Photonics Cluster laboratories also perform scientific measurements of colour. Colorimetric measurements are taken with reference to the tristimulus theory of human vision. This theory states that the human retina has red, blue and green cones. The mixed response of these cones allows the eye to see colour and each type of cone has a colour matching function, known as X, Y and Z respectively. The CIE 1931 diagram uses the tristimulus theory to model colour response in two dimensions.

The advantage of the CIE 1931 diagram is that any colour can be represented by two chromaticity co-ordinates, x and y. The line on the diagram is known as the Planckian locus, and is the region where the different colours mix to produce white light. The position of any white light source on this line is defined by its colour temperature. Low temperatures represent a reddish, "warm" light, high temperatures represent a bluish, "cool" light. Colours that lie close to this line have a correlated colour temperature (CCT.)

The colour rendering index (CRI) defines how well colours are rendered by the measured source of illumination. This index is based on the average of eight standard colour tiles - the smaller the difference in perceived colour, the better the colour rendering. The higher the value of CRI, the closer the source approximates white light.

All three Photonics Cluster spectroradiometers can measure colorimetric quantities to an accuracy of better than 1%. The CL 200 also allows measurement of colorimetric units to a similar accuracy. As well as the hand held meters and the spectroradiometers, the laboratories also have a Radiant Imaging imaging photometric and colorimetric system. This system is a digital camera employing three filters, red, green and blue, enabling images to be taken and immediately analysed for their photometric and colorimetric data.

Mobile Phone Backlight

LCD Display

Bank of Red LEDs

OLEDs

Mobile Phone Key Pad

EXIT Sign