As the driving force of photosynthesis, light is fundametally important to plants. Plant growth and development are significantly influenced by both quantity and quality of light. Light is electromagnetic waves. The wavelength is measured in nanometers. And Light is Photons, which are a quantum or individual unit. Since individual Photons possess tiny amounts of energy, Photons are measured in mols (1mol = 60,2 x 1023 Photons).

In Agriculture and Horticulture Radiation is measured in various Ranges of wave length:

Global Radiation (wave length approx. 300 to 1100 Nanometers), covers the whole spectrum of Radiation emitted by Sun. The measurement of Global Radiation is important for calculation of Et (Evapotranspiration) and solar energy applications.

PAR Radiation (Photosynthectic Active Rays with wave length approx. 400 to 700 Nanometers), covers the wave lengths, which are used predominantly by plants for Photosynthesis.

UV Radiation (wave length approx. 250 to 400 Nanometers). UV Radiation triggers stress responses, inhibition of Photosynthesis and DNA damages in plants. Measurement of UV Radiation is further used to determine the filtering capacity of Greenhouse shadings systems and covers.