|Authors: ||K.-J. Bergstrand, H. Asp, H.K. Schüssler|
|Keywords: ||artificial lighting, chlorophyll, chlorophyll fluorescence, light emitting diode, photosynthesis, Solanum lycopersicum|
New lighting technologies such as light emitting diodes (LEDs) are currently being introduced in greenhouse horticulture.
However, there are still knowledge gaps regarding the influence of light spectrum on plant growth and morphology.
Tomato transplants should be compact for easy handling on transplantation, but still have a well-developed first truss for fast fruit-setting after transplantation.
The quality of the supplementary light given during production of tomato transplants in greenhouses under low light conditions in winter might have great effect on plant development.
In this three-week greenhouse experiment with four different light spectra, but the same light intensity, carried out during January-February, tomato plants (Solanum lycopersicum 'Aromata') were grown in two different LED spectra (white light with a peak in either the 620 or 660 nm region), cool-white fluorescent tubes or high-pressure sodium (HPS) lamps.
Plants grown in HPS light had the highest fresh and dry weight, but longer stems and internodes.
Plants grown in cool-white fluorescent light were similar to plants grown in LED light, but lateral shoot development was more pronounced with LED light.
The air temperature in the canopy was 1.5-2.0°C higher under HPS lamps than with the other light sources, because of stronger radiant heat.
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