Growing plants indoors requires bringing sunlight indoors along with the plants. Grow lights that imitate sunlight are crucial for the successful cultivation of plants that aren’t allowed access to the real thing, and grow light technology has evolved to find the ideal kind of artificial light for plant growth. Both high-intensity discharge (HID) lamps and light-emitting diodes (LED) address issues of energy efficiency and light color, two of the biggest concerns for indoor gardeners.
A LED is a solid-state electronic device that produces light by passing an electric current through a diode composed of two materials, one electron rich and the other electron deficient. The current causes the electrons to move from the electron-rich material to the electron-deficient material, and the movement of the electrons produces light, which is focused into a beam by a plastic lens that envelops the diode. The chemical composition of the materials used in the diode determine the color of the light it emits.
Metal Halide HID Technology
Metal halide lamps, also known as HID lamps, produce light by passing an electric current through mercury and halide salts contained in a glass tube. When the lamp is turned on, a current is generated by the lamp’s ballast, and that current ionizes a gas, typically argon, within a container called an arc tube. The ionization of the gas allows an electric arc to be generated between the lamp’s electrodes, and the resulting increase in heat and pressure within the lamp vaporizes the mercury and halide, which give off light as they are vaporized.
Sunlight, which most grow lights attempt to emulate, is composed of light of all colors, or wavelengths, of the visible spectrum as well as invisible infrared and ultraviolet radiation. Metal halide lamps are capable of producing light very similar in color to sunlight and are thus well suited to use in grow lights. However, plants do not require the full spectrum of light wavelengths for optimal growth, and because the color produced by LEDs can be tightly controlled, LED grow lights can be more efficient by producing only the wavelengths of light that plants can use.
Both metal halide lamps and LEDs are significantly more energy efficient than incandescent lamps. Metal halide lamps use approximately a fifth of the energy of incandescent lamps and last up to 25 times longer. LEDs are even more efficient thanks to the fact that nearly all their energy is used to generate light, with almost no heat being produced in the process; by contrast, incandescent lamps expend up to 90 percent of their energy in the production of heat. For the same reason, LEDs are more energy efficient than metal halide lamps as well.