The rule
Position lights to CS/FAR 25.1385 to 25.1397.
The position lights are drawn at what the rule asks of them, which is a
minimum: a real light gives at least as much, and scale says how many times
as much.
Over the arc
In the horizontal plane, the red and the green give 40 cd from dead ahead to 10° out, 30 cd to 20° and 5 cd on to 110°. The white gives 20 cd over the 140° astern (25.1391). Above and below, each gives a share of that: 90 % at 5°, half at 20°, a tenth at 40° and 5 % straight up or down (25.1393).
Past it
A light may not spill far into its neighbour's arc. The rule caps the red in
the green's arc at 10 cd, and in the white's at 5 cd, in a band out to 20°
past the edge, and at 1 cd beyond (25.1395). The light here falls from its
edge value to those caps geometrically, as a lamp's cut-off does. spill
scales the caps: 0 cuts a light off at its edge.
The colours
The rule bounds each colour in the CIE 1931 diagram (25.1397). The red and the green are LEDs' at 625 and 525 nm, from the CIE colour matching functions. The white is a filament's, taken as illuminant A. Each is carried to linear sRGB at a luminance of one; one out of gamut is brought in by adding white, which keeps its luminance.