“The effect of colors of light on photosynthesis is greatly overrated,” he says. “What we know is more broad-spectrum [white] lights are best.”
Purple and pink lights became popular because they were the most energy-efficient colors when LEDs reached the market, says Bugbee. White lights “have steadily improved, in my opinion,” says Bugbee.
“Green light has this tremendous advantage to penetrate deeper in the canopy,” says Bugbee. “Because it goes through the leaves, it gets to the bottom leaves, and that’s very helpful.”
Although his research (“Economic Analysis of Greenhouse Lighting: Light Emitting Diodes vs. High Intensity Discharge Fixtures,” published with Jacob A. Nelson in PLOS ONE, an open-access scientific journal) is focused on plants such as tomatoes, cannabis absorbs light the same way, he says.
Broad-spectrum white light also allows the cultivator to work more easily around the plants to get a good sense of their health and progress. “They can just see the plants better and determine health better,” says Bugbee.
After 21 studies with different LEDs across 16 grow chambers, the research showed that there wasn’t much difference in light quality, and the majority of that minimal difference had to do with leaf expansion rates, he says. Light quality doesn’t directly affect photosynthesis as much as the size or shape of the leaf itself, but research continues to show light quality has a direct effect on photomorphogenesis (in other words: how light affects plant development).
White light provided about as much energy as any other LED light, though higher levels of blue light made smaller plants with thicker leaves, according to the research. The converse was also true, with lights with lower blue levels creating taller plants with thinner leaves.
“So you would want to have warmer light colors when the plant is young, because there’s less blue and the leaves expand much more quickly,” says Bugbee. “As the plants get older, you could switch to a cool light that has higher blue ratios.”
With just one light, Bugbee says he leans toward an approach centered around cool blue light, which is more efficient overall by about 10 percent.