Mesopic vision covers roughly 0.005 to 5 cd/m squared, the range of roads, parking lots and outdoor areas at night. Rods and cones both contribute, and the eye's peak sensitivity slides toward blue as light falls, the Purkinje shift. Mesopic photometry adjusts lumens for this, crediting sources with higher S/P ratios with greater effective brightness for peripheral detection.
At 1 cd/m squared on that roadway we're well into mesopic, so the 4000 K retrofit buys some peripheral visibility.
Also heard as
- mesopic vision
- twilight vision
Related terms
Photopic
Describes daylight vision, when cones dominate, providing color and sharp detail at luminances above a few cd/m squared.
Scotopic
Describes night vision at very low light levels, when only rod cells respond and color disappears.
Luminance
The brightness of a surface or source as seen from a particular direction, measured in candelas per square meter.
V-lambda curve
The standard curve of the eye's daytime sensitivity to each wavelength, peaking in green at 555 nm.