Starting a decade ago, researchers focused on the potential of LED (light-emitting diode) lighting for greenhouse horticultural crops, whether ornamental or vegetable. Usually, high pressure sodium lamps (HPS) are the most used in the greenhouse industry around the world. Their efficiency for converting electrical energy into radiant energy (or photosynthetically active radiation, PAR (400 to 700 nm)) is between 26 to 30 per cent. Depending on the lamp model, HPS lamps have between seven and 10 per cent emission in the blue wavelengths (400 to 495 nm) The emission spectrum of an HPS lamp cannot be modified to suit the more specific needs of cropspecies and those of the market. Among all plant-specific wavelengths, blue wavelengths are known to favour photosynthesis and development of anthocyanins, which are responsible for the purple colouration found in plants. In contrast to HPS, LEDs allow such a customization of the spectrum, i.e. selecting only pure blue (wavelengths 450 to 495 nm). Hence, their use in greenhouses would enhance purple pigmentation of purple ornamental grass.
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