Mechanical Equivalent of Light

the ratio of the radiation flux in the visible region of the spectrum to the luminous flux produced by this radiation. The concept of the mechanical equivalent of light is usually applied to monochromatic light and this equivalent is a function of the wavelength ; of the light; the inverse function—the ratio of the luminous flux to the radiant flux—is called the spectral luminous efficiency of the radiation (or the spectral sensitivity of the average eye, the lumen equivalent of the power, or the luminosity of the radiation). The mechanical equivalent of light has its minimum value (0.00147 watt/lumen) at ; = 555 nanometers (the spectral sensitivity of the eye is a maximum at this wavelength).