The perceived colour of a stimulus depends on the conditions under which it is viewed. For colours employed as an
important cue or identifier, such as signage and brand colours, colour reproduction tolerances are critically important.
Typically, such stimuli would be judged using a known level of illumination but, in the target environment, the level of
illumination used to view the samples may be entirely different. The effect of changes in the viewing condition on the
perceptibility and acceptability of small colour differences should be understood when such tolerances and associated
viewing conditions, are specified.
A series of psychophysical experiments was conducted to determine whether changes in illumination level significantly
alter acceptability and perceptibility thresholds of uniform colour stimuli. It was found that perceived colour
discrimination thresholds varied by up to 2.0 ΔE00. For the perceptual correlate of hue however, this value could be of
significance if the accepted error of colour difference was at the threshold, thereby yielding the possibility of rejection
with changes in illumination level. Lightness and chroma on the other hand, exhibited greater tolerance and were less
likely to be rejected with illuminance changes.