High intensity discharge bulbs and fluorescent bulbs have a viewing angle of 360°, but LED grow lights typically have a 120° viewing angle. Full spectrum LED lights can come with 2 settings, a red setting and a blue setting. The blue setting will support vegetative growth in cannabis, and the red setting will support flowering.
Full spectrum LED provides 730 nm (IR), 660 nm, 630 nm, 610 nm, 580 nm, 460 nm, 430 nm, and 410 nm (UV) light wavelengths. Growers usually need LED grow lights for cannabis that have 32 watts per square foot of space, or about 32 watts per plant. Incandescent bulbs are very familiar light bulbs that are used in homes. Halogen lamps are a type of incandescent bulb that has a small amount of a halogen gas such as iodine or bromine inside the bulb. Halogen lamps are more efficient than a standard incandescent bulb, but are less efficient than HID bulbs. Halogen lamps can be used for horticulture, but are very inefficient at generating light that supports plant growth. The spectral output of many halogen bulb is in the orange to yellow range. Cannabis plants grown under halogen lamps tend to have long internode spacings, poor vegetative growth, and low yields. For these reasons, cannabis growers do not commonly rely on halogen lamps to provide photosynthetic lighting.
Halogen lamps also produce a dangerous amount of heat that presents a major fire hazard. High pressure sodium (HPS) lamps and metal-halide (MH) lamps are two popular types of high intensity discharge (HID) lamps used in growing cannabis. HPS lamp wavelength spikes at 632 nm, 605 nm, 589 nm, and 568 nm light wavelengths. MH lamp wavelength spikes at 674 nm, 630 nm, 583 nm, 564 nm, 540 nm, 497 nm, and 422 nm. Cannabis plants respond better to HPS lamps, or a combination of HPS and MH lamps than to MH lamps alone. HID lamps produce a lot of heat, so it is important to have very good ventilation when they are used. HID lamps should have about two feet of space above the crop canopy to avoid burning the plants. High pressure sodium (HPS) lamps use sodium in an excited state to produce light. HPD grow lights are a high efficiency bulb that is preferred for flowering due to large amount of red light. HPS lamps have unbalanced full spectrum light with large outputs of green, yellow, and red light and very little violet, blue, and cyan light. HPS bulbs replace MH bulbs after vegetative growth. Small-scale growers can have success with 150W, 250W, and 400W HPS grow lamps for cannabis. Commercial growers producing large crops usually prefer 600W or 1000W HPS grow lams for cannabis. Metal halide (MH) lamps are a type of HID lamp that produces light by running an arc current through vaporized mercury and metal halide gas. Efficacy of MH lamps range from 75-105 LPW (lumens per watt). Metal halide grow lamps require a minimum of 4-15 minutes to restart after turn-off, this is known a a restrike period. Metal halide grow lamps are popular for use in vegetative growth phase of cannabis due to very high blue content of light. Common wattages of metal halide grow lights fro cannabis include 250W, 400W, 600W, and 1,000W. Ceramic metal halide (CMH) lamps are a new variant of metal halide grow lamps that use an extremely hot ceramic tube to ionize gasses and salts chosen for a specific spectral output. CMH are becoming popular with indoor cannabis growers because they produce light that is very similar to natural sunlight. CMH grow lamps also have more red than a standard metal halide lamp, so they deliver more light that can fuel photosynthesis. Mercury vapor lamps produce light by arcing electricity through mercury vapor. They are very old members of the HID family that have very low efficacy and do not have the proper color spectrum for plant growth. HID lamps receive electrical currents through a ballast that makes sure they run on the appropriate voltage from an outlet. The total wattage needed by the ballast and lamp are the input watts.
Hoods often integrated with the ballast for HID lamps, some hoods have a reflective lining to help redirect light towards the plants.
Reflective hoods are called reflectors or parabolic reflectors.