The air
Haze dimming and reddening the lights.
Between a light and the eye the air takes some of its light: the molecules, far more of the blue than the red, and the haze, a little more of the blue.
- The molecules: Rayleigh scattering, 5.8, 13.6 and 33.1 per million metres at 680, 550 and 440 nm at sea level, thinning with the air's density.
- The haze: what the day's visibility leaves. Koschmieder's law gives the extinction at 550 nm as 3.912 over the visibility, the distance at which a black object's contrast falls to 2 %. What the molecules do not account for is the haze, carried to the other wavelengths with an Ångström exponent of 1.3.
A light at the visibility keeps 2 % of its green, and less of its blue: far lights redden. The beams' light in the air is that same scattering seen from the side. The haze scatters mostly forward, with an asymmetry of 0.7, and absorbs a tenth of what it meets.