MacAdam colour discrimination data have been the fundamental basis for the definition of just noticeable colour difference. Lighting stimuli and products are compared in regard to these ellipses data. The current study examines the validity of the MacAdam ellipses and investigates the best tool to evaluate colour difference of light stimuli. Pairs of chromaticity colour difference were processed with the aim to be simulated as light sources on a display and over 23000 assessments were accumulated by a group of 20 observers. Experiments were based on the ratio method and all pairs were examined against two different backgrounds; a black background and a grey background with the same specifications as the one employed in the MacAdam experiment. Different colour difference metrics and colour spaces were investigated in terms of ellipse fitting and colour difference performance.