Light output of dimmed lamps

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Somehow that seems unlikely, since incandescents are so non-linear.

That looks like the rms value of the rectified sine wave. If 120 = sqr(2V^2), V = 85.85 for half the waveform.
Nick
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TKM ( snipped-for-privacy@no.net) said...

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.
--
Calvin Henry-Cotnam
"Never ascribe to malice what can equally be explained by incompetence."
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Calvin Henry-Cotnam wrote:

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
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Jeffry Wisnia

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I remember one night working with the properties of tungsten table and a few voltage and current reading I got from a 120V 100 watt "A19" 750 hour lamp, and working out a "rough 1-size-fits-all" rule for color temperature as a function of applied voltage. I figured color temperature being roughly proportional to voltage to the .375 power (square root 3 times and cube the result). Somehow I think a 750 hour 100W 120V bulb at full voltage has a color temperature of about 2850 Kelvin. At 71% of full voltage (when it would draw about 60 watts) its color temp. would then be about 2500 Kelvin.
- Don Klipstein ( snipped-for-privacy@misty.com)
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I remember one night working with the properties of tungsten table and a few voltage and current reading I got from a 120V 100 watt "A19" 750 hour lamp, and working out a "rough 1-size-fits-all" rule for color temperature as a function of applied voltage. I figured color temperature being roughly proportional to voltage to the .375 power (square root 3 times and cube the result). Somehow I think a 750 hour 100W 120V bulb at full voltage has a color temperature of about 2850 Kelvin. At 71% of full voltage (when it would draw about 60 watts) its color temp. would then be about 2506 Kelvin.
And in a chart in the page pointed out by Terry McGowan, http://www.sylvaniaautocatalog.com/new_sylvania/tung_fila_lamps.htm , color temperature is said to be proportional to voltage to the .42 power. This means that a 100 watt 120V 750 hour lightbulb, if 2850K at full voltage, would have a color temperature of about 2468 K at 71% of full voltage (where it would draw nearly 60 watts and achieve about 31% of full light output).
- Don Klipstein ( snipped-for-privacy@misty.com)
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Now that I have a break from work for a few days, I had some spare time to check back on and refine this. Instead of .375 for a "color temperature exponent", I now get .39. That changes my 2506 K at 71% of full voltage to 2494 K. In addition, I worked out a "light output exponent" of 3.5 for this 100 watt A19 over the 84-120V range. Light output at 71% of full voltage would be 30% of that at full voltage - roughly!

My findings for 100 watt 120V 750 hour A19 today: Current at 84 volts is 82.5% of that at 120 volts. The "current exponent" is .54. Power consumption at 71% of full voltage would be .71 to the 1.54, or 59% of full power. Energy efficiency is aroughly 51% of that at full power.
Lower wattage gas-filled 120V incandescent lamps will have current and power consumption varying slightly less, and color temperature and light output varying slightly more with voltage. I found a 25 watt gas-filled A19 to at 84 volts draw 83.5% of current at 120 volts, for a "current exponent" of .504. At 71% of full voltage, it would consume 59.7% of full power. I expect 60 watt ones to be a little more like 100 watt ones than like 25 watt ones for their exponents.
Meanwhile, a vacuum incandescent lamp (25 watt T10) at 84 volts consumed 81.1% as much current as at 120 volts. That makes the "current exponent" .588. Power consumption at 71% of full voltage would be 58% of that at full voltage.
- Don Klipstein ( snipped-for-privacy@misty.com)
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TKM wrote:

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TKM wrote:

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