I note that Blue LED's are out because they are very costly. Problem is according to the summary published by NASA in conjunction with several universities is Blue is essential to plant growth. Recommendation from that study is from 1% to 20% blue LED depending on plant and growth requirements.
Offered by John.
Please note that NASA used blue fluorescent lights as the supplementary blue light source. This is why I recommend the use of luminous tubes (neon lights). The luminous tube is the only routinely rebuildable light source I am aware of, and is long lasting at that (5 to 10 years). True a certain web of technologies must be maintained to support luminous tubes and you must be willing to deal with a modest amount of toxic mercury. I know of no other alternative for blue light. The luminous tube will also be able to supply needed ultraviolet light for disinfecting and vitamin D production.
Offered by Steve