A method for calculating two indexes that involves both luminous efficacy of radiation (LER) and colour quality (CQ) is presented. The generic name of these new indexes is Efficacy and Colour Quality (ECQ) and they are designed to classify groups of light sources in a ranking by analysing several of their spectrum features. With this calculation the optimal CQ/LER tradeoff can be defined through the value given to a coefficient representing the weight that colour quality should have in the ranking established. Using a linear combination between