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When it comes to lighting, there's a lot of language and a lot of acronyms to figure out. We aim to make finding the appropriate product as simple as possible, so we've compiled a dictionary of all the lighting words and acronyms you might come across when exploring our site.
AC (~)

Alternating Current, as found in the mains power supply.

Also commonly called display or highlighting. Accent lighting is typically at a higher intensity to emphasise an object or area. A Ratio of 3:1 versus ambient lighting is recommended for accent lighting to be noticeable.

Ambient Lighting

Alternating Current, as found in the mains power supply.

Ambient Temperature (Ta)

The air temperature surrounding the luminaire or component. LED luminaires are particularly temperature-sensitive with excess temperature affecting performance and rated life. See also Junction Temperature.

Ampere (Amp)

The unit for measuring rate of flow of electrical current: Current (Amps) = Power (Watts) / Voltage(Volts).

Asymmetric Light Distribution

Where the distribution of light from a luminaire is not even in one plane. Common in display luminaires such as ‘wall washers’ where light is directed intentionally in one direction.


The ‘swivel’ angle, as used in floodlighting or display lighting designs and installations.

Ballast Lumen Factor (BLF)

The proportion of light emitted by a luminaire when in emergency mode, usually powered by batteries, compared to the normal mains powered output. BLF figures can be less than 10% or 0.1 as emergency lighting levels are far lower than those required for normal lighting.

Bathroom Zones

Bathroom lighting needs to be functional and safe. It is divided into zones where only suitable light fittings should be used.

Zone 0 is inside the bath or shower. Any fitting used in this zone must be low voltage, (max 12v) and rated at least IP67 which is immersion proof.

Zone 1 is the area above the bath to a height of 2.25m from the floor. In this zone, a minimum rating of IP44 is required.

Zone 2 is the area stretching 0.6m outside the perimeter of the bath and the area between zone 1 and the ceiling up to 3m. Also, the area around the washbasin is within a 60cm radius of any tap. In this zone, a minimum rating of IP44 is required.

Class I

Class one luminaires require an Earth connection for electrical safety.

Class II

Class one luminaires require an Earth connection for electrical safety.

Colour Appearance

A term used to describe how “white” the emitted light looks. Commonly, warm, neutral, cool, and daylight are used to categorise.

Colour Rendering Index (CRI)

A measure of the degree of colour shift objects undergoes when illuminated by the light source as compared with those same objects when illuminated by a reference source of comparable colour temperature. The reference source has a CRI of 100. Natural light (daylight) would also be 100.

Double Insulation

Also known as Class II, where two levels of insulation (such as two cable coverings) protect live parts from exposure.


The driver is often the critical component in a LED luminaire or lamp, more so than the LED chip itself. The driver has to be matched to the power requirements of the LED chip and also have quality components. Drivers that use inferior components such as capacitors, will fail before the rated life of the LED chip, reducing the claimed life by as much as 50%.

Edge Lit

This means that the LED chips are positioned vertically around the perimeter of the panel. This provides an excellent uniformly illuminated panel in a fixture as slim as 8mm.

Edison Screw

A lamp cap that features a screw thread for a positive fit in the lamp holder, common sizes include E15 and E27.


Is the measure of how efficient a lamp or luminaire is. This can be expressed as (source) lumens per Watt, which is the normal measure for lamps. Or, as luminaire lumens per circuit Watt, which is common for luminaires. The figure for luminaires will also include the LOR of the luminaire in the calculation.

Emergency Lighting

Allows the safe evacuation of an area in the event of a mains failure. The positioning and number of emergency lighting luminaires are detailed in British Standard BS5266. It is vital that emergency lighting is maintained correctly to ensure batteries are conditioned, so it operates when required.

Escape Route

Emergency lighting along a route such as a corridor or staircase to enable safe evacuation

F Mark

Denotes luminaires that can be mounted on flammable surfaces as the heat generated will not cause any combustion. Previously luminaires that were suitable had to be marked, but the most recent standard requires only luminaires that don’t comply to be marked.

Fire Rated

Where a luminaire is installed in a fire barrier such as into a ceiling, it must have the same resistance to fire rating as that barrier. For domestic installations, there are ratings of 30, 60, and 90mins and each limit must be tested for. A 90min rated product does not automatically comply with 30 or 60mins due to the different ceiling constructions. Non-domestic applications usually have a fire-resistant barrier such as a concrete slab between floors and so do not have the requirement in many cases.

Flux/Luminous Flux

Luminous flux is the measure of the perceived power of light, adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light and is expressed in Lumens (lm).

