3 Colour Rendering Index (CRI)

The appearance of an object depends upon the available wavelengths of light that fall on that object, and some light sources illuminate objects more accurately than others.

This ability to accurately represent colours is called the Colour Rendering Index, or CRI, and is based on a scale from 0 to 100.

When comparing light sources, the sun was chosen as the reference source, and so would have a CRI equal to 100. However objects look while under the sun, that’s the true colour and appearance of that object.

Some artificial light sources have better CRI than others. For example, an incandescent lamp is considered an excellent source of white light, as it emits all wavelengths of visible light. In contrast, a Low Pressure Sodium (LPS) lamp is considered to have a very poor CRI rating, as it emits only a narrow band of wavelengths, causing objects illuminated by it to have a very dull yellow tone.

Light sources with a high CRI cause the least emphasis or distortion of colour and are desirable for areas where colour discrimination is important. All incandescent and white light LED lamps have very good CRI ratings.