Higher yields and shorter production times justify cost. When all factors are optimized . . . Plants are exposed to 300 fc on cloudy days to up to 12,000 fc on bright sunny day. Many plants become light-saturated at 3000 fc. African violets burn above 1000 fc.
Thought is that it is heat generation by exposure to energy of light.
Plants vary in their response to various wavelengths. In general, blue and red most effective. Less overhead equipment. Commercial glass cleaning products. Plant spacing improves light penetration and lower leaf exposures to light.