<p>Lighting is routinely specified only by its impact on the three cone photoreceptors via the correlated color temperature (CCT), ignoring the visual and non-visual contributions of the melanopsin photoreceptors. Disentangling the behavioral effects of the CCT from those of the&#xa0;melanopsin excitation is complex but necessary to understand melanopsin’s effects and to inform the design of new lighting spectra for the built environment. Melanopsin photoreception is important for driving many visual and non-visual functions in humans, including circadian rhythms, mood, attention, and arousal. Here, we introduce a methodology using a widely available LED source (Philips Hue Play, Signify N.V.) to decouple the effects of melanopsin from those of cone photoreceptors. We present a computational algorithm for producing two ambient illuminations with different melanopsin and rhodopsin activation levels, whilst maintaining the same cone excitations, CCT and visual appearance (i.e., the two lighting conditions are cone metamers); this simple and inexpensive method removes the major confounding factor present in approaches that alter the melanopsin excitation of a light by exchanging the wavelength, color, or CCT. The method may find applications in behavioral experiments, including for clinical trials.</p>