LED Guide

CCT(Correlated Colour Temperature):

A number indicating the degree of “yellowness” or “blueness” of a white light source. Measured in kelvins, CCT represents the temperature an incandescent object (like a filament) must reach to mimic the colour of the lamp. Yellowish-white (“warm”) sources, have lower colour temperatures in the 2700K-3000K range; white and bluish-white (“cool”) sources, such as cool white (4000K) and natural daylight (6500K), have higher colour temperatures. The higher the colour temperature the whiter, or bluer.

Compact Fluorescent Lamp (CFL):

The general term applied to florescent lamp that are single-ended and that have smaller diameter tubes that are bent to form a compact shape. Some CFLs have integral ballasts and medium or candelabra screw bases for easy replacement of incandescent lamps.

Cool White:

A term loosely used to denote a colour temperature of around 4000K.

DALI (Digitally Addressable Lighting Interface):

An industry standard system protocol that allows components from different manufacturers (ballasts, controls systems, sensors, controllers, switches, etc) to be mixed together seamlessly into complete systems.

Daylight Lamp:

A lamp resembling the colour of daylight, typically with a colour temperature of 6500K.


Whether or not the lamp lumens can be varied while maintaining reliability.

Discharge Lamp:

A device that produces light by using an electric arc, rather than a filament, to create illumination.


Lumen output per unit of power supplied to the lamp (lumens per watt).

Electromagnetic Ballast:

A low frequency (50 or 60 Hz) ballast that uses a “Core and Coil” assembly to transform electrical energy (voltage and current) to start and operate fluorescent and high-intensity discharge (HID) lamps.


Coated coil of special wire that emits electrons or light when heated.

Filament Voltage:

Voltage applied to heat the lamp filament coil. Also called electrode or filament heating.


Functional grouping that limits interference feedback into the power source and protests internal ballast components.

Flux / Luminous Flux:

Luminous flux is the measure of the perceived power of light, adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light.


Emission of visible light by the absorption of energy from another source.

Fluorescent Lamp:

A halogen lamp is an incandescent lamp with a filament that is surrounded by halogen gases, such as iodine or bromine. Halogen gases allow the filaments to be operated at higher temperatures and higher efficacies. The halogen participates in a tungsten transport cycle, returning tungsten to the filament and prolonging lamp life.

Footcandles (fc):

Measure of light level on a surface that is being illuminated.

Halogen Lamp:

A halogen lamp is an incandescent lamp with a filament that is surrounded by halogen gases, such as iodine or bromine. Halogen gases allow the filaments to be operated at higher temperatures and higher efficacies. The halogen participates in a tungsten transport cycle, returning tungsten to the filament and prolonging lamp life.

High Intensity Discharge (HID) Lamp:

A lamp containing a filled arc tube in which the active element becomes vaporized (a gaseous state) and is discharged into the arc stream to product light.

High Pressure Sodium (HPS) Lamp:

High Intensity Discharge light source which produce light by an electrical discharge sodium vapor operating at relatively high pressures and temperatures.

Initial Lumens:

The measure of the amount of light a lamp produces after it has been operating 100 hours.

Instant Start:

An electromagnetic or electronic lighting circuit without lamp filament heating that produces instant light.

Lamp Types:

Whether reliFilament lamps: Incandescent, Halogen, Halogen-IR.

Discharge Lamps: Fluorescent, HID (High Intensity Discharge) HID Lamps: Mercury, HPS (High Pressure Sodium), MH (Metal Halide) and CMH.

LED Chip (Chip):

The light producing semiconductor device that may or may not be incorporated into an LED.

LED Driver:

An electronic circuit that converts input power into a current source ¡ª a source in which current remains constant despite fluctuations in voltage. An LED driver protects LEDs from normal voltage fluctuations, overvoltages, and voltage spikes.

LED Luminaire:

A complete lighting unit consisting of LED-based light emitting elements and a matched driver together with parts to distribut light, to position and protect the light emitting elements, and to connect the unit to a branch circuit. The LED based light emitting elements may take the form of LED packages, (components), LED arrays (modules) LED Light Engine, or LED lamps. The LED luminaire is intended to connect directly to a branch circuit

Light Emitting Diode (LED):

A Light Emitting Diode (LED) is 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.

Lumen Depreciation:

The decrease in lumen output of a light source over time. Also called Lumen Maintenance.

Lumen Maintenance:

The rate at which light output declines over time.


The international (SI) unit of luminous flux or quantity of light and equals the amount of light that is spread over a square foot of surface by one candle power when all parts of the surface are exactly one foot from the light source. For example, a dinner candle provides about 12 lumens.


A light fixture; the complete lighting unit, including lamp, reflector, ballast, socket, wiring, diffuser, and housing.

Luminous Efficacy:

The light output of a light source divided by the total power input to that source. Expressed in lumens per watt.

Lux (lx):

A unit of illuminance or light falling onto a surface. One lux is equal to one lumen per square meter.

Mercury Lamp:

A High Intensity Discharge (HID) light source in which the light is produced by radiation from mercury, plus halides of metals such as sodium, scandium, indium and dysprosium.

Mounting Height:

Distance from the bottom of the fixture to either the floor or work plane, depending on usage.

MR-16 and MR-11:

A line of low voltage compact reflector lamps used for accent and spot lighting. The 16 and 11 refer to 16 eighths of an inch diameter and 11 eighths.

Parallel Lamp Operation:

Refers to ballasts that employ multiple output current paths from a single ballast to allow lamps to operate independent of one another, allowing other lamps operated by the ballast to remain lit should companion lamp(s) fail.

PAR Lamp:

PAR is an acronym for parabolic aluminized reflector. A PAR lamp, which may utilize either an incandescent filament, a halogen filament tube or a HID arc tube, is a precision pressed-glass reflector lamp. PAR lamps rely on both the internal reflector and prisms in the lens for control of the light beam.

Preheat Ballast:

Electromagnetic ballast that requires separate starter in order to ignite the lamp.

Power Factor:

Measurement of the relationship between the AC source voltage and current. High power factor ballasts require less AC operating current at the same wattage than an equivalent low power factor ballast.


Power Factor equals Input Watts divided by the product of Line Volts times Line Amps (Volt Amps or VA).

Rapid Start Lamp:

Fluorescent lamp that requires filament heating before igniting and producing light.

Reflector Lamp (R):

A light source with a built-in reflecting surface. Sometimes, the term is used to refer specifically to blown bulbs like the R and ER lamps; at other times, it includes all reflectorized lamps like PAR and MR.

T-12, T-8, T-5:

A designation for the diameter of a tubular bulb in eighths of an inch; T-12 is 12 eighths of an inch, or 11/2 inches; T-8 is 1 inch, and so on.

Starting Temperature:

The minimum ambient temperature at which the lamp will start.


Spiraling or swirling of fluorescent lamps at initial turn on or energy-saving lamps at low temperature or low current.


Transients are sudden but significant deviations from normal voltage or current levels.

Ultraviolet (UV):

Electromagnetic radiation with wavelength shorter than that of visible light.

Voltage (V):

A, measure of electrical potential, express in volts (V).

Warm White:

A description of light with a correlated color temperature between 3000K and 3500K, usually perceived a slightly yellow