where starting doesn't affect lamp life.

I've often thought that electronic ballasts could well give us the way to
optimize waveforms so as to improve several aspects of lamp performance and
that we should build an "optimize" control into the ballast to better match
the lamp and the ballast being used just as we now build in automatic
voltage sensing.

It's good to hear that you're looking a MH lamp efficacy as a function of
frequency. That's certainly been a long-debated question.

Terry McGowan
 
D

Don Klipstein

Jan 1, 1970
0
I've had some tests run on metal halide lamps by a certified
independent laboratory (since I don't have a sphere.) The
main goal of this work was to quantify the high frequency
efficacy of metal halide lamps. The common wisdom is that
there is no high frequency efficacy gain, but there are one
or two papers that claim otherwise. This is my poster paper
for LS:11.

The results are in and they are a bit strange.

The tests were run on three 320-watt pulse start metal
halide lamps. there is more money from the sponsoring
organization to run 6 more 320-watt lamps if necessary.

As part of the test I measured lamp performance on five
types ballasts:

1) Standard reference ballast
2) Commercial linear inductor ballast
3) Commercial CWA ballast
4) Brand A 100 kHz electronic ballast
5) Brand B 100 KHz electronic ballast.

There were three of each type of commercial ballast.

Since I suspected that the commercial ballasts would not all
run the lamp at the same power, and since lamp efficacy is a
function of power, I had the lab operate the lamp on the
reference ballast at rated power, rated power + 15% and
rated power -15%, so I could construct a correction curve.

The really strange result is that lamp efficacy on both
types of commercial ballasts was lower than on the reference
ballast, even after correcting for the fact that the
commercial ballasts ran the lamp below rated power. The
corrected efficacy loss is about 6% to 7%. The only
explanation I have right now is that these lamps have lower
efficacy when operated with a high current crest factor
system. I don't see any other obvious difference between
lamp operation on the reference ballast and on the
commercial ballasts that operate the lamps at the same
frequency.

Any other suggestions for a cause?

I would blame/credit current crest factor and not yet expect lower
current crest factor to help overall luminous efficacy in general.

In a given metal halide lamp with a given vapor composition (from a
given temperature of cold spot of inner surface of arc tube), lower
instantaneous current favors radiation from elements whose radiation
varies less with electron temperature (such as sodium) and higher
instantaneous current favors radiation from elements whose radiation
increases more drastically with electron temperature (such as mercury,
among MH lamp ingredients).

If the value for RMS current is decreased for a given power input, then
sodium (or thallium) radiation could get favored more over mercury
radiation. If the percentage of each half-cycle of the power line
frequency that has significant lamp current conduction increases, then
average and RMS current as determined over the significantly conducting
portion of each half-cycle of power line frequency decreases, then sodium
(or thallium) radiation could get more favored over that of mercury.

Furthermore, lack of cool moments in the arc twice per cycle of power
line frequency could increase the arc tube temperature, and increase the
concentration of vapors of the halides.

So if more sodium (or thallium) radiation and less mercury radiation
means more efficacy, I suspect making the power input to the arc more
constant throughout each half-cycle of the power line frequency can
achieve this.
I would watch for any higher arc tube temperature and any ill effects
thereof.
I would also look for a way to obtain spectral power distribution
results, and look for shifting towards visible emission features favored
by higher arc tube temperature, and away from any favored by higher
electron temperature, as a result of changing to the electronic ballast.

Now for another matter: High frequency electronic ballasts in
comparison to line frequency iron core ones are known to increase the
efficacy of fluorescent lamps via the following mechanisms:

1. Avoids some "saturation" (or approaching such) of shortwave UV
production of a low pressure mercury discharge, that results from peak
power input (whether absolutely or long enough to be a major fraction of
"imprisonment time") approaching the ability of the discharge to radiate
such an amount of power from a given discharge surface area, available
bandwidth of the desired spectral feature, and available from the electron
temperature (which for that matter usually decreases when power input to
fluorescent lamps increases IIUC).

2. Avoids the "oscillatory anode fall" (approx. 2.5 volts
largely not useful-radiation-producing voltage drop) that most fluorescent
lamps have when fed either DC or AC of frequency of frequency around or
less than 1 KHz. I am aware of some fluorescent lamps having an electrode
structure that impairs this loss in DC and low frequency use, but for now
I forget about any examples other than US Patent 4,902,933.

This makes me wonder if MH lamps or the ones in question have any
electrode-related voltage drops that are nonlinear (in a way where losses
can be reduced by lower current crest factor) or time dependent/
oscillatory in a way that can be mitigated by use of high frequency AC.

- Don Klipstein ([email protected])
 
V

Victor Roberts

Jan 1, 1970
0
I would blame/credit current crest factor and not yet expect lower
current crest factor to help overall luminous efficacy in general.

