Caption: The psychophysical sensitivity of the average human eye (i.e., the luminosity function).

The vertical scale is just relative to maximum sensitivity set to 100 %.

The colored vertical lines are at the wavelengths of some common laser colors. The yellow line is the unresolved atomic spectral lines the doublet sodium (Na) D lines (588.995 nm, 588.995 nm).

This luminosity function is for photopic vision (i.e., human eye vision under well lit conditions).

There is another luminosity function for scotopic vision (i.e., human eye vision under poorly lit conditions).

Credit/Permission: User:Skatebiker, 2010 / Public domain.
Image link: Wikipedia: File:Eyesensitivity.png.
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