Glossary

Luminous Flux : The unit of Luminous Flux is Lumen. The total light emitted in all the directions is measured for the light source in “LUMENS”.

Luminous Intensity : Luminous Intensity is a measure of Brightness. Candela per square centimeter is the unit of measurement. Candela is the luminous Intensity in the perpendicular direction of the surface of 1/600,000 square meter of a full radiator at the temperature of freezing Platinum. One Candela equals 0.982 International Candles.

Brightness : Brightness of a surface is that property by which the surface appears to emit more or less light in the direction of the view. This is subjective quantity. The corresponding physical measurement of the light actually emitted/reflected is called Luminance.

Luminance : Luminance of a surface is the measure of the light actually emitted per unit projected area surface. The luminance of a surface emitting or reflecting is measured in Candela per square centimeter.Illuminance of a surface is defined as the Luminous Flux reaching it perpendicularly per unit area. The British Unit is foot-candle (Lumen/Square foot). The Metric Unit is LUX (Lumen/Square meter).

Contrast : Contrast is an expression used in many different circumstances to explain dissimilarity either of brightness or of colour.

Lumen Depreciation : The amount of Luminous flux of a new lamp will slowly diminish as the lamp continues its operation through its life. The amount of reduction in luminous flux is called Lumen depreciation.

Colour Designation : It is customary to refer to the colour of the light from the sun thus the colour of the Twilight in Greenwich in Mid Summer is termed as Daylight (6000K). Similarly colour of the Twilight in Mid summer in the tropical region is called Tropical/Cool daylight (6500K). Warm white (3000K) and cool white (4000K) contain more of orange and red colour giving an impression of warmth.

Colour Temperature : When the standard BLACK BODY is raised to a temperature, it emits light by incandescence. The colour of the light so emitted, is expressed in terms of its temperature in degrees Kelvin.

Chromaticity: Chromaticity is a method of recognizing colours. Trichromatic (CIE) system of colour measurement is an International practice. All the lights spectrum are artificially selected and designated in XY coordinates to easily represent on the graph: CHROMATICITY DIAGRAM. Colour Temperature can also be represented as Black Body Temperature locus (Planckian curve) in the Chromaticity Diagram.

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