Well, I don't understand how, as a general rule, increasing
the crest factor can reduce efficacy while reducing it will
not increase efficacy. Why should a CCF of 1.414 always be
optimum?
In a given metal halide lamp with a given vapor composition (from a
given temperature of cold spot of inner surface of arc tube), lower
instantaneous current favors radiation from elements whose radiation
varies less with electron temperature (such as sodium) and higher
instantaneous current favors radiation from elements whose radiation
increases more drastically with electron temperature (such as mercury,
among MH lamp ingredients).

If the value for RMS current is decreased for a given power input, then
sodium (or thallium) radiation could get favored more over mercury
radiation. If the percentage of each half-cycle of the power line
frequency that has significant lamp current conduction increases, then
average and RMS current as determined over the significantly conducting
portion of each half-cycle of power line frequency decreases, then sodium
(or thallium) radiation could get more favored over that of mercury.

Furthermore, lack of cool moments in the arc twice per cycle of power
line frequency could increase the arc tube temperature, and increase the
concentration of vapors of the halides.

So if more sodium (or thallium) radiation and less mercury radiation
means more efficacy, I suspect making the power input to the arc more
constant throughout each half-cycle of the power line frequency can
achieve this.
I would watch for any higher arc tube temperature and any ill effects
thereof.
I would also look for a way to obtain spectral power distribution
results, and look for shifting towards visible emission features favored
by higher arc tube temperature, and away from any favored by higher
electron temperature, as a result of changing to the electronic ballast.

Now for another matter: High frequency electronic ballasts in
comparison to line frequency iron core ones are known to increase the
efficacy of fluorescent lamps via the following mechanisms:

1. Avoids some "saturation" (or approaching such) of shortwave UV
production of a low pressure mercury discharge, that results from peak
power input (whether absolutely or long enough to be a major fraction of
"imprisonment time") approaching the ability of the discharge to radiate
such an amount of power from a given discharge surface area, available
bandwidth of the desired spectral feature, and available from the electron
temperature (which for that matter usually decreases when power input to
fluorescent lamps increases IIUC).

2. Avoids the "oscillatory anode fall" (approx. 2.5 volts
largely not useful-radiation-producing voltage drop)

I always though that the anode fall was about 5 volts. When
an F-lamp that operates at 100 volts is switched to FULL
MODULATED high frequency, the efficacy gain is about 4.5%,
representing the reduction in anode fall (since the electron
temperature is still fully modulated.)
that most fluorescent
lamps have when fed either DC or AC of frequency of frequency around or
less than 1 KHz. I am aware of some fluorescent lamps having an electrode
structure that impairs this loss in DC and low frequency use, but for now
I forget about any examples other than US Patent 4,902,933.

One of my own :)
This makes me wonder if MH lamps or the ones in question have any
electrode-related voltage drops that are nonlinear (in a way where losses
can be reduced by lower current crest factor) or time dependent/
oscillatory in a way that can be mitigated by use of high frequency AC.

More work is needed to resolve this issue.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.
 
D

Don Klipstein

Jan 1, 1970
0
Well, I don't understand how, as a general rule, increasing
the crest factor can reduce efficacy while reducing it will
not increase efficacy. Why should a CCF of 1.414 always be
optimum?

I think my brain was running out of gas for the evening!

I now think that these particular lamps do appear to have efficacy
varying inversely with crest factor, and I doubt I meant to say that
improvement in efficacy only increases until crest factor drops to some
particular value.

I do suspect that some MH lamps may not have efficacy improved by lower
current crest factor.

- Don Klipstein ([email protected])
 
V

Victor Roberts

Jan 1, 1970
0
Vic,

This may sound like a very obvious question, but are you absolutely
sure that the power was measured correctly for doing the lamp
efficiency measurement? I've had a lot of problems in the past
measuring high powers at high frequencies. 100kHz in general is quite
high for a power meter. Also, most power meters specify their 3dB
bandwidth (which means there can be a factor two between reading and
actual value...)


Since I was not present I can't be sure of anything :), but
the lab is NAVLAP certified for metal halide lamp
measurements and the power meter they used has an accuracy
of about 1% at 100 kHz. The accuracy is specified in each
frequency band, it is not a 3db bandwidth. The lamp was
also connected to the power meter via a 4-wire Kelvin
connection, which is the right way to make the connection.

If Phase 2 is funded I plan to be at the lab when the
measurements are being taken. I visited the lab on a
previous occasion when they were making measurements for
another project I was working on, and was impressed with
their facilities and staff.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
or use e-mail address listed at the Web site.

This information is provided for educational purposes only.
It may not be used in any publication or posted on any Web
site without written permission.
 

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