During fabrication, LEDs grow in the form of a crystal wafer. A 2-inch diameter wafer can carry more than 20,000 LED chips. Colour and intensity variations are common across a wafer. LED suppliers can supply LEDs “binned” into various groups by wavelength, luminous flux, voltage drops, and other characteristics. E.g. Select LED’s from a particular colour bin to minimise visual colour differences between an array of different LED’s.
Black Body Radiation
All matter emits electromagnetic radiation when it has a temperature above absolute zero. A perfect black body is in thermal equilibrium with its surroundings. A black-body at room temperature appears black, as most of the energy it radiates is infra-red and cannot be seen by the human eye. At higher temperatures, black bodies glow with increasing brightness and colours that range from dull red to blindingly brilliant blue-white as the temperature increases.
CAD (Computer Aided Design)
An abbreviation used to describe the creation of models to represent 3D objects and their associated drawings. See IGES and STEP file formats.
The SI base unit of luminous intensity which is the power emitted by a light source in a particular direction, weighted by the sensitivity of the human eye.
An optical system that uses both reflection and refraction of light. E.g. Carclo’s 60mm optic combines a reflective surface with refracting elements to produce an extremely compact and ultra-narrow beam.
CCT (Correlated Colour Temperature)
The temperature of the black-body radiator whose perceived colour most closely resembles that of a given stimulus at the same brightness and under specified viewing conditions.
CIE Chromaticity Diagram
In 1931 (Commission Internationale de l’Eclairage (CIE) established the X-Y-Z tristimulus system for measuring colour properties, based on the assumption that every colour is a combination of three primary colors: red, green and blue. The CIE Chromaticity Diagram is a two dimensional colour space that defines all of the colours perceived by the human eye. Pure colours are located on the extreme outer edges of the diagram and white is located near the centre.
CRI (Colour Rendering Index)
A number on a scale 0-100 that represents the ability of an artificial light source to reproduce how the colours in an object look compared to an ideal light source, e.g. day light CRI = 100. The higher the CRI the more realistic it is.
Dominant Wavelength (λd)
A measure of the hue sensation perceived by the human eye.
Efficacy is a quantity often used to describe how efficiently a light fixture (or even an LED) is producing light. It is simply the ratio of how much light you get out compared to how much electrical power you put in. Hence, it uses units of lumens per Watt (i.e. lm/W).