Glossary - H

H 

hard light that causes an object to cast a sharply defined shadow. 

hazardous location an area where ignitable vapors or dust can cause a fire or explosion created by energy emitted from lighting or other electrical equipment or by electrostatic generation. 

heavy-duty floodlight (HD) a weatherproof unit having a substantially constructed metal housing into which is placed a separate and removable reflector. A weatherproof hinged door with cover glass encloses the assembly but provides an unobstructed light opening at least equal to the effective diameter of the reflector. 

high-intensity discharge (HID) lamp an electric-discharge lamp in which the light-producing arc is stabilized by bulb wall temperature, and the arc tube has a bulb wall loading in excess of 3 W/cm2. HID lamps include groups of lamps known as mercury, metal halide, and high-pressure sodium. 

high-key lighting a type of lighting that, applied to a scene, results in a picture having gradations from middle gray to white with comparatively limited areas of dark gray and black. Also, intense, overall illumination. In motion pictures, high-level accent lighting with strong contrast (dark deep shadows with little or no middle gray). See low-key lighting. 

high-mast lighting illumination of a large area by means of a group of luminaires that are designed to be mounted in fixed orientation at the top of a high mast, generally 20 m (65 ft) or higher. 

high-pressure sodium (HPS) lamp a high-intensity discharge (HID) lamp in which light is produced by radiation from sodium vapor operating at a partial pressure of about 1.33 × 104 Pa (100 Torr). Includes clear and diffuse-coated lamps. 

hue of a perceived color the attribute that determines whether it is red, yellow, green, blue, or the like.

hue of a perceived light-source color† the attribute that determines whether the color is red, yellow, green, blue, or the like. See hue of a perceived color. 

hydrargyrum medium-arc-length iodide (HMI) lamp an arc light source utilizing mercury vapor and metal halide additives to produce illumination in the 5000 to 6000 K range. Requires a ballast and ignitor system for operation.