Generally, only a low intensity of blue is needed in a light spectrum for fully functional photosynthesis. Therefore, indoor lighting (such as in vertical farming) and greenhouse lighting usually include blue in the spectrum.
Generally, blue light suppresses extension growth; plants grown with blue light are usually shorter and have smaller, thicker and darker green leaves compared to plants grown without blue light (Figure 1). In the production of ornamentals, these attributes can be desirable because in essence, blue light can act as a growth regulator. The utility of blue light as a growth regulator is pronounced with indoor lighting and generally has less or no growth-inhibiting effects in supplemental greenhouse lighting. There are some reports in which extension growth is actually promoted under only blue light, although this response seems to be crop specific.
