| Comparison of Power Conversion of White Light Sources
All light sources convert electric power into radiant energy and heat in various proportions. Incandescent lamps emit primarily infrared (IR), with a small amount of visible light. Fluorescent and metal halide sources convert a higher proportion of the energy into visible light, but also emit IR, ultraviolet (UV), and heat. LEDs generate little or no IR or UV, but convert only 15%-25% of the power into visible light; the remainder is converted to heat that must be conducted from the LED die to the underlying circuit board and heat sinks, housings, or luminaire frame elements. The table below shows the approximate proportions in which each watt of input power is converted to heat and radiant energy (including visible light) for various white light sources.
Power Conversion for “White” Light Sources |
| |
Incandescent†
(60W) |
Fluorescent†
(Typical linear CW) |
Metal Halide‡ |
LED* |
| Visible Light |
8% |
21% |
27% |
15-25% |
| IR |
|
37% |
17% |
~0% |
| UV |
0% |
0% |
19% |
0% |
| Total Radiant Energy |
81% |
58% |
63% |
15-25% |
Heat
(Conduction + Convection) |
19% |
42% |
37% |
75-85% |
| Total |
100% |
100% |
100% |
100% |
† IESNA Handbook ‡ Osram Sylvania
* Varies depending on LED efficacy. This range represents best currently available technology in color temperatures from warm to cool. DOE’s SSL Multi-Year Program Plan (March 2006) calls for increasing extraction efficiency to more than 50% by 2012.
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