A computed factor allows quantifying the efficiency of a light filter to stimulate a non-visual physiological effect which is responsive to light entering into a subject's eye. The efficiency factor is based on a spectral light transmittance of the filter over the wavelength visible range, on a spectral sensitivity profile of the non-visual physiological effect, and on a spectral distribution of the light which enters into the subject's eye without using the filter. Such efficiency factor is useful in particular for an ophthalmic element designed for stimulating a non-visual physiological effect which is based on melanopsin light-absorption.