Abstract
New light sources for horticultural applications, intended to replace HPS lamps or
fluorescent tubes, are currently being introduced in the market.
Special attention is being devoted to LED technology, which
permits optimisation of the spectral distribution of a light source. Consequently, LED lamps are generally assumed to be more efficient for
driving photosynthesis that HPS lamps, for which much of the wavelength is outs
ide the photosynthetic optimum range.
In order to investigate the efficiency of LED technology
in greenhouse applications, different types of LED lamps were compared with
conventional HPS lamps in a series of experiments with Euphorbia pulcherrima.
Cultivation took place in greenhouse conditions with natural daylight and 100 μmol m-2s-1
supplementary lighting, supplied by white LED, red/blue LED or conventional HPS
lamps (control).
Plant development and photosynthesis rate were monitored over 4 months.
Shoot elongation was highest for plants grown under HPS lamps, as was fresh
weight. Measurements of photosynthesis under the different light sources revealed a trend
for higher photosynthesis when white LEDs were used. However, when photosynthesis
was measured at different light intensities using red/blue LEDs, plants grown under HPS
lamps had the highest photosynthesis. The air temperature in the canopy was lower when
the light was supplied with LEDs than with HPS lamps, thus delaying development. We
concluded that the quality of light supplied was a significant factor for plant development
in greenhouse conditions with supplementary light. There was a lack of correlation
between measured photosynthesis and biomass production.