Why measure light
As the driving force for photosynthesis, light is fundamentally important for crop production. Plant growth and development is significantly influenced by both the quantity and the quality of light.
How is light perceived
Lux meters measure light similar to how the human eye perceives brightness: strongest in the 500-600 nm range. For plants, however, the light that can be used for photosynthesis (PAR / Quantum Light) is in the spectral range from 400 to 700 nm. At that different wavelengths help plants achieve different goals as well.
How light impacts plant development
Ultraviolet Light (380-410 nm): can support mineral metabolism and formation of vitamin D in plants; also useful for killing insects.
Blue light (wavelength 440 - 460 nm): stimulates the plant growth on stems and leaves; helps to avoid excessive growth.
Red Light (630-660 nm): stimulates the root growth, chlorophyll biosynthesis and carbohydrate accumulation; provides better germination, blooming and fruiting.
Infrared Light (730 nm): speeds up the phytochrome conversion which reduces the time a plant takes to go into a night time state. This allows the plant to produce a greater yield