Light-emitting diodes (LEDs) have been
proposed as a photosynthetic radiation source
for space flight growing systems and as a
more efficient source for terrestrial controlled-environment
agriculture facilities (Bula
et al., 1991). We have observed that lettuce
and other dicotyledonous plants develop excessive
hypocotyl elongation when grown
under high-intensity red-emitting LEDs as the
sole source of irradiance.
Radiant energy in the blue portion of the
visible spectrum suppresses hypocotyl and