Glossary of Commercial Lighting Terms L-Z

Lamp - The term used to refer to the complete light source package including the inner parts as well as the outer bulb or tube. "Lamp", of course, is also commonly used to refer to a type of small fixture such as a table lamp.
Lamp Watts - Input power used to operate lamps.
LED - Light Emitting Diode.  LED Lamps consume very little energy, produce very little heat and have average lamp life of up to 50,000 hours.

Light - The energy that allows us to see. Light can be expressed in terms of intensity (candela), flux (lumen), luminance (candela/square foot), and exitance (lumen/square foot).

Light Loss Factor (LLF) - A factor used in calculating illuminance after a given period of time and under given conditions. It takes into account temperature and voltage variations, dirt accumulation of luminaire, lamp depreciation, maintenance procedures and atmospheric conditions.

Light Pollution - The scattering of electric light onto the atmosphere, usually caused by luminous flux above the horizontal. Light pollution is often referred to as sky glow or sky brightness.

Light Trespass - Any lighting that strays from its intended purpose, causing visual annoyance. A severe form of light trespass involves glare.

Lighting Power Budget - Lighting power budget is the upper limit of power to be available to provide the lighting needs for a building, including all permanently connected lighting.

Lighting Power Density - Lighting power density is the maximum allowable lighting density permitted by the code. It is expressed in watts per square foot for a given occupancy/space type.
Low Pressure Sodium - These are also HID bulbs with a sodium gas, and produce a yellowish light. These lamps have an average life span 18,000 hours. Typical usage: Security areas (work well with security cameras) Outdoor.
Lumens Per Watt - A measurement of white light produced by each output watt.
Luminaire - A complete lighting unit consisting of a lamp (or lamps), together with the parts designed to distribute the light, position and protect lamps and connect them to the power supply.
Luminaire Component Depreciation (LCD) Factor - The multiplier to be used in illuminance or luminance calculations to relate the initial flux output of a clean luminaire to the reduced flux output due to permanent component deterioration at a particular time in the future chosen for desirable maintained values.

Luminaire Dirt Depreciation (LDD) Factor - The multiplier to be used in luminance or illuminance calculations to reduce the initial light level provided by clean, new luminaires to the reduced to the light level that they will due to dirt collection of the luminaires at the time at which it is anticipated that cleaning procedures will be instituted.

Lumen Maintenance - The lumen output provided by a light bulb at a given point or percentage of it’s life.
Lumen Efficacy - The light output of a source divided by the total power input to that source. It is expressed in lumens per watt.
Luminance - This term is used to describe the specific light which comes off the surface whether off a filament, light bulb, lens, louver, tabletop, etc. Luminance varies with both the direction at which you view the surface and its gloss characteristics. Luminance is measured in candela per square foot.

Lux (lx) - Lux is an international metric unit of luminance. One lux is equal to one lumen per square meter (lm/m2)

Maximum Overall Length (M.O.L.) - The end to end measurement of a light bulb or lamp expressed in inches or millimeters.
Mean Lumens - The average light output of a lamp over its rated life. For fluorescent and metal halide lamps, mean lumen ratings are measured at 40% of rated lamp life. For mercury, high pressure sodium, and incandescent lamps, mean lumen ratings are measured at 50% of rated lamp life.

Mercury Vapor Lamp - A high-intensity discharge light source operating at a relatively high pressure (about 1 atmosphere) and temperature in which most of the light is produced by radiation from excited mercury vapor. Phosphor coatings on some lamp types add additional light and improve color rendering.  Mercury vapor lamps tend to produce a bluish green light.
Metal Halide Lamp - These HID bulbs produce a blue-white type light, these bulbs are very efficient, and long lasting, average life span 20,000 hours.
Mounting Height (MH) - The vertical distance between the roadway or parking lot surface and the center of the apparent light source of the luminaire.

Nadir - The vertical projection beneath the apparent light source of a luminaire. Offset: The distance from the face of curb or edge of the traveled roadway to the traffic hazard (lighting poles, etc.).

NFPA - National Fire Prevention Agency.
Neodymium - A rare earth element used in glass that filters out the excessive yellow spectrum to which our eyes are most sensitive.

Ohm - The unit of measurement of electrical resistance. It is that resistance through which a difference of potential, or electromotive force, of one volt will produce a current of one ampere.

Ohm’s Law - Volts X Amps = Watts

Parabolic Aluminized Reflector (PAR) Lamp - A type of incandescent lamp made of a heavy glass that controls its light beam using a reflector and lens. Par lamps are generally waterproof.
Photo Control (Photocell) - A device used to detect light levels, which controls the electrical operation of a light fixture when changes occur.
Preheat Lamp - A fluorescent lamp in which the filament must be heated by use of a starter before the arc is created. These lamps are typically operated with electromagnetic ballasts.
Programmed Rapid Start - A lamp starting method which preheats the lamp filaments, while not allowing the lamp to ignite, and then applies the open circuit voltage (OCV) to start the lamp. The user may experience a half to one second delay after turning on the lamps while the preheating takes place. This type of starting circuit keeps lamp end blackening to a minimum and improves lamp life performance, especially in applications where the lamps are frequently switched on and off.

Pulse Start Lamp - A specially designed metal halide lamp that uses ballast with igniter for starting.

Rapid Start Ballast - This is a type of fluorescent ballast that applies a low filament voltage to preheat the cathodes. Simultaneously, a starting voltage (lower than that used in instant start ballasts) is also applied to strike the arc. When the cathodes are hot enough the lamp will strike.
Rapid Start Lamp - A fluorescent lamp with two pins at each end connected to the filament. The filaments are heated by the ballast to aid in starting. Some rapid start lamps may be instant started without filament heat.
Rated Life - See Average Rated Life
Reflector Lamp - An incandescent, compact fluorescent or HID lamp with a built-in reflecting surface. Incandescent and HID versions are made from a single piece of blow-molded soft or hard glass. CFL versions may be one piece or may be designed so that the inner lamp can be replaced.
Restart or Re-Strike Time - The amount of time from return of power after an interruption to the point of lamp ignition.
Re-Strike - To re-ignite the arc of a HID lamp.
Retrofit - A self-ballasted replacement lamp that converts a light source to either change its characteristics or reduce energy consumption.

Setback - The lateral offset of the pole from face of curb or edge of traveled roadway.

Shroud - A glass cylinder that surrounds the arc tube in open fixture rated metal halide lamps. The shroud is designed to contain hot arc tube particles and glass bulb breakage, should a rupture occur. This protection reduces the risk of using metal halide lamps in open fixtures.
Starting Temperature - Refers to the lowest outside temperature a fluorescent tube will operate at. This temperature may be determined by the ballast or specific qualities of the lamp in question.
Street Side - The horizontal direction that is toward the roadway from the nadir of the luminaire.

Surge Arrester - A device which protects lines and equipment against voltage surges caused by lightning or abnormal system conditions which can damage cable or equipment insulation. The surge arrester is connected from the line to ground to provide a conducting path. This limits the voltage on lines or equipment and dissipates excess energy harmlessly.

Transformer - An electromagnetic device for changing the voltage level of alternating-current electricity.

Troffer - An inverted, usually metal, light fixture suspended from a ceiling as a fixture for fluorescent lighting tubes.
Two-Pin Compact Fluorescent Lamps - Type of lamps that have the glow bottle starter built into the base of the lamp. Traditionally, 2-pin lamps are designed to work with electromagnetic ballasts.

UL (Underwriters' Laboratories, Inc.) - Laboratory that sets safety standards for building materials, electrical appliances, and other products.