The single parameter that dictates the brightness of a light source perceived by an eye is

Step-by-step solution

The brightness of a light source perceived by the human eye depends not only on the total energy emitted per second (radiant flux) but also on the sensitivity of the eye to the wavelengths of the emitted light. Luminous flux is the measure of the perceived power of light, which is obtained by weighting the radiant flux according to the luminosity function (the human eye's sensitivity to different wavelengths). Therefore, the single parameter that dictates the perceived brightness is the total luminous flux entering