08/05/2017

How to assess colours effectively using a light booth

Choosing a colour is a process which goes well beyond simply assessing a sample with a specific device. This is because a spectrophotometer tells us if a colour is correct from a colorimetric perspective and if it falls within acceptable variation levels but not necessarily if it is human vision appropriate.

To minimise client complaints (and there are a huge number of these in the colour world!!) visual assessment must be incorporated into quality control system using the well-known light booths.

Below I have set out eight simple steps for the creation of a quality protocol for colour assessments using light booths.

1. Knowing your own limits The first step is knowing your own limits! Unfortunately our visual apparatus (our eyes) is subject to imperfections due both to personal factors (see colour blindness to cite only the best known) and age (the retina tends to yellow with age). One of the most commonly used tests to judge our ability to recognise colours is the Farnsworth Munsell 100 hue test. This test is available on line. Just click here.
2. Choose the right light conditions It is important to choose the right light to observe and assess colours in. There is a reference lighting for each market, for example, the paint and varnish sectors uses D65 while graphics uses D50.
3. Position the sample correctly The overall rule is that samples must be seen in a 0°/45° geometry.  If you have two colours to compare ensure that the two samples come into lateral contact in such a way that perception of colour is not distorted in the central area.
4. Reduce light pollution The only source of light in the room should be that coming from the light booth when assessing colours. Any other sources of light can distort colour perception.
5. Reduce colour pollution The only source of colour in the light booth should be the colour being assessed and the standard. This is because other colour sources can modify our perception of the colour we are looking at.
6. Assessing potential metamerism Metamerism is a phenomenon which occurs when two colours look the same under one light but different under a second light. To assess whether metamerism is taking place, observe samples in a range of lights (light booths are usually equipped with lights such as D65, D50, A, TL84, UV).
7. Look quickly. Assessing a colour should not require more than 10 seconds. This is because eye focus varies over time. To assess a colour correctly look at it for a maximum of 10 seconds, rest your eyes and look once more.
8. Define standards It is important to define the standards with which any copies are to be examined. A colour card, production standard, a colour agreed with a client: these are all examples of standards. Standards enable us to ensure that our colour assessment procedures are top quality.