A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z
Lamp
The term used to refer to the complete light source package, including the inner parts as well a the outer bulb or tube. "Lamp", of course, is also commonly used to refer to a type of small light fixture such as a table lamp.
Life
See Rated Lamp Life.
Light
Radiant energy that can be sensed or seen by the human eye. Visible light is measured in lumens.
Light Center Length (L.C.L.)
The distance between the center of the filament, or arc tube, and a reference plane ’Äî usually the bottom of the lamp base. Refer to the following chart for reference plane locations.
Light Emitting Diodes (LED)
A solid-state semiconductor device that converts electrical energy directly into light. On its most basic level, the semiconductor is comprised of two regions. The p-region contains positive electrical charges while the n-region contains negative electrical charges. When voltage is applied and current begins to flow, the electrons move across the n region into the p region. The process of an electron moving through the p-n junction releases energy. The dispersion of this energy produces photons with visible wavelengths.
Louver
A series of baffles used to shield a source from view at certain angles or to absorb unwanted light. The baffles are usually arranged in a geometric pattern.
Low Flux
LEDs that are typically .1 to .4 watts each, and are arranged in clusters or arrays to create a collective light source. These systems operate a 12vdc or 24 vdc.
Low Power Factor Ballast (LPF)
Ballast with a power factor of 0.79 or less - also called normal power factor (NPF) ballast. LPF ballast requires about twice the line current of HPF ballast so fewer LPF ballasts can be installed on a circuit, which increases installation cost.
Lumen
A measure of the luminous flux or quantity of light emitted by a source. For example, a dinner candle provides about 12 lumens. A 60-watt Soft White incandescent lamp provides about 840 lumens.
Lumen Depreciation
The decrease in lumen output of a light source over time. Also see Lumen Maintenance.
Lumen Maintenance
A measure of how well a lamp maintains its light output over time. It may be expressed numerically or as a graph of light output vs. time.
Lumens Per Watt (lpW)
A ratio expressing the luminous efficacy of a light source.
Luminaire
A complete lighting unit consisting of a lamp (or lamps), ballast (or ballasts) as required together with the parts designed to distribute the light, position and protect the lamps and connect them to the power supply. A luminaire is often referred to as a fixture.
Luminaire Efficiency
The ratio of total lumens emitted by a luminaire to those emitted by the lamp or lamps used in that luminaire.
Luminance
A photometric measure of "brightness" of a surface as seen by the observer, measured in candelas per square meter.
Luminous Efficacy
The light output (lumens) of a light source divided by the total power input (watts) to that source. It is expressed in lumens per watt.
Typical lamp efficacies:
’Ä¢ Thomas Edison's first lamp ’Äî 1.4 lpW
’Ä¢ Incandescent lamps ’Äî 10-40
’Ä¢ Halogen incandescent lamps ’Äî 20-45
’Ä¢ Fluorescent lamps ’Äî 35-105
’Ä¢ Mercury lamps ’Äî 50-60
’Ä¢ Metal halide lamps ’Äî 60-120
’Ä¢ High-pressure sodium lamps ’Äî 60-140
Note: The values above for discharge lamps do not include the effect of the ballasts, which must be used with those lamps. Taking ballast losses into account reduces "system" or lamp-ballast efficacies typically by 10-20% depending upon the type of ballast used.
Lux (lx)
A unit of illuminance or light falling onto a surface. One lux is equal to one lumen per square meter. Ten lux approximately equals one footcandle.
> Return to Top