are <16 brightness increments noticeable?

My memory is kind of fuzzy, but I think I read somewhere that brightness levels that are in increments less than 16 units are indiscernible from one another in vanilla doom. Is this true? And if so, is it true in any other source ports?

It's true. In prboom-plus it's 8.

Yes, levels 128..143 will look the same, and 144..159, 160..175, and so forth.

Oscillating lights will use the actual value, so you get slightly different rates of oscillating by a 1 or 2 unit difference.

Some ports have 8 unit steps. It is possible that some OpenGL ports support the full range (depends on what formula they use for lighting, e.g. whether they use the COLORMAP lump).

I'm not entirely certain, but I think smaller increments will still fade between the fixed light levels at different distances, but I've never explicitly tested it in Choc/Cripsy Doom.

Urthar said:

I'm not entirely certain, but I think smaller increments will still fade between the fixed light levels at different distances

No, in vanilla 144 and 159 are rendered exactly the same (and so forth).

A small difference can be used to prevent visplane merging, which is useful around a railing texture to prevent glitches.