# Projectors and Line Voltage Fluctuations



## Prof. (Oct 20, 2006)

I've noticed now on several occasions, that my projected image appears brighter after about 10.30PM.!!

I'm guessing that after this time, most of the electricity useage from the surrounding areas has reduced..But would this have any affect on the lamp brightness?

Incandescent globes will dim with a lower voltage input, but I would have thought that once a mercury vapour lamp was struck, that it would remain constant even if there were some voltage variations..

I should also mention that I have a dedicated theatre that's just as dark at midday, so it's not that it's any darker outside at that time..


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## lcaillo (May 2, 2006)

Well, the ballast should maintain a constant current to the lamp, but the degree to which that is the case may vary. Many have little or no regulation on the supply voltage to the ballast and rely solely on the ballast to maintain lamp current constant.

The lamp will get brighter after it has been on a while, but that should not take a long time. Once the temp stabilizes the lamp should be pretty constant. There could be some thermal effects on the ballast, however.

Have you measured a difference or is it just a subjective impression?


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## Prof. (Oct 20, 2006)

It's just a subjective impression at the moment, but it's fairly obvious when it occurs..
I am plagued with a poor line voltage supply..being an outback country area...so much so that the house lights will dim slightly just turning on the electric kettle!! 

The projector would have been running for several hours before this happens..
Also the projector is well ventilated, mounted down from the ceiling, and with a ceiling exhaust fan immediately above it..

That being the case, it must be that the ballast is not providing any or very little stabilisation, to hold a constant current draw..


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## lcaillo (May 2, 2006)

I would not make assumptions until some measurements are recorded. Do you have a light meter? Subjective assessment of intensity is highly suspect and is mediated by many variables.


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## Prof. (Oct 20, 2006)

No I don't have a light meter..
What I really want to know is whether lamp output in most projectors, can be affected by voltage variations...and from what you've mentioned, it seems that it is possible for the lamp to increase in brightness, if other loads are removed from the line voltage, due to a non stabilised ballast.. ..


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## bassman_soundking (Nov 4, 2008)

Prof. said:


> No I don't have a light meter..
> What I really want to know is whether lamp output in most projectors, can be affected by voltage variations...and from what you've mentioned, it seems that it is possible for the lamp to increase in brightness, if other loads are removed from the line voltage, due to a non stabilised ballast.. ..


do you have a dedicated breaker to the theater or is it sharing one////(like mine  )?


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## Prof. (Oct 20, 2006)

No unfortunately..The whole house power supply is split between two breakers..
But when this variation occurs, there are no other appliances operating on the circuit that the HT is on..which makes me think it's other power draining equipment elsewhere..

Being a rural area, there are a lot of big water pumps and other industrial electrical equipment that run at different times..

My only alternative may be to get a Power Conditioner to stabilise the voltage to the HT room..


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## bassman_soundking (Nov 4, 2008)

If you can afford it I would go that route and get the power conditioner. There is nothing like a stable 120 to keep you gear around longer.


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## Prof. (Oct 20, 2006)

I may have to just grin and bare it for the moment..
The Conditioner I need is over $1000 here!!.


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## bassman_soundking (Nov 4, 2008)

yeah the ones that actually stabilize voltage are expensive!


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