CIE 107-1994

This Technical Report reviews the CIE international recommendations for the colours of signal lights. The CIE recommendations for signal colours were first adopted in 1951 and were revised in 1975. They have not since been subject to critical review in the light of new experimental evidence and changed technology. Published and unpublished reports of experiments on the recognition of signal colours were compiled and analysed. The data from those reports were brought on to a common base for dim signals, moderately bright signals and bright signals under conditions simulating both night and day observation. Some of the experiments included subjects with defective colour vision. Consideration of the data by the Committee and its expert advisors has lead to a number of recommendations for changes to the internationally accepted colour domains for signal colours, notably:

1. Restriction of the yellow boundary of red, abandonment of the restricted purple boundary of red and re-definition of the recommended red in signal systems used by persons with defective colour vision;
2. Substantial re-definition of the colour domain for yellow including the definition of special domains for yellow signals of high and low illuminance;
3. Restriction of the boundaries of the colour domain for green;
4. Amendment of the colour domain for white including the definition of a preferred domain and a secondary domain that can be used when there is little chance of confusion with white lights;
5. Restricting the green and white boundaries of blue to enhance recognition as well as defining a more desaturated blue that can be used when there is little chance of confusion with white and a special domain to be used for low illuminance blue signals;
6. Recommending the abandonment of violet as a signal colour.

Based on this report CIE will publish an International Standard on "Colours of Signal Lights". The publication contains 42 pages, 14 figures and 6 tables.