Lighting Knowledge Library

An approximate warm/cool appearance of nominally white light, expressed in kelvin. CCT does not specify color rendition, brightness, glare, flicker or spectrum.

A traditional index comparing object-color appearance under a test source with a reference. Useful, but not a complete description of color quality.

Luminous flux: the amount of visible light emitted by a source or luminaire.

Illuminance: luminous flux per unit area. One lux is one lumen per square metre.

The nominal angular spread of a luminaire’s main beam. Real distributions are not hard-edged cones.

Control of light output. The driver, control protocol, luminaire and installation must be compatible.

A supplemental color-rendering index for a saturated red sample. It can matter where red appearance is important, but it is not a stand-alone quality verdict.

IES measures for color rendition. Rf describes average fidelity; Rg describes average gamut area. Neither single value replaces the full product/application review.

A reference curve associated with chromaticities of Planckian radiators at different temperatures; CCT is described relative to this locus.

Distance from the Planckian locus in chromaticity space. Similar CCTs can have different tints; positive and negative values indicate opposite sides of the locus.

How a light source’s radiant energy is distributed across wavelengths. It affects color rendition and visual character.

Luminous intensity in a particular direction; useful for understanding directional light such as a spotlight.

Luminaire luminous flux divided by system power. Compare complete luminaire output and wattage, not just LED-chip figures.

A method for evaluating discomfort glare in indoor installations. It depends on room geometry, surfaces, observer positions and luminaire arrangement.

A measure of chromaticity consistency between nominally similar light sources. Lower variation can matter when several fixtures are visible together; it is not a universal mandatory threshold.

Changes in light output over time. Effects may be visible or camera-detectable; vague “flicker free” claims do not replace measured data.

A metric related to short-term flicker severity under defined measurement conditions. Applicable limits depend on jurisdiction and product scope.

A metric for stroboscopic effects from temporal light modulation under defined measurement conditions.

A standardized digital lighting-control ecosystem based on the IEC 62386 series. DALI-2 certification is distinct from a general DALI-compatible interface.

Digital formats describing luminaire light distribution. They support meaningful project calculations; the actual file should match the specified product and optic.

Lifetime declarations combine a stated lumen-maintenance level, operating time and a statistical population measure. “Hours” alone is incomplete.

An enclosure protection classification for ingress of solids and water. Check it against the actual installation environment.

A classification of mechanical impact resistance where fixtures may be struck.

A compatible system deliberately becomes warmer in CCT as light output is reduced; this differs from ordinary dimming.

A system that allows CCT to be adjusted across a range. Use it where adjustable scenes are part of the project brief.