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About projector bulbs

M

Markus

Jan 1, 1970
0
Few questions about lcd projectors and bulbs used in these:

How does metal halide bulb used in LCD-projector acts when it's life
time is over? Does it burn out instantaneously like normal glow bulb or
does it dim out step-by-step?

How does projector know when to bulb is burnt out? Is it possible to
measure or test metal halide bulb someway?

I know that ignition voltages can be very high (kV). Is there way to
measure if projector is trying to ignite bulb at all?

-markus
 
V

Victor Roberts

Jan 1, 1970
0
Few questions about lcd projectors and bulbs used in these:

How does metal halide bulb used in LCD-projector acts when it's life
time is over? Does it burn out instantaneously like normal glow bulb or
does it dim out step-by-step?

It does not light or else it explodes. While metal halide
lamps may dim over life, this is a very gradual process that
starts when the lamp is first operated. The lamp does not
dim in such a way that the dimming can be used to predict
the time when the lamp will fail to start.
How does projector know when to bulb is burnt out? Is it possible to
measure or test metal halide bulb someway?

It doesn't light. If the projector doesn't sense that the
lamp has not started the operator certainly will.
I know that ignition voltages can be very high (kV). Is there way to
measure if projector is trying to ignite bulb at all?

Not without proper high voltage measurement equipment and
some way to override the interlock that prevents (or should
prevent) the ballast from operating when the lamp
compartment is open.

Since you cannot predict lamp failure, you should always
have a spare bulb available and that spare can be used to
confirm that the original has failed.

--
Vic Roberts
http://www.RobertsResearchInc.com
To reply via e-mail:
replace xxx with vdr in the Reply to: address
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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.
 
S

SimonLW

Jan 1, 1970
0
Markus said:
Few questions about lcd projectors and bulbs used in these:

How does metal halide bulb used in LCD-projector acts when it's life time
is over? Does it burn out instantaneously like normal glow bulb or does it
dim out step-by-step?

How does projector know when to bulb is burnt out? Is it possible to
measure or test metal halide bulb someway?

I know that ignition voltages can be very high (kV). Is there way to
measure if projector is trying to ignite bulb at all?

-markus
Most bulbs used in projectors are ultra high pressure (UHP) mercury types.
They claim to lose less lumens over their life time, but I don't know the
failure mode. Does your projector claim to use MH? MH tends to get dim.

Some projectors have an hour counter that tracks usage time and may
recommend a bulb replacement after so many hours. Others may have circuitry
in the ballast to check if the bulb is starting or not. It depends on the
unit.

Playing with HV can get you hurt or at least give you a big jolt. I
recommend having a trained technician look at it. They have the proper tools
to check for pulsed HV.

-S
 
J

James Hooker

Jan 1, 1970
0
The lumens of the UHP Mercury lamps in fact stay pretty constant over time,
there is no blackening of the arc tube. However the projected screen lumens
do decrease, and what eventually kills these lamps is devitrification of the
quartz. The quartz will go opaque due to a crystallisation process, and
then it scatters the light produced by the arc, so that less of the light is
focussed into the projected beam.

The crystallised quartz is considerably weaker than in a new lamp, and
sooner or later the arc tube will explode. This is not so bad as it might
sound, the arc tube is so tiny that the total amount of energy released is
minimal. The mercury vapour released into the atmosphere is instantly
oxidised and rendered safer. The projector has a built-in clock and will
usually tell you when lamp life has exceeded 1000 hours or whatever, as an
indication that failure is imminent. The Iwasaki lamps seem to have
superior performance, where they have been somewhat successful in creating
an arc tube which is far less likely to suffer this end of life explosion
failure.

James.
 
T

TKM

Jan 1, 1970
0
James Hooker said:
The lumens of the UHP Mercury lamps in fact stay pretty constant over
time, there is no blackening of the arc tube. However the projected
screen lumens do decrease, and what eventually kills these lamps is
devitrification of the quartz. The quartz will go opaque due to a
crystallisation process, and then it scatters the light produced by the
arc, so that less of the light is focussed into the projected beam.

The crystallised quartz is considerably weaker than in a new lamp, and
sooner or later the arc tube will explode. This is not so bad as it might
sound, the arc tube is so tiny that the total amount of energy released is
minimal. The mercury vapour released into the atmosphere is instantly
oxidised and rendered safer. The projector has a built-in clock and will
usually tell you when lamp life has exceeded 1000 hours or whatever, as an
indication that failure is imminent. The Iwasaki lamps seem to have
superior performance, where they have been somewhat successful in creating
an arc tube which is far less likely to suffer this end of life explosion
failure.

James.

This is good information, James, thanks. I've been wondering if there is
much difference among brands. As the lamp in my projector reaches eol, do
you know of any lamps that have enhanced red output? Mercury lamps, of
course, emit very little in the red end of the spectrum anyway; but I've
been very disappointed with the color of UHP lamps compared to even poor
computer screens.

Terry McGowan
 
V

Victor Roberts

Jan 1, 1970
0
This is good information, James, thanks. I've been wondering if there is
much difference among brands. As the lamp in my projector reaches eol, do
you know of any lamps that have enhanced red output? Mercury lamps, of
course, emit very little in the red end of the spectrum anyway; but I've
been very disappointed with the color of UHP lamps compared to even poor
computer screens.

UHP lamps are run at very high pressure, > 200 atm, for the
express purpose of generating red light. See Figure 3 of
US 5,109,181, the original Philips UHP patent. However, I
agree that it is still hard to get the same level of
saturated red that you can get with an LCD screen lit with
good fluorescent lamps.

--
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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