if glass is a bad conductor of heat, how does it let the heat of sunlight enter in a greenhouse?

Asked by  | 24th Sep, 2008, 10:56: PM

Expert Answer:

Glass does not conduct heat through it. Glass is a good conductor of heat when it is found in fiberglass. Glass allows radiant heat to pass through freely. The reason that glass is such a valuable material is that it exhibits a very low absorption of electromagnetic radiation in the visible range.

The glass panels of greenhouse let in light but keep heat from escaping. A pane of transparent glass allows solar radiation to pass through, but interferes with the convection that would let heat out. In a greenhouse, the temperature is relatively warmer than the outside air temperature.  The glass walls enable the sun's energy to stream in, however,they also prevent the converted heat energy from escaping. The longer infrared wavelengths radiated by sun-warmed objects do not pass readily through the glass. The entrapment of this energy warms the interior of the vehicle or greenhouse. The trapping of the hot air so that it cannot rise and lose the energy by convection also plays a major role.

Short wavelengths of visible light are readily transmitted through the transparent glass. Shorter wavelengths of ultraviolet light are largely blocked by glass since they have greater quantum energies which have absorption mechanisms in the glass. 

Answered by  | 25th Sep, 2008, 07:23: AM

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