Refers to the container for luminous gases; houses the arc in a High-Intensity Discharge (HID) lamp. Growing cannabis indoors requires a light source. Typical setups will utilize high-intensity discharge (HID) bulbs such as metal halide, high-pressure sodium (HPS), or LED lamps. The lamps are driven by a power supply called a ballast or come as an integrated unit with the bulb and power supply contained in a single component.
HID bulbs can present a risk of fire as the inner arc tube operates at very high temperatures. If the arc-tube ruptures, it can break the outer bulb glass and ignite combustible materials located below such as plastic or fabric planter pots. To reduce this risk, bulbs that are designed for “open” fixtures are available. These open fixture bulbs include an arc-tube shroud to contain the hot particles should they rupture. Some lamp fixtures also have shrouds built-in for this same purpose.