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Artificial illumination is used in northern Europe and Canada to supplement total daily light in winter due to the significantly lower light intensity and shorter day length compared to mid-summer. In these regions, supplementary light can improve yield and product quality, allow for year-round production, and enable day-length control for flowering. Thus, apart from facilitation of day-length control, supplementary lighting systems are not a wise-choice in terms of energy-use as well as economically, in regions receiving high intensity of sun radiation.
HPS v/s LED Lamps:
The two main kinds of artificial lighting systems installed in grenhouses are: (i) conventionally used high pressure sodium (HPS) lamps, and (ii) the more recently emerging LED lamps. HPS lamps are high-intensity discharge lamps, and produce a lot of heat in addition to light. Meanwhile, LED lamps produce ‘cold’ light, decoupled from heating. Additionally, LEDs offer the possibility for both low-intensity lighting (for inter-lighting or day length control) and high-intensity lighting (for light assimilation by the crops).
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Cost : LEDs are much more expensive than HPS lamps)
Importance of light spectrum for the crop : HPS lamps have a fixed spectrum with a high component of yellow-red light, whereas LEDs offer the option to tailor the spectrum of emitted light to improve the photosynthetic effciciencyefficiency, or secondary metabolite production).
Need for inter-lighting : ‘cold’ LEDs are suitable for inter-lighting, whereas heat-emitting HPS lamps need to be placed atleast at least 1.2 m away from the crop vertically . Since they produce a lot of heat, these and are not suitable for interlighting inter-lighting in compact growing systems where light is close to the crops.
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Careful tailoring of the lighting strategy based on crop/climate requirements, accounting for the heating effects of lamps in the climate control, developing/using more energy-efficient lighting, and switching to renewable/sustainable sources for the energy input for the lighting can improve the energy-efficiency of artificially-illuminated greenhouses. . Apart from technical developments of light sources, energy savings could also be realized by adaptations of the technical layout and positioning of lights, such as combining top-lighting and inter-lighting.