INDO Jargon Buster

Click on the plus signs below to reveal an explanation of each term. This list is just a starting point; we will be adding to it regularly over the coming months and referencing terms between this glossary and across the site

Asymmetric Distribution

A light output whose polar plot changes between C planes – i.e. the forward-backwards throw is different to the left-right throw


Another name for ‘Driver’ (see below)


British Standards Institution


A unit of measurement of luminous intensity.  One candela = the light from one candle at 1m


Colour temperature. Colour temperature is the measurement used to describe whether a light source appears ‘warm’ or ‘cool’ – this is indicated by the correlated colour temperature (CCT). As a rule; the higher the colour temperature, the cooler the appearance – and vice versa


EC Conformity Mark


Compact Fluorescent Lamp


Chip on Board

Compact Fluorescent

A small fluorescent lamp. Also known as CFL.


Colour Rendering Index- measure of the ability of a lightsource to reproduce colours. Metal halide CRI = 65-70. LED CRI = 80. HPS CRI = 20-80. Low pressure sodium = 0


A two-way digital communication system for lighting.  DALI is specified by international technical standards (IEC 62386), so that compliant equipment from different manufacturers is compatible with each other. This allows the controller in a system to communicate with (or “talk to”) slave devices, and for those slave devices to “talk” back, providing valuable control and monitoring features for the end user.

Discharge Lamp

A lamp in which light is produced by passing an electric current through a vapour or gas


Glass or plastic shield through which light is shone. Protects the light source. Also known as a protector.


Usually referring to the dimming or part dimming of a lamp at certain times (.e.g 50% dimmed between 2359-0500)


A driver is a self-contained power supply with outputs matching the electrical characteristics of the light source.  Drivers may offer dimming by means of pulse width modulation circuits and can have multiple channels for controlling different light sources.



Efficiency of a lamp in lumens per watt. (Low pressure sodium = Electromagnetic Compatibility directive- aims to minimise the effect of electromagnetic emissions from equipment on radio and other telecoms equipment


European standard national standard is denoted by a country code in front e.g. BS EN 60598


European Norm Electro-technical Certification


A street light


A measure of the total light emitted from a lamp in all directions. The lumens value for projectors describes its luminous flux – or the total amount of light energy emitted from the lens.


The sensation produced by luminance which is sufficiently greater than the luminance the eyes are used to and which can cause annoyance or discomfort.


High Intensity Discharge lamps. (Incl. Mercury vapour, metal halide, HPS & low pressure sodium


High Pressure Mercury Lamps


High Pressure Sodium Lamps

IK Rating

A measure of the degree of protection against impact – useful for understanding how vandal resistant a unit is

IP Rating

Stands for “Ingress Protection”; a measure of the degree of protection provided against dust and water – higher numbers represent more protection (i.e. a more sealed unit). High IP ratings are important for optical parts of a luminaire to prevent dirt building up inside and reducing the light output. For street lighting, a lower IP rating is usually sufficient for other parts of the luminaire.


Lighting Association-UK


Lamp lumen depreciation


A light-emitting diode (LED) is a semiconductor light source


Lighting Industry Federation


Lamp Lumen Maintenance Factor- ratio of luminous flux emitted by a lamp to the initial luminous flux


A standardised test report showing lumens/efficacy, CCT and light distribution


A standardised test done over at least 6,000 hours producing data that can be used in running a TM21 analysis. The TM21 analysis will give a maintenance value


Luminaire Maintenance Factor- ratio of light output ratio at a given time to the initial light output ratio

Luminaire Efficiency

Ratio between flux of luminaire and lamp


Lux is the standard unit of illuminance – measuring how much luminous flux (in lumens) is spread over a given area. In other words lumens measures the “amount” of visible light present, whereas Lux is a measure of the intensity of illumination over a surface. A given amount of light will illuminate an area more dimly if it is spread over a larger area. 1 lux = 1 lumen per m2

Maintenance Factor (MF)

A factor used in a lighting calculation to take into account light loss due to lamp depreciation, cleaning, yellowing of protector etc.


Metal Halide


A type standard of PECU (see below)


Printed Circuit Board


Polycarbonate – Highly durable material used in fixture lenses.  It is more vandal resistant than glass but needs to be UV stabilised to prevent its natural tendency to yellow with age


Printed Circuit Board (Assembled)


A photocell (photo-electric control unit)


A light sensing device that can be used to control luminaires and dimmers

Power Factor

In AC circuits, the power factor is the ratio of the real power that is used to do the work and the apparent power that is supplied to the circuit. The power factor can get values in the range from 0 to 1


The act of adding a new feature or technology to an existing system. Can provide short payback periods and high return on investments for many applications, and often has the lowest environmental impact in terms of upgrade solutions.


Restriction of Hazardous Substances.  Sometimes referred to as Directive 2002/95/EC and made part of UK law in 2013, this restricts use of certain hazardous substances in electrical and electronic equipment such as lead, mercury, hexavalent chronmium etc.


The distance between columns or light sources, usually defined as a “spacing” to meet a required a lighting class.


High Pressure Sodium Lamps

Single Sided

A configuration of light sources on one side of the road only.

Staggered Lighting

A configuration of light sources that alternate from one side of the road to the other between columns.


Waste arising from electrical and electronic equipment- household luminaires are excluded plus filament lamps