Chromaticity means the property of a colour stimulus defined by its chromaticity coordinates (x and y).

Colour Rendering Index or CRI for short:
a) Means a metric quantifying the effect of an illuminant on the colour appearance of objects by comparison with their colour appearance under the reference illuminant as defined in standards produced by an international standardising body(9)
b) Is the average Ra of the colour rendering for the first 8 test colours (R1-R8) defined in standards produced by an international standardising body

Fluorescence means a phenomenon where light is produced by a gas discharge of the low-pressure mercury type in which most of the light is emitted by one or more layers of phosphors excited by the ultraviolet radiation from the discharge.

Fluorescent Light Source or FL for short means a light source which uses fluorescence as its lighting technology. It may have one (“single-capped”) or two (“double-capped”) connections (“caps”) to their electricity supply and it includes magnetic induction light sources.

Gas Discharge means a phenomenon where light is produced, directly or indirectly, by an electric discharge through a gas, plasma, metal vapour or a mixture of gases and vapours.

Halogen Light Source means an incandescent light source with a threadlike conductor made from tungsten surrounded by gas containing halogens or halogen compounds.

HID Light sources means the following types of light source:

High Pressure Sodium Light Source or HPS for short means a high intensity discharge light source:
a) In which the light is produced mainly by radiation from sodium vapour operating at a partial pressure of the order of 10 kilopascals.
b) With one (“single-ended’”) or two (“double-ended”) connectors to its electricity supply.

Incandescence means the phenomenon where light is produced from heat, and in light sources is typically produced through a threadlike conductor (“filament”) which is heated by the passage of an electric current.

LED refers to inorganic light-emitting diodes, and means a technology in which:
a) Light is produced from a solid state device embodying a p-n junction of inorganic material.
b) The junction emits optical radiation when excited by an electric current.

Light means electromagnetic radiation with a wavelength between 380 nm and 780 nm.

Mains or Mains Voltage (MV) means the electricity supply of 230 (± 10%) volt of alternating current at 50 Hz.

Average Luminance also known as Luminance-HLLS for a LED light source means the average of the luminance over a light-emitting area where the luminance is more than 50% of the peak luminance (cd/mm2).

Colour Consistency means the maximum deviation of the initial, spatially averaged chromaticity coordinates (x and y) of a single light source from the chromaticity centre point (cx and cy) declared by the manufacturer or the importer, expressed as the size (in steps) of the MacAdam ellipse formed around the chromaticity centre point (cx and cy).

Correlated Colour Temperature or CCT (K) for short means the temperature of a Planckian (black body) radiator whose perceived colour most closely resembles that of a given stimulus at the same brightness and under specified viewing conditions.

Directional Light Source or DLS for short means a light source which has at least 80% of total luminous flux within a solid angle of π sr (corresponding to a cone with angle of 120°).

G4, GY6.35 and G9 means an electrical interface of a light source consisting of two small pins at distances of 4, 6.35 and 9 mm respectively, as defined in standards produced by an international standardising body.

Lifetime or L70B50 lifetime for LED and OLED light sources means the time in hours between the start of their use and the moment when for 50% of a population of light sources the light output has gradually degraded to a value below 70% of the initial luminous flux.

Lumen Maintenance Factor also known as XLMF means the ratio of the luminous flux emitted by a light source at a given time in its life to the initial luminous flux.

Luminance (in a given direction, at a given point of a real or imaginary surface) means the luminous flux transmitted by an elementary beam passing through the given point and propagating in the solid angle containing the given direction divided by the area of a section of that beam containing the given point (cd/m2).

Luminous Intensity (candela or cd) means the quotient of the luminous flux leaving the source and propagated in the element of solid angle containing a given direction, by the element of solid angle.

Magnetic Induction Light Source means a light source using fluorescent technology, where energy is transferred to the gas discharge by means of an induced high-frequency magnetic field.

Mains Light Source or MLS for short means a light source that can be operated directly on the mains electricity supply, and includes light sources that operate directly on the mains but can also operate indirectly on the mains using a separate control gear.

Non-Directional Light Source or NDLS for short means a light source that is not a directional light source.

Useful Luminous Flux also known as Φuse means the part of the luminous flux of a light source that is considered when determining its energy efficiency, and is:
a) For non-directional light sources, the total flux emitted in a solid angle of 4π sr (corresponding to a 360° sphere).
b) For directional light sources with beam angle ≥ 90°, the flux emitted in a solid angle of π sr (corresponding to a cone with angle of 120°).
c) For directional light sources with beam angle < 90°, the flux emitted in a solid angle of 0.586 π sr (corresponding to a cone with angle of 90°).