Workplace illumination is a normal requirement for greenhouses, and flower growers need to be aware that low light intensities of light can modify plant development (e.g. flowering, dormancy). The use of supplemental lighting is an issue with respect to “light pollution”. Supplemental lighting-LED grow light is used for several purposes within greenhouse systems:
• LED grow lights are turned on before dawn and/or in the evening in order to extend the photoperiod and achieve developmental control (conversely, blackout curtains are used during daylight hours to shorten the photoperiod). Less commonly, the equivalent to daytime extension can be achieved by providing a crop with one or two hours of illumination during the middle of the night (night interruption lighting). The intensity requirement for photoperiodic regulation of plant development is low. A traditional procedure is to use 100W incandescent lamps suspended 3 feet above a crop on 4.5 foot centers. High intensity discharge lamps, more widely spaced, are also used for this purpose.
• Low intensity supplemental light can sometimes benefit low-light requiring plants. (e.g. a little supplemental light like 14w led grow light, 15w led grow light, 50w led grow light, 90w ufo led grow light can improve results with African violets)
• High intensity lighting like 120w led grow light, 300w led grow light, 600w led grow light, sufficient to significantly increase photosynthesis, is expensive in terms of capital and operating costs. High intensity treatments during the main phase of growth are only used with high-value crops (e.g. roses). It is used during the early establishment of greenhouse vegetable crops and some flower crops. Furthermore, it is sometimes used during both asexual and sexual plant propagation.