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Glossary of Lighting Terms

Aluminium Reflector

Many spot and flood lamps are manufactured using a thin film of reflective aluminium deposited on the inside of the glass.



A popular term for lamps derived from the bulb-shaped glass envelope in which lamps are often enclosed



The unit of luminous intensity, describing light output in a given direction



The electrical connection and mechanical fixing for a lamp is usually referred to as a cap, base or fitting.


Colour Rendering Index (CRI)

An indication of a light sources ability to render colour accurately. The rating is a number between 1 and 100. The higher the number, the more accurate the colour rendering. CRI does not describe the colour appearance of the light source.


Colour Temperature

The colour temperature of a light is a measure of the warmth or coldness of the light it produces. This is measured in Kelvins (K). The lower the number is the warmer the colour and the higher the number is the cooler the colour. For example:

Warm: colour temperatures of less than 3500K

Cool: colour temperature between 3500K and 5000K

Cold/Daylight: colour temperature over 5000K


Connected Load

The entire electrical load including gear losses as connected to the mains supply. This is the load that the electricity meter will record.


Control Equipment

Any type of device that provides some type of regulation to the power that is delivered to the lamp. This includes power supplies, drivers, ballasts and transformers


Cover Glass

A glass panel that covers the front of the luminaire or lamp, to minimise moisture or dust entering it, to control UV or to minimise the risk of injury from the rare instance of an exploding lamp



A technique one of two lamps in a twin fitting is removed or is twisted in the lampholder to disconnect it from power



The amount of light obtained from the energy used. Efficacy is measured in lumers per watt (lm/W)



The effect of brightness or differences in brightn3ess within the visual field that is high enough to cause annoyance, discomfort or loss of visual performance


Illuminance (Lux/lx)

Lux is a unit of illumination of one square metre, which is one metre away from a uniform light source. It is also a European standard of measurement.


International Electrotechnical Commission (IEC)

The International Electrotechnical Commission is the authoritative worldwide body responsible for developing consensus global standards in the electrotechnical field. IEC is dedicated to the harmonization and voluntary adoption of these standards, supporting the transfer of electrotechnology, assisting certification and promoting international trade



The percentage of lumens that an LED lamp will produce after a certain number of operating hours, compared to when the lamp was new. In this case the lamp would produce 70% of the initial lumens



The official term for the light source that is often referred to as a LightBulb



The component of the luminaire that provides electrical connection to the lamp. In some cases the lampholder holds the lamp in a fixed position


Leading Edge

These dimmers are able to reduce the load by shortening the cycle at the leading edge of the input waveform. Most commonly used with Incandescents or Halogens



A light-emitting diode (LED) is a semiconductor light source. The light source is provided from an LED chip


Light Output Ratio (LOR)

The ratio of the amount of light emitted by the luminaire in relation to the amount of light produced by the lamp and usually expressed as a percentage. LOR expresses the efficiency of a luminaire


Lumen (lm)

The total light output of a light source in all directions. Also known as luminous lux



The general term for the fitting where a lamp is installed. This will always include a lamp holder with the electrical connection to the lamp and may also include shades, reflectors or diffusers along with decorative, protective and/or safety features


Luminaire Efficiency

Expresses how much of the light produced by the light source is able to leave the luminaire and provide light into the environment. Often expressed as the light output ratio (LOR).



A measurement of the brightness of a light source or a surface that is illuminated. Luminance is directly influenced by the characteristics of the surface and is measured in candelas per square metre



See Illuminance



The hardware used to control produced light. This control is typically delivered by refraction, using lenses and diffusers



A series of measurements of the light distribution of a luminaire or lamp. Usually expressed in a table generated by a testing laboratory, These data have been standardised into a few formats so that they can be incorporated into computer-based lighting design calculations. The most common form of these is the IES format. A photometric file is a computer file containing data on the light distribution performance of a luminaire. These files can be used with lighting design software packages predict the effect of a particular light fitting a space



Pulse-start is a specific matched system of lamps and ballasts designed to provide very high efficiency



Replacement of lamps after a predetermined period of use, typically 80% of the rated life


Stepped Switching

Dimming pre-set to occur at a certain percentage(s) of light output


Trailing Edge

These dimmers are designed to fade the voltage to zero rather than switch it abruptly off by applying a resistance to create a ramp. This increases the amount of heat dissipated since the resistance period generates heat.


Useful Lumens

This only applies to spotlights as they provide directional light. Useful lumens are tested by measuring the amount of lumens in a 90 degree cone. Also known as 'Directional Light'


Volt (V)

Volts is the unit measuring the electric current (in this case) used to power a bulb. Most bulbs are designed to work with mains voltage (240v). However, low voltage bulbs will usually require a transformer/driver


Watt (W)

The unit for measuring electrical power. Watts used multiplied by a time period forms the basis of one of the elements of our electricity billing, typically shown as kilowatt hours (kWh). The wattage is also related to the brightness of the lamp but is not a measurement of brightness


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