Here's why people want less blue:
Although wheat, and possibly all grasses, appears to have minimal sensitivity to spectral quality (Dougher and Bugbee, 2001); tomatoes are exquisitely sensitive; cucumbers, radishes and peppers have intermediate sensitivity; soybeans and lettuce have low sensitivity (Snowden et al., 2016).
(Bugbee 2016,
Toward an optimal spectral quality for plant growth and development: the importance of radiation capture)
Recent studies have examined a range of BL fractions and
found highest dry mass for lettuce, radish and pepper between about 5 and 15% BL. Cope
and Bugbee [10] and Cope et al. [11] found that dry mass and leaf area decreased above 15%
BL for lettuce, radish and pepper. Hernández and Kubota [12] reported decreased dry mass
and leaf area for cucumber when the BL fraction increased above 10% with a pure RL background. In a greenhouse study, Hernández and Kubota [13] found that dry mass and leaf
area of cucumber decreased with increasing BL. Wang et al. [14] found that lettuce shoot
dry mass steadily decreased as BL increased from 8 to 50%. Dougher and Bugbee [15]
described histological effects of BL on development of lettuce and soybean and found that
increased BL decreased cell expansion and division in the stems and leaves of soybean. Interestingly, Son and Oh [16] reported the highest fresh and dry mass of lettuce at 0% BL (pure
red light), but the plants were chlorotic and etiolated.
Among the broad spectrum treatments at the higher PPF, increasing BL in four increments from 11 to 28% reduced
dry mass in tomato, cucumber, and pepper by 22, 26, and 14% respectively, but there was no
statistically significant effect on radish, soybean, lettuce and wheat. At the lower PPF, dry mass
was reduced by 41% in tomato, but the effects of BL on the other species were less than 6% and
were not statistically significant
(Snowden 2016,
Sensitivity of Seven Diverse Species to Blue and Green Light: Interactions with Photon Flux)
Good reads
Not saying I'm 100% on board, blue light surely brings about other differences. But the dry weight numbers don't lie.
