Newsgroups: rec.arts.theatre.stagecraft
Subject: Re: Dimmers for Halogen Lights
References: <[email protected]>  
Richy Rich  writes:

> >> My wife is directing a shadow puppet piece.  I have two 500 watt
> >> halogen lights.  What can I use to dim these lights independently.  We
> >> are on a tight budget (are we ever not on a tight budget?) so cost is a
> >> factor.  Can I construct a box with wall dimmers you would find in
> >> Lowes or is there more to it?  Thanks for any input.
> 
> 
> Many wall dimmers do not seem to take kindly to Halogen lights even
> within their rating, check the inner packaging before buying as to the
> maker views for their model, I have a few in feature lighting round
> the office and they die even with 1/2 the rated load

What is the reason that many wall dimmers do not seem to take 
kindly to halogen lights ? 

The question what is so special in halogen lights ? 

I have dimmed 300W halogen bulbs (on 300/500W haloen flood light case) 
nicely with 350W wall dimmer (desienged for 230V 50 Hz AC). 
It has worked nicely. 

I can't see any specific what coudl be considerably different in 
diretly mains powered halogen bulbs and normal light bulbs 
what comes to the how dimmer sees them. To my understanding 
and based on my experiences there should not be any considerable 
difference to dimmer if the light bulb is halogen or not. 
It is a resistive load always, the resistance varies 
depeding on the bulb temperature (bulb takes quite high 
current briefly when it is turned on, that could be slightly 
higher with haloge bulbs I quess because higher temeprature 
difference between cold and full operating temperature where 
lamp takes its nominal current). 

The low voltage halogen system (those operatign at 12V or 24V) 
are entirely different story, because there is the need for 
some kind of transformer between mains and the bulb. 
This transformer could be a traditional transformer or 
electronic transformer. Both of those types are pretty 
different from pure resistive load, and the luck how well 
dimmer handles those varies (what dimmer is used and 
what kind of load). Generally if this works, the maximum 
load capacity of dimmer is reduced when drivign this kind 
of inductive/non-linear load like those low voltage 
halogen transformers are. If the dimmer + transformer 
system do not work well, the dimmign mysem becomes 
pretty useless and it is possible that the dimmer 
and/or the transformer gets damaged in the process.


-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/