Grow Light Spectrum and Cannabis

The grow light spectrum for Cannabis varies when compared to other plants as growers are focused on maximizing yields, controlling levels of THC and other cannabinoid production, increasing flowering, and to maintain overall uniformity.

Aside from visible colors, Cannabis responds especially well to wavelengths just outside of the PAR range. Therefore, an added benefit of using full spectrum LEDs is the ability to use specific doses of ultra-violet wavelengths (100-400nm), and far-red wavelengths (700-850nm) outside of the PAR range.

For example, an increase in far-red (750nm-780nm) can help stimulate Cannabis stem growth and flowering – something growers want, whereas necessary blue light in minimal amounts, can prevent uneven elongation of stems and leaf shrinkage.

So, what’s the ideal grow light spectrum for Cannabis? There’s no single spectrum since varying light exposure promotes certain plant morphology during different stages of growth. The chart below explains the concept of outer-edge PAR light spectrum use.