Ambient lighting: the general lighting present in an area, excluding task lighting and accent lighting, but including daylight.

Ballast: a device used with an electric-discharge lamp to obtain the necessary circuit conditions for starting and operating. All fluorescent lights require a ballast for correct operation. Many light manufacturers are using energy-efficient T-8 ballasts instead of traditional T-12 ballasts.

Candela: a unit of luminous intensity (strength) from a light source or lighting system.

Cold cathode: a type of lamp that provides a high lumens output with lower energy costs and far less maintenance costs than fluorescent lighting systems. It is not affected by on-off cycles.

Direct lighting: lighting by luminaries distributing 90 percent to 100 percent of the emitted light in the general direction of the surface to be illuminated. It usually refers to light emitted in a downward direction.

Disability glare: glare that results in reduced visual performance and visibility. It is often accompanied by discomfort.

Discomfort glare: glare that produces discomfort. It does not necessarily interfere with visual performance or visibility.

Efficacy: a measurement of how effective a light source is in converting electrical energy to lumens of visible light.

Energy Star: a program administered by the U.S. Environmental Protection Agency (EPA) and the U.S. Department of Energy. It encourages homes, hospitals, offices, retailers, schools and manufacturing plants to install energy-efficient lighting.

Eye sensitivity: a curve depicting the sensitivity of the human eye as a function of wavelength or color. The peak of human eye sensitivity is in the yellow-green region of the spectrum.

Fluorescent lamp: a high-efficiency lamp that uses an electric discharge through inert gas and low-pressure mercury vapor to produce ultraviolet (UV) energy. The UV excites phosphor materials applied as a thin layer on the inside of a glass tube. The phosphors transform the UV to visible light.

Footcandle: a unit of illuminance equal to 1 lumen per square foot.

Glare: excessive brightness caused by either direct or indirect viewing of a light source that may annoy, distract or reduce visibility.

Halogen lamp: an incandescent lamp with a filament that is surrounded by halogen gases, such as iodine or bromine, that allows it to be operated at higher temperatures and higher efficacies.

Illuminance: the quantity of light at one point on a surface.

Light-emitting diode (LED): a rugged, cool-burning, long-lasting light source. LEDs are made of semiconductor chips and emit light when a current passes through them.

Light pipe: a modular device capable of transporting and controlling the distribution of light. It provides uniform illumination over various lengths.

Lumen: a unit of measurement of the total light output from a specific source.

Luminaire: a complete lighting unit, consisting of a lamp and ballast, together with parts designed to distribute the light, protect the lamp and connect them to the power supply. Also referred to as a “fixture.”

Luminance: a measure of surface brightness when an observer is looking in the direction of the surface. It is measured in candelas per square meter.

Lux: a unit of illuminance or light falling onto a surface. One lux is equal to 1 lumen per square meter. Ten lux equals approximately 1 footcandle.

Mercury lamp: a high-intensity discharge light source that operates at a relatively high pressure and temperature. Most of the light is produced by radiation from excited mercury vapor.

Reflection: the process by which flux leaves a surface or medium from the incident side.

Reflector: a device used to redirect light by the process of reflection.

Refraction: the process by which the direction of a ray of light changes as it passes obliquely from one medium to another.

Solid-state lighting: energy-efficient lighting applications that use LEDs.

T-8/T-12: refers to a measurement system that designates the diameter of a tubular bulb in eighths-of-an-inch increments. For instance, a T-8 bulb measures 1 inch in diameter.

Task lighting: supplemental lighting provided to assist in performing a localized task, such as assembling electrical components.

Visual task: details and objects that must be seen to perform an activity, such as assembling a medical device.