Narrowband photosynthetically active radiation ('PAR") substantially only at each of multiple emission wavelengths yields good photosynthesis at reduced energy cost
Produced PAR neither replicates the spectral ban—width of sunlight at the surface of the earth, nor the absorption spectrum of green plants, nor the absorption spectrum of photosynthetic processes, but—based on discovery that PAR at only a number of unique wavelengths is optimally energy-efficient to promote normal or better plant growth—instead desirably concentrates PAR emissions in a limited number, preferably about nine (9), narrow bands. Narrowband, even extremely narrowband, radiation is preferred at 430 and 662 nanometers wavelength； 453 and 642 nanometers wavelength and still other wavelengths. Preferably more than 50% of the total PAR flux is within a total bandwidth of less than 160 nanometers wavelength in the range between 360 and 760 nanometers wavelength, and more preferably 90% of the PAR flux is within a total bandwidth of less than 80 nanometers wavelength within this range.
