where [V.sub.mes]([lambda]) is the mesopic luminous efficiency function under given conditions, M(m) is a normalizing function such that [V.sub.mes]([lambda]) attains a maximum value of 1, and m is a coefficient dependent on the
adaptation luminance and spectrum.
2 describes the degree of change from photopic to mesopic luminance for different
adaptation luminances. The range of the multiplier (above and below 1.0) corresponds to the magnitude of the effect of spectrum, increasing as
adaptation luminance decreases.
DGI is computed from a formula that was developed to account for the effects of source brightness, size, location relative to line of sight, and
adaptation luminance. Table 3 lists the mean subjective response to values from the DGI formula as measured in environments with windows.
In practice,
adaptation luminance is usually taken as the average luminance in the relevant viewpoint, but it is a gross simplification.
