Lighting term glossary. Hope this helps!

Ambient Light Lighting throughout a space that produces general illumination.

Ampere (amp) Unit to express the flow quantity of electricity. Analogous to gallons per minute.

Baffle An accessory that prevents light from producing glare at certain angles.

Ballast Auxiliary unit used with HID lamps to provide the power to start the lamp and regulate the voltage, current & waveform while it is in use. A ballast is required for each HID lamp.

Brightness A negative term associated with glare producing luminaries.

Bulb Layman’s term for “lamp”.

Candela The basic unit of measurement of luminous intensity from a light source in a specific direction.

Circuit Breaker A switching device that can be manually operated that automatically opens (switches off) when more than the rated current passes through. Generally rated in amps. A typical residential circuit breaker is 15 or 20 amps.

Color Temperature An expression of light source color or whiteness, stated in degrees Kelvin. Warmer (more yellow) light has a lower color temperature and cooler light (more blue) has a higher color temperature.

Conductor A metallic material that has low resistance to electrical flow such as copper. A circuit must have at least 2 conductors.

Efficacy (efficiency) A measurement of how many lumens a lamp produces per watt consumed.

Fixture Layman’s term for “luminaire”.

Floodlighting Indiscriminate lighting of an area usually associated with security or utility functions.

Footcandle (fc) A unit of measurement of luminescence. For reference: an office desktop typically has 50-75 fc of light falling on it if lit from overhead fluorescent lamps. A primary focal point tree in a residential garden should have about 5 fc average on it

Fluorescent A low-pressure lamp that has a phosphor coating that transforms ultraviolet energy into light. Although efficient they are physically very large.

FX Term to describe Lighting Effects – generally used in theatrical applications. Also the manufacturer of some great lighting components.

Gauge A measurement of electrical conductor (wire or cable) size. The lower the number, the thicker the cable. 8-gauge cable is twice the size of 12-gauge.

Glare A negative term describing uncontrolled light that produces discomfort to the viewer.

Ground A non-current carrying metallic connection to earth. All 120v circuits must be grounded – 12v circuits do not. The green wire on a 120v circuit is typically the ground.

Ground Fault Interrupter (GFI) A device that detects abnormal current patterns and shuts off power. GFI’s are always required on outdoor circuits.

Halogen See Tungsten-Halogen Lamp.

Hard Light Light that produces very high contrast such as the grazing effect

High Intensity Discharge (HID) A lamp that produces light when electricity excites different gases within a pressurized glass envelope. HID lamps include mercury vapor, metal halide and high-pressure sodium types. See also Ballasts.

High Pressure Sodium Lamp An HID lamp that produces light from sodium vapor, producing a distinctly yellowish color. Used widely as streetlights.

Hot The conductor or surface that has voltage present. A hot and a common or neutral creates an electrical circuit.

Illuminance The amount of light striking a surface or object, measured in footcandles or lumens.

Incandescent Lamp A lamp that produces light when electricity heats a tungsten metal filament.

Lamp Technical term for “bulb”.

Line Voltage Generally means 120 volts.

Low Pressure Sodium Lamp An HID lamp that produces light from sodium vapor, producing a distinctly pinkish color. Used for streetlights and security.

Low-voltage Lighting A general term given to a system that is powered by a step-down transformer that reduces a 120v power input to a 12v output.

Lumen The unit of measurement for the amount of light emitted by a lamp. One lumen per square foot is one footcandle.

Luminaire Technical term for “fixture”. A complete lighting unit consisting of a lamp holder, lens and adjustable components.

Mercury Vapor Lamp An HID lamp that produces light by radiation from mercury vapor. Mercury lamps have a distinct blue-green color and are a popular moonlight source for very large trees in commercial environments. Some folks think this type of lamp makes everything look ghoulish.

Metal Halide Lamps An HID lamp that produces light by radiation from metallic vapors. This type of HID lamp has the most neutral color rendering effect so it is appropriate for very large-scale color sensitive uplighting.

Neutral A conductor that is common to other circuits and carries no current.

Ohm A measurement of electrical resistance that causes voltage loss in circuits. Also, the name of the dead dude that invented electricity.

PAR Lamp Parabolic aluminized reflector lamp or sealed beam lamp. Generally used for auto signal or headlights.

Quality of Lighting A description of the aesthetic appearance of an illuminated environment indicating the use and control of light sources.

Reflectance A measure of the amount of light that strikes a surface that is reflected. Light-colored smooth surfaces have a high reflectance.

Resistance Measured in ohms – analogous to friction in hydraulics. A measurement of the restriction of the free flow of electrons in electrical conductors. Copper has a low resistance making it a good conductor – Glass has a high resistance making it a good insulator.

Short Circuit An unwanted flow of current between two conductors causing the circuit breaker to trip.

Shield An opaque unit that shields a light source from direct view at certain angles. See also Glare

Task Lighting The function of providing illumination for specific purposes such as recreation or utility.

Transformer An electrical device used to step down 120-volt current to 12-volt current for use on low-voltage lighting systems. A transformer provides roughly 1/10th of the input power.

Tungsten-Halogen Lamp A type of incandescent lamp containing a tungsten filament within a pressurized quartz envelope, which is filled with halogen gas. Also referred to as a quartz or halogen lamp. The halogen gas recycles the burned off tungsten particles back onto the filament thereby dramatically extending the lamp life. Generally smaller and more energy efficient than 120v incandescent lamps.

Volt (V) Unit to describe the electrical force that causes current to flow – analogous to PSI in hydraulics.

Volt-Ampere (VA) A measurement of consumption. Volts x Amps = Watts. Most transformers’ wattage ratings are expressed in VA.

Watt (W) Unit of electrical consumption. See Volt-Ampere. Don’t confuse wattage with light output – light is expressed in lumens or footcandles. Ex: heat lamps consume a lot of wattage but produce little light.