Assessing Colour Differences of Lighting Stimuli Using a Visual Display

A large scale experiment was carried out to accumulate colour difference discrimination data for lighting stimuli which were simulated on a display. Twenty six colour centres were selected and twenty one pairs of chromaticity difference were prepared surrounding each colour centre. Each pair was assessed using ratio method against a grey and a black background by a group of 20 normal colour vision observers. Both white and coloured lighting stimuli were used; corresponding to specifications for the solid state white lighting products and part of the MacAdam colour centres respectively. The latter defined the fundamental research for visual sensitivities known as just noticeable difference (JND). The results were used to test colour spaces and chromaticity diagrams as well as to evaluate colour difference predictions of various colour difference formulae and colour appearance models. It was found that u'v' chromaticity diagram can represent colour discrimination data for lighting colour stimuli more uniformly. Moreover, CIELUV colour difference formula performed better in predicting colour differences for lighting stimuli; especially when using black background. It performed better than CIEDE2000 and CAM02-UCS formulae, which were derived based on surface colours, even though it has been shown in the previous studies that these perform well when simulating surface colours on display. These points also support that the experimental arrangement could potentially be used to simulate light sources (luminaires) in order to evaluate them as lighting stimuli. Furthermore, the visual results obtained against the black background can mostly be predicted better by the models than those against the grey background for lightning stimuli.