Frequency (Hz)

Rate that the power supply wavelength fluctuates and is measured in Hertz.

General Lighting

Lighting to illuminate the general area without supplementary task lighting.


Difficulty seeing in the presence of bright light such as direct or reflected sunlight or artificial light. Proportional to the background illuminance; a good example is a car headlight that creates glare at nighttime but not during the day.


A photometric device for testing the luminous intensity distribution, efficiency, and luminous flux of luminaires.

Heat Sink

A part of the thermal system that conducts or convects heat away from sensitive components, such as LEDs and electronics.

Hertz (Hz)

The unit to measure frequency.

High Power LED

A high power LED, sometimes referred to as a power LED, is one that is driven at a current of 350mA or higher.

High Risk Area

A requirement in emergency lighting where a process may require safe shut down or an increased hazard. Higher emergency lighting levels are therefore required local to the risk.


Illuminating Engineering Society, an American organisation that provides standards and recommendations. Photometric data files are commonly in .ies file format.


The intensity of light falling on a surface area. If the area is measured in square feet, the unit of illuminance is footcandles (fc). If measured in square meters, the unit of illuminance is lux (lx).

Indirect Lighting

Lighting that is reflected by room surfaces or within the luminaire before falling on to the working area. As a result of reflection it is often lower in intensity and glare.

Ingress Protection (IP) Rating

A system that identifies the protection that a lamp or luminaire has against solid objects and water. The first digit being solid object protection and the second one resistance to water.

Initial Lumens

The output up to 100 hours use.

Inrush Current

Components such as drivers can have high inrush currents for milliseconds due to the use of capacitors; this should be considered when specifying switching and breaker ratings.

Integrating Sphere

A device used for a variety of optical, photometric, or radiometric measurements.

Isolux Diagram

A graphical representation of common illuminancelevels to show lighting levels over a calculated area.


The point at which the positive and negative conductors meet in a LED.

Junction Temperature

A critical consideration in LED lamp or luminairedesign. For every 10°C that the junction temperature exceeds the optimum figure, life of the LED chip is reduced by 50%. Overrunning LEDs by operating at higher amps will cause this to happen.


The SI unit used to measure and denote colour temperature, degrees Kelvin.


Kilo-Watt-hour is the typical billing unit for electricity costs and represents 1kW of power over a 1 hour duration.


A lamp converts electrical power into light and sometimes they are called “bulbs” due to the traditional lamp shape.


Light Emitting Diode. An LED is a solid-state semiconductor device that converts electrical energy directly into light. On its most basic level, the semiconductor is comprised of two regions. The p-region contains positive electrical charges while the n-region contains negative electrical charges. When voltage is applied and current begins to flow, the electrons move across the n-region into the p-region. The process of an electron moving through the p-n junction releases energy. The dispersion of this energy produces photons with visible wavelengths. Most LEDs emit blue light as that is the most efficient format, a phosphor coating turns the blue light into the white light required.

LED Rated Life

LED chip figures are quoted by the chip manufacturer and in some cases, these are not translated when the chip is used in a luminaire, where it can run hotter. As heat affects the LED chip, life can be reduced dramatically.

Light Output Ratio (LOR)

Percentage difference between the luminous flux emitted by the light source and the amount emitted from the fixture it is housed in.


Luminaire lumens per circuit Watt is total lumens emitted from the luminaire (source lumens x LOR) / total luminaire wattage including control gear.

Lumen Depreciation

Describes the percentage of light lost relative to the initial lumen output. LEDs depreciate at a far slower rate than other light sources, so a LED with a lower initial output can quickly provide more light than a faster depreciating light source.

Lumen Maintenance

The luminous flux at a given time in the life of the LED. This is expressed as a percentage of the intial luminous flux. This usually determines the rated life of a LED product as the point it should be replaced.

Lumens (lm)

The international (SI) unit of luminous flux. Lumens will become the measure of light output as Watts cannot be a reliable measure due to the different efficacy of light sources and the ongoing improvement in LED efficacy through development.


A lighting fixture complete with installed lamps or light source.

Luminaire Lumens (Llm)

The light emitted from a luminaire will typically differ from the source lumens. This can be from losses within the luminaire housing. Also it is common for LEDs to operate at a higher temperature in the luminaire; this can lead to the output increasing when compared to the source (chip) lumens. Luminaire lumens = source lumens x LOR

Luminaire Wattage

Total wattage of LED and any control gear included.


The surface brightness of an object measured in candelas/m².

