A chromatic (cone-opponent) model, the CHC model, was developed to predict mesopic detection thresholds for light increments on a mesopic background. In the present work, the psycho-physical testing of the CHC model (and its equivalent photometric model) is shown. The experiment was carried out with quasi-monochromatic (QM) red and QM green light increment stimuli on an achromatic background, and also with the additive mixture of QM red and QM green, a so-called “two-peak” yellow light increment. The method of constant stimuli was used. Detection thresholds (p=0.5) were computed by probit analysis, in terms of threshold increment radiance values. Spectral sensitivity functions of mesopic increment detection thresholds were compared with those of perceived photopic brightness. The application to realistic lighting situations needs further experiments. The CHC model (or a similar model based on the same principle) is suggested to solve the problem of non-additivity in every visual task where a “multi-peak” luminous efficiency function shows the activity of cone opponent mechanisms.