Colour Appearance (Colour Temperature)
A term used to describe how 'white' a light source appears to be. Expressed using the Kelvin temperature scale. Examples are warm white (2700-3000K), cool white (4000K) and daylight (6000-6500K).
Colour Rendering Index (CRI)
A scale from 0-100 that describes the ability of a light source to make objects appear their natural colour, as compared to a reference light source. Expressed as Ra value.
Dimmer, Dimming Control
A dimmer is a device used to lower the light output of a source, usually by reducing the wattage it is being operated at. Dimming controls are popular as energy saving devices. Dimming can be achieved by various methods.
A downlight is a small luminaire, which distributes the light downward, usually recessed in the ceiling.
For light-emitting diodes (LEDs). A driver is a device that regulates the voltage and current powering the source. Can be constant current or constant voltage DC.
A ratio expressing the luminous efficacy of a light source or luminaire. Expressed in lumens/ Watt.
Emergency Lighting is lighting provided for use when the supply to the normal lighting fails.
Downlights that are recessed into a ceiling with a fire rating must have the same fire rating as the ceiling. In domestic installations, the ratings under BS 476 are 30,60 and 90 minutes. Each rating must be tested as the ceiling construction is different. Therefore, a 90 minute rated product does not automatically comply with 30 or 60 minutes.
Used to refer to the beam pattern of a luminaire, which disperses the light over a wide beam angle, typically 40 degrees or more.
Impact Protection Rating (IK Rating) is the international standard classification system that indicates the degree of protection provided by an electrical enclosure against external mechanical impacts, in accordance with EN 62262. The code has a number between 00 and 10. The higher the number, the higher the level of impact protection.
The method of lighting a space by directing the light from a luminaire upwards towards the ceiling. The light reflected from the ceiling produced a soft, diffused illumination for the entire area.
Ingress Protection Rating (IP Rating) is an industry-standard classification system that denotes the level of protection an item of equipment has against both solid and liquid particles, in accordance with BS EN 60529. The code is separated into two numbers, following the letters IP. For example, IP65. The larger the digit, the greater the level of protection.
Light Emitting Diode (LED)
A semiconductor that when energised emits blue light. LEDs usually incorporate a phosphor layer to change the colour characteristics to white light at various colour temperatures (CCT).
The amount of luminous flux (lumens) still being emitted at a given time (in hours) during the life of LEDs. This varies between different type and quality of LEDs and the characteristics of the luminaire, particularly the temperature at which the LEDs are operated. Expressed as L and B percentages at a specific number of running hours. E.g. L80B50 50,000 hrs means that after 50,000 hours of operation the LEDs are on average emitting 80% of their initial lumens (L80), of which 50% of LEDs are emitting less than 80% (B50).
Lumen/ Watts (lm/W)
Lumen/ Watt is a ratio expressing the luminous efficacy of a light source. The symbol used for lumen/ watt is Lm/w.
A lumen is the unit of luminous flux which expresses the total light emitted by a light source. The symbol for lumens is lm.
The unit of surface brightness of an object, expressed in candelas/m² (cd/m²).
The SI (International) unit of illuminance or light falling onto a surface. One lux is equal to one lumen per square meter.
PC – Polycarbonate
Strong diffuser polymer used outdoors and indoors. Good resistance to yellowing and high fire-rated and impact-resistant properties. Medium-light transmission when used in diffusers.
PMMA – Acrylic
PMMA/ Acrylic is a popular diffuser material due to high light transmission and UV stable for anti-yellowing. Very good optical properties.
The ratio of working (true) power (W) to the total (apparent) power (VA), measuring efficiency in an AC power system.
PP – Polypropylene
Low-cost material. Medium-light transmission and tough. Stability agents can be added to improve resistance to yellowing.
PS – Polystyrene
Polystyrene is an economical material, very popular for diffusers due to rigidity and good to high light transmission. Suitable for indoor use only. Stability agents can be added to improve resistance to yellowing. Molecular structure can be modified to achieve TP(a) and TP(b) ratings.
Luminaire mounted into the ceiling or wall or other surface so that any visible projection is insignificant.
Speed of Light
The speed of light is approximately 186,000 miles per second.
Thermoplastic Diffusers TP(a) and TP(b)
The type and rating of plastic diffusers used in luminaires, for compliance with The Building Regulations 2010 Fire Safety Approved Document B, Volume 2: Buildings other than Dwelling Houses. Only applies to recessed fittings, where the diffuser forms part of the ceiling. Diffusers are rated TP(a) or TP(b) according to their ability to restrict the spread of flames/fire. TP(a) - Self-extinguishing. No restrictions on their use, except in protected zones. TP(b) - Restrict the spread of flame. Total surface area of diffuser cannot exceed 15% in circulation areas and cannot be closer than 3m edge to edge. In open areas, surface area of diffusers cannot exceed 50% and spacing cannot be less than the largest plan dimension of the largest diffuser. Neither can be used in protected stairways or zones. Variations apply between UK nations.
UGR (Unified Glare Rating)
UGR is a method of defining the level of discomfort glare for any interior lighting application. UGR values can range from 13 to 30, with less glare likely the lower the number is. UGR 19 is the advised maximum value for offices. Lighting design software can be used to accurately calculate UGR at chosen, specific 'observer' points. UGR tables are also available for specific luminaires based on typical room sizes and can give an initial indication of whether a product is likely to be suitable for an installation.
The unit for measuring electrical power.