Light quality impacts on growth, flowering, mineral uptake and petal pigmentation of marigold
Sams, C. E., D. A. Kopsell, and R. C. Morrow.  2016.  Acta Horticulturae, Acta Horticulturae 1134:139-145 iSHS.

Abstract:
Light quality has a significant impact on growth and development and time to flower in many plant species. Recently, the percentages of blue and red in narrow-band wavelengths of light from light-emitting diodes (LEDs) have been shown to impact mineral uptake, pigment development, and the rate of growth and development of several plant species. The objective of this research was to evaluate the effects of light quality on shoot growth, flower development, mineral uptake, and pigment content of marigold (Tagetes patula “Safari Orange”). Plants were grown in 10 cm square pots in a greenhouse ebb and flood system with a complete nutrient solution. Plants received average day temperatures of 25 C and night temperatures of 16 C. The following light treatments were utilized in this study: 1) natural sunlight; 2) High pressure sodium (HPS) lighting at 100 µmols m-2 sec-1intensity above natural sunlight intensity; 3) LED lighting with blue and red wavelengths at 50% each and intensity at 100 µmols m-2 sec-1 above natural sunlight intensity; and 4) LED lighting with blue at 25% and red at 75% and intensity at 100 µmols m-2 sec-1 above natural sunlight intensity. Total shoot growth was twice as high in all supplemental light treatments compared to the natural sunlight treatment. Shoot growth was greater in the 25% blue/75% red LED treatment than in the HPS light treatment. The 50% blue/50% red LED treatment was not significantly different from the HPS light treatment. Plants in the 25% blue/ 75% red LED treatment had 15% more blooms than plants in the 50% blue/50% red LED treatment or the HPS light treatment. All supplemental light treatments produced plants with significantly more blooms than plants in the natural sunlight treatment. Plants in the LED light treatments had greater petal pigment content than plants in the natural sunlight treatment.