A method of growing a plant or its propagule is described. The method includes: (i) powering a light source with input power to generate an incident light; (ii) illuminating, for a period of time, a growth area of the plant/propagule with the incident light having a spectral profile defined by a first (i.e., between about 400 nm and about 470 nm), a second (i.e., between about 526 nm and about 570 nm) and a third (i.e., between about 626 nm and about 700 nm) set of wavelengths; (iii) achieving, using the incident light, a dry weight that is greater than that achieved if the growth area of the plant/propagule had been illuminated by another incident light with same amount of input power for substantially same period of time, and another incident light includes the first and the third set of wavelengths, but not the second set of wavelengths.