Preliminary study of green LED on lettuce growth under indoor artificial light cultivation

Red and blue light-emitting diodes (LEDs) have been the typical mixtures of light spectra applied on the indoor cultivation of leafy crops in Singapore. This preliminary study, on the use of green LED in combination with blue and red LEDs, is an attempt to improve lettuce (Lactuca sativa) growth under indoor controlled environment. The first experiment involved local Chinese lettuce grown in garden compost-filled pots under 4 artificial light sources of cool-day fluorescent light, high red/blue LEDs, low red/blue LEDs and red/blue/green LEDs with photosynthetically active radiation (PAR) ranging from 26-47 mu mol m(-2) s(-1). Higher shoot fresh weights (FW) from greater PAR of approximately 50 mu mol m(-2) s(-1) tend to promote growth efficiency. Green and blue lights seem to influence a photomorphogenic response on local lettuce plant development in particular the stem and leaf. In the second experiment, multi-leaf lettuce was grown for 50 days at 18 degrees C in a deep flow hydroponic growth chamber under 2 lighting conditions (red/blue/green and red/blue) with similar spectral intensities at higher PAR levels of 85-87 mu mol m(-2) s(-1). Overall plant size and structure of multi-leaf lettuce grown without green light were greater than the compact heads of the red/blue/green plants. Effects of green light in the presence of blue and red lights on plant growth (i.e. FW gain) remained inconclusive but it had elicited stem and leaf development.