What device is used to direct, control, or modify light?

A luminaire is designed specifically to direct, control, or modify light output. This device refers to a complete lighting unit that encompasses not just the light source, but also the housing and any optical elements used to manage the distribution of light. Luminaires are essential in various settings, such as in buildings, streets, and outdoor spaces, enabling efficient and effective illumination while also considering aesthetic factors.

Other terms mentioned serve different functions. A ballast, for instance, is used with certain types of light sources, particularly fluorescent and HID lamps, to provide the necessary starting voltage and regulate the current to ensure proper operation. Candlepower is a unit of measurement for luminous intensity, describing how much light is emitted in a particular direction. Lumen measures the total quantity of visible light emitted by a source. While these terms are related to light, they do not fulfill the role of directing or modifying light in the way a luminaire does.