Base or Socket
The socket is the receptacle connected to the electrical supply; the base is the end of the lamp that fits into the socket. There are many types of bases used in lamps, screw bases being the most common for incandescent and HID lamps, while bipin bases are common for linear fluorescent lamps.

A style of bulb base which uses keyways instead of threads to connect the bulb to the fixture base. The bulb is locked in place by pushing it down and turning it clockwise.

Beam Angle
The angular dimension of the cone of light from reflectorized lamps (such as R and PAR types) encompassing the central part of the beam out to the angle where the intensity is 50% of maximum. The beam angle sometimes called "beam spread" is often part of the ordering code for the reflectorized lamps.

Beam Lumens
The total lumens present within the portion of the beam contained in the beam angle.

Any base with two metal pins for electrical contact. This is the typical base for a fluorescent tube of 1 to 4 feet in length. It consists of 2 prong contacts which connect into the fixture. Medium bi-pins are used with type T-8 and T-12 tubular fluorescent lamps, and miniature bi-pins are used for tubular T-5 fluorescent lamps.

Bulb Material or Coating
The type of glass (or quartz) used in the glass envelope surrounding the light source. The material can also have coatings applied to achieve particular performances.

Metal filaments that emit electrons in a fluorescent lamp. Negatively charged free electrons emitted by the cathode are attracted to the positive electrode (anode), creating an electric current between the electrodes.

Colour Rendering Index (CRI)
An international system used to rate a lamp's ability to render object colours. The higher the CRI (based upon a 0-100 scale) the richer colours generally appear. CRI ratings of various lamps may be compared, but a numerical comparison is only valid if the lamps are close in colour temperature. CRI differences among lamps are not usually significant (visible to the eye) unless the difference is more than 3-5 points.

Colour Temperature
A number indicating the degree of "yellowness" or "blueness" of a white light source. Measured in kelvins, Yellowish-white ("warm") sources, like incandescent lamps, have lower colour temperatures in the 2700K-3000K range; white and bluish-white ("cool") sources, such as cool white (4100K) and natural daylight (6000K), have higher colour temperatures. The higher the colour temperature the whiter, or bluer, the light will be.

Compact Fluorescent Lamp
The general term applied to fluorescent lamps 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 4100 K. The Cool White designation is used specifically for T12 and other fluorescent lamps using halophosphors and having a CRI of 62.

Daylight Lamp
A lamp resembling the colour of daylight, typically with a colour temperature of 5500 K to 6500K.

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

A measurement of how effective the light source is in converting electrical energy to lumens of visible light. Expressed in lumens-per-watt (LPW) this measure gives more weight to the yellow region of the spectrum and less weight to the blue and red region where the eye is not as sensitive.

The efficiency of a light source is simply the fraction of electrical energy converted to light, i.e. watts of visible light produced for each watt of electrical power with no concern about the wavelength where the energy is being radiated. For example, a 100 watt incandescent lamp converts 7% of the electrical energy into light; discharge lamps convert 25% to 40% into light. The efficiency of a luminaire or fixture is the percentage of the lamp lumens that actually comes out of the fixture.

Metal tungsten wire heated by the passage of electrical current, used to emit light in incandescent lamps. In fluorescent lamps the filament is coated with emission mix and emits electrons when heated.

Filament Voltage
Filaments are designed to get to operating temperature when an appropriate voltage is applied, e.g. 120 volts or 12 volts in the case of incandescent lamps or MR16 lamps. In certain fluorescent lamps the filament voltage is the low voltage applied to the cathode to energize it for electron emission.

A luminaire used to light a scene or object to a level much brighter than its surroundings. Usually floodlights can be aimed at the object or area of interest.

A physical phenomenon whereby an atom of a material absorbs a photon of light an immediately emits a photon of longer wavelength. If there is a significant delay the phenomenon is called phosphorescence rather than fluorescence. It is interesting that "phosphors" used in lamps exhibit "fluorescence," not "phosphorescence."

Fluorescent Lamp
A high efficiency lamp utilizing 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 which makes up the structure of the lamp. The phosphors transform the UV to visible light.

Full Spectrum Lighting
marketing term, typically associated with light sources that are similar to some forms of natural daylight (5000K and above, 90+ CRI), but sometimes more broadly used for lamps that have a smooth and continuous colour spectrum.

High Power Factor
A ballast whose power factor is corrected to 90% or greater by the use of a capacitor.

Input Voltage
Power supply voltage required for proper operation of fluorescent or HID ballast.

Input Watts
The total power input to the ballast which includes lamp watts and ballast losses. The total power input to the fixture is the input watts to the ballast or ballasts and is the value to be used when calculating cost of energy and air conditioning loads.

Lamp Height
Referenced by IEC as Dimension C. Also referred to as "Base Face to Top of Lamp".

Light Loss Factor
The product of all factors that contribute to lowering the illumination level including reflector degradation, dirt, lamp depreciation over time, voltage fluctuations, etc.


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 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.

Luminaire Efficiency
The ratio of total lumens emitted by a luminaire to those emitted by the lamp or lamps used in that 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.

A measure of "surface brightness" when an observer is looking in the direction of the surface. It is measured in candelas per square meter (or per square foot) and was formerly referred to as "photometric brightness."

Maximum Overall Length (M.O.L.)
The end-to-end measurement of a lamp, expressed in inches or millimetres.

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.

PCB (Polychlorinated Biphenyls)
Chemical pollutant formerly used in ballast capacitors that were part of ballasts. It is now illegal to use PCB's and most such ballasts have been replaced over time.

An inorganic chemical compound processed into a powder and deposited on the inner glass surface of fluorescent tubes and some mercury and metal-halide lamp bulbs. Phosphors are designed to absorb short wavelength ultraviolet radiation and to transform and emit it as visible light.

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

Power Factor Corrected
Ballasts that incorporate a means of Power Factor Correction but whose power factor is 90% or greater.

Rapid Start
Lamp starting method in which lamp filaments are heated while open circuit voltage (OCV) is applied to facilitate lamp ignition.

The ratio of light reflected from a surface to that incident upon it.

Starting Temperature (Minimum)
The minimum ambient temperature at which the lamp will start reliably.

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.

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.

Warm White
Refers to a colour temperature around 3000K, providing a yellowish-white light.