Luminous energy Q v is related to radiant energy Q e by the expression Q v = 683.002 l m / W ⋅ ⋅ ∫ ∫ 0 ∞ ∞ Q e ( λ λ ) y ¯ ¯ ( λ λ ) d λ λ . Here λ λ is the wavelength of light, and y ¯ ¯ ( λ λ ) is the luminous efficiency function, which represents the eye's sensitivity to different wavelengths of light.