Appendices 7.
Glossary and Symbols 7.1.
Ambient lighting: Lighting throughout an area that produces general illumination. Ballast: A device used with a fluorescent or high intensity discharge (HID) lamp to obtain the necessary circuit conditions for starting and operating. Coefficient of utilization (CU): The ratio of luminous flux (lumens) from a luminaire calculated as received on the workplane to the luminous flux emitted by lamps. When used with skylights, the coefficient of utilization is the ratio of the luminous flux from skylights received on the workplane to the daylight entering the room from the bottom of the light wells. Daylight saturation: The condition where the interior daylight illuminance level equals or exceeds the specified design illuminance level and the lighting control system thus provides maximum lighting energy savings. At saturation, any further increase in daylight illuminance will not produce additional lighting energy savings. Diffuse (Lambertian) surface: A surface that emits or reflects light in all directions and has a constant luminance regardless of viewing direction. See also specular reflecting surface. Effective aperture (EA): A measure of the light-transmitting ability of a fenestration system. Effective aperture is the product of the skylight-to-floor ratio (SFR), the visible transmittance (Tvis) and the well factor (WF). EA values range from 0 to 1.0 and are typically less than 0.1 for most practical skylight systems. Fenestration: Any opening or arrangement of openings for the admission of daylight, including any devices in the immediate proximity of the opening that affect distribution. Fixture: The housing for a light source, usually providing attachment to the building, housing for the ballast and lamps, and connection to the power source.
appendices 7-1