Listed below are some typical colour rendering groups of light sources:
| Light source | Colour rendering group |
|---|---|
| Incandescent | 1A |
| Metal halide | 1A ... 2 |
| Fluorescent | 1A ... 3 |
| High pressure sodium | 1B ... 4 |
| Low pressure sodium | 4 |
Colour rendering index for different light sources
The reason for lamps with a poor colour rendering such as high and low pressure sodium being used at all is their high efficacy. They output more light per Watts of electrical power than lamps that provide a good colour rendering. The luminous efficacy is given as the ratio of lamp lumens/lamp watts. It is generally true that lamps with high wattages are more efficient than their low-wattage counterparts.
Incandescent
Metal halide
Fluorescent
High Pressure
Sodium
(All images courtesy of Philips Lighting)