The Greenhouse Effect

Window glass transmits visible light but it does not transmit infrared radiation. Light from the sun readily passes through a window. Objects inside a sunlit room absorb the solar radiation. They, in turn, emit radiation, but the radiation emitted is infrared rather than visible light. The infrared radiation cannot penetrate the window. (Visible light can be red, orange, yellow, green, blue or violet; when these colors are mixed together, as in sunlight, we often call it "white light.")

So a window is a one-way street for heat transfer by radiation involving sunlight. A greenhouse, in part, uses this principle to provide a warm environment for plants. The overall process by which radiant heat energy is trapped has thereby come to be called "the greenhouse effect". The trapping occurs because heat radiation is charged from one wavelength to another, from visible light to infrared light.

The greenhouse effect in a house with large windows often makes the house too hot. In winter, it may be possible to use the greenhouse effect to advantage to help home heating.