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Name: Nicholas
Status: other
Grade: 12+
Location: NY
Country: USA
Date: N/A 


Question:
The greenhouse effect (not an environmental reference, but an actual greenhouse, made out of glass) is very efficient at retaining infra-red light which heats the house. Does Plexiglas have the same infra-red retention capabilities? If so, what is the common ground between the two very different materials that provides this ability?



Replies:
Nicholas,

Greenhouses actually work by a somewhat different mechanism than the environmental greenhouse effect. Although there is some trapping of infrared, greenhouses primarily work by allowing visible light in (for which glass or Plexiglass or even plastic sheeting can be made transparent), as the light is absorbed by the environment (plants and ground), energy is radiated out (convection) in the form of heat. The heat is then trapped by the greenhouse structure. There is some energy transmitted in the form of infrared, but this is minor as can be shown by simply opening a small window on the roof of a greenhouse and noting that the temperature within drops considerably (more than can be accounted for by escaping infrared). Thus, the only requirement for greenhouse material is that it be transparent to visible light, and be sealed so that convection is maintained within the structure. Additional considerations such as infrared reflectiveness, roof angles, and conduction can be addressed for efficiency purposes, but are less important.

Greg (Roberto Gregorius)
Canisius College



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