The Lighthouse UK (FSL Direct) Ltd - Lighting Glossary

Arc discharge (in a gas or vapor):-
Electrical discharge characterized by a cathode fall that is small compared with that in a glow discharge.

Average Illuminance:-
Illumination averaged over a specified surface.

Ballast:-
Electrical or Electronic component used with discharge lamps for stabilizing the current in the discharge.

Ballast lumen factor:-
Refers to the ratio of light output from the lamp on an emergency operation to the nominal light output.

Beam spread:-
the angle (in the plane through the beam axis) over which the luminous intensity drops to a stated percentage of its peak intensity.

Brightness:-
The subjective perceived illumination.

Candela (cd):-
The unit of luminous intensity.

Colour rendering index RA:-
A measure of the degree to which the colour rendition of a light source differs on average from that of a lamp. At RA (8) the illuminant (perceived) colour shift of eight reference colours is measured to give one number. Values of 100-90 are very good and lamps with RA’s of 80 should not be used where people are working continuously.

Colour temperatureT (K):-
Black bodies (as with most others) when heated sufficiently will emit red light, when the temperature is increased further still the emitted light becomes white. The colour co-ordinates derived from this heated black body when plotted on a diagram lie on a smooth curve known as the full radiator locus, and are shown on the CIE Chromacity Diagram. The colour appearance of a given light source can be compared to a position on the full radiator locus by reference to its colour temperature, and is generally quoted in degrees Kelvin.

Dimming:-
A procedure of varying the luminous flux from lamps in a lighting installation, by way of an electrical or electronic component.

Discharge lamp:-
Lamp in which the light is produced, directly or indirectly, by an electric discharge through a gas, a metal vapour, or a mixture of several gases and vapours.

Emergency lighting:-
Lighting provided for use(usually evacuation of premises) when the electrical supply to the normal lighting fails.

Flicker:-
Impression of fluctuating luminance or colour.

Fluorescent Tube:-
Low pressure mercury discharge lamp type in which most of the light is emitted by a layer of fluorescent material (phosphor coating) electrically charged by the U.V. radiation from the discharge source.

Fluorescent mercury lamp:-
High-pressure mercury lamp in which the light is produced by both the mercury vapour and by a phosphor coating on the inner surface of the outer envelope which is electrically charged by the U.V. radiation of the discharge source. References such as MBFT, HQL Super De Luxe and HQL De Luxe refer to Fluorescent Mercury Lamps.

Glare:-
Glare is the discomfort caused by high luminances in the field of vision.

Light:-
Electromagnetic radiation with a wavelength of between 380-720nm. Ultraviolet light has a wavelength of less than 380nm whilst infrared light is greater at 720nm. i.e the cooler and warmer end of the lighting spectrum.

Lighting Level:-
The incidence of light flux on a surface per unit of area, measured in lux. There is a difference between the vertical and horizontal lighting level.

Lumen (lm):-
Unit of luminous flux used to describe a quantity of light emitted by a source or received by a surface.

Luminance:-
The measure of brightness with which the eye perceives an illuminated surface from a certain direction. The luminous intensity per unit of visible surface of a light source (direct light) or an illuminated surface (reflection or indirect light) Luminance is indicated in candelas per square metre (cd/m2)

Lux:-
The unit of illuminance, equal to one lumen per square metre (lm/m2)

Halogen lamp:-
Halogen filled lamp containing a tungsten filament.

High-pressure mercury (vapour) lamp:-
Mercury vapour lamp, with or without a coating of phosphor, in which during operation the partial pressure of the vapor is of the order of 105 Pa - for example: HPL and HPL-N lamps.

High-pressure sodium (vapour) lamp:-
Sodium vapour lamp in which the partial pressure of the vapour during operation is of the order of 104 Pa - for example, SON and SON-T lamps.

Incandescent lamp:-
Lamp in which an electric current is passed through a filament thus creating heat. The light is the glow produced.

Low-pressure mercury (vapor) lamp:-
Mercury vapor lamp, with or without a coating of phosphor, in which during operation the partial pressure of the vapor does not exceed 100 Pa - for example a 'TL' lamp.

Low-pressure sodium (vapor) lamp:-
Sodium vapor lamp in which the partial pressure of the vapor during operation does not exceed 5 Pa - for example a SOX lamp.

Metal halide lamp:-
Discharge lamp in which the major portion of the light is produced by the radiation from a mixture of a metallic vapour (for example, mercury) and the products of the dissociation of halides (for example, halides of thallium, indium or sodium) - for example: HCI-T/HQI-TS lamps.

Metal vapour lamp:-
Discharge lamp such as the 'mercury (vapor) lamp' and the 'sodium (vapor) lamp' in which the light is mainly produced in a metallic vapor.

Power Factor Correction (pfc):-
Electricity supply require that the companies require that the power factor at which the supply is used shall be maintained at not less than 0.9 lagging, on average between one meter reading and the next. For any given wave shape, the power factor is defined as the ratio of Watts/(volts rms x ampsrms) Low power factors increase the KVa demand from the supply, reduces the useful load that can be safely handled by the cables and distribution equipment, and in some cases can attract additional tariff penalties. Lamp circuits which incorporate a choke, leakage reactance transformer, or an electronic ballast can have low power factors, often between 0.3 and 0.6. Low power factor from these circuits can be corrected by the addition of a compensation capacitor. These can be placed at the central point of the supply, locally for each group of luminaries , or integral within each luminaire.

Projector:-
Luminaire using reflection and/or refraction to increase the luminous intensity within a limited solid angle.

Reflector lamp:-
Lamp in which part of the bulb is coated with a reflecting material, either diffuse or specular, so as to control the light, for example: HPL-R, MLR, and 'TL'F lamps.

Spotlight:-
A (small) concentrated light source of usually not more than 20° divergence, giving an intense beam of light over a short to medium

Spread:-
Quantity of a luminaire to indicate the extent to which the light is 'spread out'. Luminaires are classified as being of narrow, average or broad spread.

Starter:-
Device for starting a discharge lamp (in particular a fluorescent lamp) that provides for the necessary preheating of the electrodes and/or causes a voltage surge in combination with the series ballast.

Switch-start fluorescent lamp:-
Fluorescent lamp suitable for operation with a circuit requiring a starter for the preheating of the electrodes, for example 'TL'D type.