Re: Light output of dimmed lamps


"CJT" <abujlehc@xxxxxxxxxxx> wrote in message
news:43AC8193.8050309@xxxxxxxxxxxxxx
> Can anybody point me to some information about how the light output of
> incandescent and halogen lamps varies as they are dimmed? I'd like to
> compare the efficiency of a high-wattage bulb when dimmed to lower
> wattage bulbs operated full-on.

Best place to find the information is the Illuminating Engineering Society
Handbook (any edition); but it's not on-line. You can usually find a copy
in a good reference library, however.

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.

Take a look at:
http://www.sylvaniaautocatalog.com/new_sylvania/tung_fila_lamps.htm to see
the curves. The values there apply to low voltage automotive, but the
numbers for 120 volt lamps aren't much different.

Since efficiency drops faster than light output when incandescent bulbs are
dimmed, dimming is not a good energy-saving strategy. At best, incandescent
bulbs only emit 10% of their power input as light anyway.

Variable autotransformer dimmers were never widely used for residential
lighting, but they were indeed used. Residential versions were made by the
Superior Electric Co. in the 1950s and 60s. If you happen to see some
reruns of the TV show "Frasier", you'll see several of them on the wall of
his radio studio. The have rather large control knobs -- about 4 in. in
diameter and required a wall box that is about 4 times the size of a
standard box.

TKM


.

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