Tech Thursday – Light Part 3 – Colour

January 17, 2013

This is the final instalment in our short three part series discussing Light.

  1. In the first part we will briefly looked at what we define light to be and went on to discuss some of the photometric units that are typically found in photometric measurements.
  2. In the second part we discussed Luminous Intensity and in particular how we go about measuring it in a meaningful way.
  3. In this final part we round-up the series with a brief introduction to colour, its measurement and the typical colour definitions used in signalling.


Definition and Measurement


Standard Colour Definitions & Meaning

Whilst we are unable to find a standard that directly defines the colour coding of warning beacons or visual alarm devices (VADs) we can borrow from the existing standard BS EN 60073 – “Basic and safety principles for man-machine interface, marking and identification – coding principles for indicators and actuators”

From this standard we shamelessly borrow the table:


Safety of persons or environment

Condition of process

State of equipment














Mandatory significance

White (Grey or Black)

No specific meaning assigned

This standard does not directly define what is meant by the individual colours in terms of chromaticity – for example what do we mean by red?  Instead it refers us to CIE publication No. 2-2 1975 – “Colours of light signals” which has now been superseded by standard CIE S 004/E-2001 – “Colours of light signals”.  Here may be found exact definitions of what constitutes Red, Yellow, Green, Blue and White light signals.


This is the final instalment of the three part series discussing various properties of light.  We very briefly looked at Colour and its measurement as well as how we can usefully apply colour to signalling situations in a uniform standardised manner.

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