Calvin Henry-Cotnam wrote:

TKM ) said...

The light output and power of an incandescent or halogen incandescent bulb
are exponential functions of the applied voltage. One point on the curve
that I remember is the half-power point. Say you operate a 100 watt bulb on
a dimmer at 50 watts, the light output is about 1/3 of full rated. When you
operate a bulb on a rectifier (diode) such as a high-low switch in the low
position, it operates at 1/2 power. As I recall, the measured voltage is
about 85 volts.


Another thing to consider when dimming an incandescent bulb (and I believe
halogens apply as well), is the spectral shift.

If you were to dim a 100 watt bulb so that it is only drawing 60 watts,
not only will its light output not be the same as the 60 watt bulb burning
fully, but the spectrum it puts out will be different.

What happens is that the lower temperature of the filament doesn't simply
lower the light output, but shifts some of it into the non-visible part of
the spectrum (the infra-red part: heat).

That 100 watt bulb that is dimmed so that it is only drawing 60 watts of
power will appear less bright and more red/orange in color than a 60 watt
bulb drawing its rated 60 watts.


Yep, and that's why I mounted a "hidden" dimmer with it's control shaft
(sans knob)sticking down through the top of the medicine cabinet in our
master bathroom. It's set a little bit down from full on and makes the
light from the bunch of 25 watt frosted globe bulbs around the mirror
redder than at full line voltage.

SWMBO likes it better for judging the appearance of the paint and stuff
the puts on her face, and I find it makes my own mug somewhat easier to
take on tough mornings.

As a plus, we've been here almost 20 years since I put that dimmer in
and I swear I haven't had to replace even one of the bulbs it's
controlling yet.

Happy Holidays!

Jeff

--
Jeffry Wisnia

(W1BSV + Brass Rat '57 EE)

"Truth exists; only falsehood has to be invented."