A greenhouse uses a special kind of glass that acts as a medium which selectively transmits
spectral frequencies. Spectral comes from the word “spectrum”.
In layman's terms, a spectral frequency can be defined in terms of the following principle: any
object in the universe emits, radiates or transmits light. The distribution of this light along an
electromagnetic spectrum is determined by the object's composition.
Therefore, the glass of a greenhouse traps energy within the greenhouse and the heat in turn
provides heat for the plants and the ground inside the greenhouse. It warms the air near the
ground, preventing it from rising and leaving the confines of the structure.