Luminous Efficiency

The percentage of total lamp lumens that a lighting fixture, luminaire, or system emits, minus any blocked or wasted light.

Lux (lx)

The SI (International) unit of illuminance, or luminous flux incident on a unit area, frequently defined as one lumen per square metre (lm/m²).

Maintained Emergency

A Maintained emergency luminaire is able to be used for both general and emergency lighting, a second live cable allows it to be turned on/off as required and detect a mains power circuit failure.

Microwave Sensor

The sensor emits low-power microwaves that form a pattern in the area covered. When movement disturbs the pattern, movement is detected and the sensor turns the light source on. Microwave sensors are only recommended for indoor use as they are sensitive to movement and not heat.

Non-Maintained Emergency

A Non-Maintained emergency luminaire ONLY operates in emergency mode and is not for general lighting.

Open Area

Lighting also called ‘anti-panic’ area lighting is emergency lighting where not a high risk area or escape route.

Organic Light-Emitting Diodes (OLED)

Organic light-emitting diodes (OLEDs) are based on organic (carbon-based) materials. In contrast to LEDs, which are small point sources, OLEDs are made in sheets that provide a diffuse area light source. OLED technology is developing rapidly and is increasingly used in display applications such as mobile phones and PDA screens. However, OLEDs are still some years away from becoming a practical general illumination source.


A coating of phosphorescent material which photons from a royal blue LED pass through, causing those photons to exit with a different colour property.

Photometric Data

A generic term for light output and distribution data for a lamp or luminaire and can be shown in many formats. Generally, data is produced following the IES or ELUMDAT method to provide a .ies or .ldt computer file for use in a lighting design program such as Relux or Dialux. Photometric data is available for a wide selection of BG Electrical luminaires from our downloads page.


Passive Infra-Red sensors detect movement by the change in background temperature as body heat moves into the area.

Power Factor

The active power divided by the apparent power (i.e., product of the rms input voltage and rms input current of a driver).

Power Factor Correction

In an electronic device, such as a LED lighting fixture, a system of inductors, capacitors, or voltage converters to adjust the power factor of electronic devices toward the ideal power factor of 1.0.


Registration, Evaluation, Authorisation and restriction of CHemicals. The EU Directive covers the use of hazardous chemicals used in the maufacturing process and supply of products.

Remote LED Driver

Some LED lights in our range use a remote plug and play LED driver, that offers flexibility to select either a fixed output, dimmable driver or emergency versions, with all being interchangeable.

Remote Phosphor

A phosphor conversion technique in which photons from a royal blue LED pass through a phosphor material that is not attached to the LED chip.


Restriction of Hazardous Substances (2002/95/EC) is an article 95 directive, meaning it is across all European Union member states. Since July 1st 2006 the use of hazardous substances is restricted in products, to prevent environmental harm. The prohibited substances are Lead, Mercury, Cadmium, Hexavalent Chromium, Polybrominated Biphenyls and Polybrominated Diphenyl Ethers. All relevant Luceco products comply.


The most common type of Emergency lightingluminaire, where all of the components are within one Emergency luminaire. This can include gear boxes connected directly to individual luminaires but outside the main luminaire housing. If within 1m, it is classed as self-contained.


Surface-mount LEDs.

Source Lumens (lm)

Source or Chip lumens is the output of the LED array and does not allow for any reduction or increase from the luminaire.

Source Wattage

Could also be referred to as chip wattage – for the LED only and does not include any control gear.

Task Lighting

Localised lighting intended for a specific task.

Thermal Management

Controlling the operating temperature of the product through design, examples include heat sinks and improved airflow.


Fire Retardant Thermoplastic. Diffusers used on emergency lighting luminaires and also certain applications where the percentage of diffusers against the ceiling surface area is calculated must be of Tp(a) material.


Upward Light Output Ratio, the percentage of light emitted from a lamp or luminaire above the horizontal plane.

Ultraviolet (UV)

Electromagnetic radiation with wavelength shorter than that of visible light. LEDs emit minimal UV and therefore do not attract insects or potentially damage sensitive materials illuminated by them.

Utilisation Factor

In lighting design, the proportion of the luminous flux emitted by a light source, which reaches the working plane.


The term used to describe the electrical potential difference between oppositely charged conductors.


The power consumed by the LED.

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When it comes to lighting, there's a lot of language and a lot of acronyms to figure out. We aim to make finding the appropriate product as simple as possible, so we've compiled a dictionary of all the lighting words and acronyms you might come across when exploring our site.