ABSTRACT
This chapter explains radiation, and how it is used in greenhouses. In the control of plant growth, or photomorphogenesis, there are at least five types of information that derived from the radiation environment: radiation quantity, radiation quality, direction of radiation, duration of radiation (timing of light-dark transitions), and polarization. The radiant energy used by plants comprises a small part of the total electromagnetic spectrum. Instruments for measuring radiation separated in to three classes: radiometers, photometers, and quantum meters. Instruments made to measure radiation are manufactured to follow the cosine law as closely as possible. A few examples are provided in Glass-covered radiometers, such as the Eppley or Kipp-Zonen, convert radiant energy to heat. For greenhouse practices, the three most important factors concerning solar radiation are: the total energy that may be available, the length of the light and dark hours, and the quanta in the various wavebands, influencing photosynthesis and photomorphogenesis.
