Electromagnetic radiation of approximately 740 nm wavelength. It has been shown that far-red light inhibits many physiological processes in plants, e.g. the germination of lettuce seeds. It also counteracts the effect of *red light
. For example, if an etiolated plant is exposed to short periods of red light this results in more normal growth. However if the periods of red light are followed by periods of far-red light the plant remains etiolated. It is believed that far-red light is absorbed by a pig. ment, *phytochrome
, which mediates such responses.