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Heins, 2006). Although INC lamps are effective, they are inefficient at converting electrical energy into light (Narendran, 2011); approximately 14% of the total radiation output emitted from a 60-W INC lamp is between 400 and 850 nm (Thimijan and Heins, 1983). Many governments around the world have passed laws to reduce electricity consumption by phasing out INC bulbs and replacing them with energy-efficient alternatives, such as compact fluorescent (FL) lamps and light-emitting diodes (LEDs) (Narendran, 2011). HPS lamps provide light with considerably greater photosynthetic photon efficiency, ranging from 0.9 to 1.7 μmol∙J–1 (Nelson and Bugbee, 2014); however, a large amount of shortwave radiation is also emitted by the HPS lamps. This energy can increase plant canopy temperature when delivered at a high irradiance, which can be desirable in some circumstances and undesirable in others, and consequently there must be sufficient distance between the lamps and plants to prevent tissue damage. In addition, since low-intensity lighting is sufficient to regulate flowering of a wide range of plants, the high radiation output from HPS lamps is unnecessary and can be energy intensive. Some greenhouse growers also use other high-intensity electric lamps, such as metal halide and mercury vapor lamps, which use electric arcs to produce photons through metal halides and/or vaporized mercury. Metal-halide lamps have similar efficiency to HPS lamps at converting electrical energy into photons (20 to 25%) (Fisher and Donnelly, 2001). In particular, ceramic metal-halide lamps have a photosynthetic photon efficiency of 1.3 to 1.5 μmol∙J–1 (Nelson and Bugbee, 2014). Metal-halide lamps emit a higher proportion of blue (B; 400 to 500 nm) than R light than HPS lamps (Fisher and Donnelly, 2001). Light-emitting diodes An LED is a solid-state semiconductor device that permits current to move in one direction and converts electrical energy into light. Various materials are blended in an LED to 6PDF Image | LED REGULATE FLOWERING OF PHOTOPERIODIC ORNAMENTAL CROPS
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