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The visible colours of light from shortest to longest wavelength are: violet, blue, green, yellow, orange, and red. Ultraviolet radiation has a shorter wavelength than the visible violet light. Infra-red radiation has a longer wavelength than visible red light. White light is a mixture of the colours of the visible spectrum.
200 – 280 nm UV-C ultraviolet range which is generally harmful to plants. LEDs in this spectrum are non-existent or very expensive.
280 – 315 nm Includes harmful UV-B ultraviolet light which causes plants colours to fade. UV LEDs in this range are now available and coming down in price.
315 – 380 nm Range of UV-A ultra violet light which is neither harmful nor beneficial to most plants.
380 – 400 nm Start of visible light spectrum. Process of CHLOROPHYLL absorption begins. UV protected plastics ideally block out any light below this range.
400 – 520 nm This range includes violet, blue, and green bands. Peak absorption by CHLOROPHYLL occurs, and a strong influence on PHOTOSYNTHESIS (promotes vegetative growth)
520 – 610 nm This range includes the green, yellow, and orange bands and has less absorption by pigments.
610 – 720 nm This is the red band. Large amount of absorption by CHLOROPHYLL occurs, and most significant influence on PHOTOSYNTHESIS. (promotes flowering and budding) The ratio of red (660 nm) to far red (730 nm) in sunlight is about 1.2:1
720 – 1000 nm There is little absorption by Chlorophyll here, but PHYTOCHROME uses a nice portion. Flowering and germination is influenced. Near and above the higher end of the band is the Infra-red spectrum, which can also be heat and could cause elongation or affect water absorption & transpiration.
Many of these plant pigments have dual wavelength peaks that can be activated with led light combinations:
BETA-CAROTENE 450 nm to 480-485 nm dual peak
CHLOROPHYLL A 430 nm to 662 nm dual peak
CHLOROPHYLL B 453 nm 642 nm dual peak
PHYCOERYTHRIN 590 nm single peak
PHYCOCYANIN 625 nm single peak
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