Glossary of  LED Terminology

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-10V (sometimes also called 1-10V) dimming is an analogue based system for dimming and lighting controls. The LED driver is controlled by a low power DC input line (0 to 10V DC), which is fed from the dimmer module. This system is not limited by total system power consumption, and it is therefore possible to run large quantities of fittings on one circuit.

Circuit watts

Circuit watts (Wcct) means the amount of watts used to power a complete circuit including the driver and the LED chips, rather than just a luminaire.

Colour temperature

Colour temperature is used to describe whether a light source appears ‘warm’, ‘natural’ or ‘cool’. Colour temperature is measure using the Kelvin scale (K). ±3000k – warm white is considered appropriate for domestic settings. ±4000k – natural white is used more often in retail and office environments. ±6000k – cool white gives a more clinical “high tech” feel – perfect for outdoor lighting, it also helps improve images on CCTV. The higher the colour temperature, the ‘cooler’ the appearance.


Colour Rendering Index is the ability of a light source to show the colours of an object correctly. Lamps with poor colour rendering will distort some colours, meaning that you may think you have purchase a lovely mid to deep red jumper, but in reality, it’s actually a vibrant red. CRI is rated by 0-100, the higher the CRI the more accurately the lamp will show colours. Specific colours may be important for the viewer, CRI comprises the total light spectrum, R values are the individual colours within the spectrum, for example the R9 value – this is the amount of red present within the light spectrum. The higher the R9 value, the more accurate red objects will appear.


The Digital Addressable Lighting Interface is a protocol for dimming and lighting controls designed to an agreed standard as set by the lighting industry. The LED driver is connected to a DALI control interface which in turn is controlled by the main system, whether a mechanical dimmer or a dedicated or generic computer. Each fitting can be individually addressed and completely automated for control, either for real time dimming or automatic on-off / dimming timer control.

Daylight harvesting

Controls the light output of the luminaire by dimming depending upon how much ambient light is shining on the sensor, which is integral to the fitting. It is used to stabilise the ambient light in an area to ensure a constant light level is achieved in the environment – thus neither over or under lighting, optimising energy usage and localising control to the immediate surrounding area - used mainly on indoor lighting in commercial and industrial areas with available natural daylight.

Daylight sensor

Changes the state of its internal switch from on to off or vice versa depending upon how much ambient light is shining on the sensor. It is used to control when a light should switch on or off depending upon the darkness of the surrounding environment – used mainly on outdoor lighting to save energy.

Emergency lighting

Every commercial or industrial building should have emergency lighting for safety and security reasons. Non-maintained emergency lighting only comes on when the main power supply fails; it is used to illuminate key emergency exit routes. Maintained emergency lighting is used as a regular daily luminaire taking its power from the mains power source; however in a power cut the emergency mode takes over and the power is taken from a contained back up battery.

Inrush current

LED lighting devices consume an increased level of current at switch on – this can be up to 5 times the standard steady state operating current and lasts for microseconds (µs) This is due to the charging current of the input capacitance. This inrush current is safe and relates to the device input current as fed by the AC mains supply, it is only a concern when considering circuit protection, as outlined below. The selection of overcurrent protection devices such as fuses and circuit breakers is very important, as the overcurrent protection must react quickly to overload or open circuit however must not interrupt the circuit when the harmless inrush current flows.


The kilo-watt hour is a unit of energy equal to 1,000watt-hours. This is how many thousands of watts a device uses in one hour. Electricity bills are calculated using kWh.


Lux is the international unit of luminance – a measurement of how much luminous flux (lumens - lm) is spread over any given area (in square meters – m²). This measurement will tell you how much light will arrive at a surface, where 1lm/m² =1lx(lux).


Short for Passive InfraRed, PIR sensors are electronic sensors that measure infrared light radiating from objects in their field of view. It can detect heat from objects which would otherwise be undetectable by humans. PIR sensors are one of the main technologies used in presence and absence detection, in order to turn lights on or off depending on whether people are present or not. Many detectors also include daylight sensors.


Triac dimming uses either leading or trailing edge technology for dimming and lighting controls. This is an analogue system and functions by ‘chopping’ the AC power to reduce the input voltage to the lamp.