For those interested, the reasoning behind using only red and blue light is well described in the review article below- Carvallo et al. 2011. Light requirements in microalgal photobioreactors: an overview of biophotonic aspects. Appl Microbiol Biotechnol, 89: 1275 - 1288. The authors specifically talk about LEDs too (pg 8-10). The narrow band width emitted by LED lights permits light to be focused in wave lengths best absorbed by chlorophyll a. Here is my short summary of important facts in Carvallo et al. 2011. Chlorophyll a absorbs light primarily between 450 - 475 (blue) and 630-675 nm (red). Chlorophylls excited by a "blue" photon get "too" excited and need to shed energy as heat/fluorescence before it can begin the photochemical process (electron transport chain and Calvin cycle). Chlorophylls excited by a "red" photon are energized to the ideal level, and can proceed directly to the photochemical process. Even though some energy from blue light is wasted, microalgae growth rates are still increased with low levels of blue light. Microalgae are often grown with "only" 5-10% blue light (I put only because that is very little to us reefers!).