Grow Lights used in Hydroponics
A very important part of Controlled Environment Agriculture (CEA), as developed by Dr. Louis Albright of Cornell University, is the illumination provided by the grow lights. Even though in the summer months and during good weather sunlight provides the lumens necessary for photosynthesis, on cloudy or rainy days and during the dark days of winter, it is necessary to supplement the natural light in the greenhouses with artificial grow lights. Fruits and vegetables are just as happy to grow under grow lights as they are under sunlight.
For many decades, artificial grow lights were mainly of the High Intensity Discharge (HID) variety. The two main subgroups in this category are Metal Halide (MH) grow lights, which produce illumination in the blue end of the spectrum, close to natural sunlight, and High Pressure Sodium (HPS) grow lights, which provide light on the red end of the spectrum. An abundance of blue light is needed by plants during their vegetative growth, while the red spectrum light is needed more during the bloom phase. Vegetables such as lettuce which are harvested before they go into their bloom stage (if you allow lettuce to bolt or go to seed it acquires a bitter taste) need only the blue spectrum light from start to finish.
CEA, as perfected by Dr. Albright, involves having light sensitive sensors located throughout the Nutrient Pond surface as well as at the level of the plant canopy which measure the exact amount of lumens reaching each section of the crop.
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