Definition for word: Solar Heat Gain Coefficient

SHGC measures how well a window blocks solar heat. SHGC is expressed as a number between 0 and 1, and lower numbers indicate better blocking ability. Limiting solar heat gain is desirable in hot climates, but not in cold ones.

Referrence from

Solar gain (also known as solar heat gain or passive solar gain) refers to the increase in temperature in a space, object or structure that results from solar radiation. The amount of solar gain increases with the strength of the sun, and with the ability of any intervening material to transmit or resist the radiation.

Objects struck by sunlight absorb the short-wave radiation from the light and reradiate the heat at longer infrared wavelengths. Where there is a material or substance (such as glass) between the sun and the objects struck that is more transparent to the shorter wavelengths than the longer, then when the sun is shining the net result is an increase in temperature - solar gain. This effect, the greenhouse effect, so called due to the solar gain that is experienced behind the glass of a greenhouse, has since become well known in the context of global warming.

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