Light Distribution by LumberingTroll
So I wanted to learn the relative distances for each light in the game so I built a series of stalls and put markers on the back wall, each stall is 60m high and there is a marker line every 5m. The test was performed on Alioth, at night (there is a lot of ambient light no matter where you are, sadly.
Vertical Lights XS, S, M, L
Long Lights XS, S, M, L
Square Lights XS, S, M, L
As you can see they have different lighting properties based on type and size, the Vertical lights have by far the longest attenuation but are also the brightest so tend to wash things out a bit. The long lights are great for smaller enclosed spaces providing a good balance between brightness and attenuation. The square lights are the middle ground, brighter than the longs, but have better attenuation as well. Personally, I love using Square L for my large factory areas, as long as they are not more than roughly 60m above the floor they provide good coverage.
Note: The Long XS and Square XS are bugged, they do not actually cast any light at all, the texture on the light is luminescent and casts a reflection but does not actually cast any light value as you can see in this picture, I tested it extensively even at ranges of less than 25cm.
I did this for my own knowledge and figured I'd share, enjoy and I hope you find it useful.
Bonus Resource and Material processing floor of my factory, built on an L core, using 9 Square Light Ls