Reference

Here is where we are posting all the academic studies/reviews that we 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 we will continuously add to it over time, so if you find something that we should have mentioned, then do please send ​us the study for ​us to check out.

General

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.[57]

  • 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

  • lettuce.
  • 24% green light (500-600nm) enhances growth.
  • more than 50% green light inhibits growth.

Far-red Light (710-800nm)

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.