Here is where I am posting all the academic studies/reviews that I have come across that will allow us to build towards an ideal model for using LED grow lights. It is by no means all inclusive and I will continuously add to it over time, so if you find something that I should have mentioned, then do please send me the study for me to check out.
Okamoto et al. Acta Hort. (ISHS), vol. 440, pp. 111-116, 1996.
- An early study proving the need for blue light as well as red light.
- They were able to grow lettuce using 33% blue LEDs ; 67% red LEDs.
Yorio et al. HORTSCIENCE 36(2):380–383. 2001.
- Lettuce, radishes & spinach.
- equivalent PAR.
- grow better under cool-white fluorescent vs Red LEDs (660nm) + 10% blue fluorescent lamps (400-500nm).
Green & Yellow Light (500-600nm)
Folta & Maruhnich. Journal of Experimental Botany, Vol. 58, No. 12, pp. 3099–3111, 2007
- General review concluding that green / yellow light (500-600nm) generally negates the growth effects of blue / red light.
Dougher, T. A. O. and Bugbee, B. Photochemistry and Photobiology, 73: 208–212, 2001
- demonstrated that yellow light was suppressing lettuce growth
Kim et al. Acta Hort. 711:111–119. 2006
- 24% green light (500-600nm) enhances growth.
- more than 50% green light inhibits growth.
Rajni Govindjee, R., & Rabinowitch, E. Biophysical Journal, 1, pp 377-388, 1961
- indicated that plants grow better with Far-red light and red light in combination than with red light alone (known as the ‘Emerson Enhancement Effect”).
Franklin, K. New Phytologist, 179: 930–944, 2008.
- Review of the importance of the Red:Far-red (R:Fr) ratio in determining how plants grow.
- low R:Fr ratio can cause plants to activate shade avoidance mechanisms and flowering.
- low R:Fr ratio can also have undesirable effects on plants such as stem elongation, leaf hyponasty (leaves pointing skyward), and reduction in biomass.