Re: X10 dimming

[Nigel Orr <nigel.orr@xxxxxxx>]

At 15:38 30/03/99 +0100, you wrote:
>I checked my halogen uplighter last night, and on it's dimmest setting
>the filament still glows slightly. This leaves me in a bit of a
quandry:
>either the dimmer is really clever and implements the 'pre-heat'
>facility Keith describes, thus prolonging the filament life

I'm a bit puzzled now- I used to do a lot of theatre lighting, and when the
bulbs were on preheat, you could usually see a dim glow.  But I thought
most theatre lights were halogen to get more output power- I never heard
any warnings about the effect on life of preheat though- do they assume
that some lampie will smash the bulb while handling it long before it's
life ends naturally?  Or is it just that in typical use every bulb on
preheat will run at full often enough to avoid problems?

I don't really have a 'feel' for how quickly the tungsten is deposited, or
how quickly it can be re-evaporated by running the light at full power, but
I would _guess_ that at low levels the tungsten is deposited very slowly
and at full power it is all re-evaporated very quickly.  So the problem
would only arise on a light that was _never_ run at full power.  There's
probably a 'worst case' of around 80% or something where the tungsten is
lost by the filament quickly but the temperature is too low to let it
re-deposit, but that's just an 'engineering guess'.

Anyone who would like to enlighten me on real details?

>I suppose I'll just have to suck it and see... Halogens aren't all that
>expensive for a one off experiment???

I would expect you'd have to do a _lot_ of experiments to get any sort of
usable results- I'm suspecting that in typical domestic use the effect
would be minimal...

Nigel
--
Nigel Orr                  Research Associate   O   ______
Underwater Acoustics Group,              o / o    \_/(
Dept of Electrical and Electronic Engineering     (_   <   _ (
University of Newcastle Upon Tyne             \______/ \(

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