All light sources convert electric power into light and heat in various proportions. Incandescent bulbs emit mainly in infrared (IR) region with only approx. 8% of light emitted. Fluorescents emit higher portion of light (21%) but also emit IR, UV, and heat. LEDs generate little IR and convert up to 40% of the electrical power into the light (see Figure 3.3.1). The rest is converted to heat that must be conducted from the LED active area to the underlying printed circuit board, cooling system, housing, and atmosphere.
Figure 3.3.1: Power conversion rates for “White” Light Sources.
In case of LED light source, there is no heat removal by thermal radiation, thus dissipative heat has to be withdrawn only by conduction and convention. However LED has the best efficacy, thermal management of this light source is the most challenging and proper design of cooling system is crucial for LED-based luminaire.