What is light?
Light can be described as electromagnetic energy or waves moving from one point to another. Each wave for a certain wavelength looks the same; it has the same beginning and ending, and the same height and width. Some wavelengths are shorter, meaning faster wave formation, while other wavelengths are longer (slower wave formation).
The whole range of light wavelengths is called the light spectrum. Wavelengths are measured in nanometers (nm), which is equal to one thousand millionths of a meter (10^9). For example, ultraviolet light lies between 100 and 400 nanometers, while red light can be measured around 680 nanometers.
That particular band of light that growers are especially interested in is PAR or Photosynthetically Active Radiation. PAR light lies between the range of 400 and 700 nanometers and is also called “visible light”. Plants use PAR light for photosynthesis or growth.