Generator
A sample with two reflectance curves, and neither below one
The apparent reflectance of an optically brightened sample, measured under D65 and A. It exceeds 1 — the shaded band — which no reflector can do: more light leaves at these wavelengths than arrives at them, because the sample absorbs in the violet and re-emits in the blue. And the two curves differ, so the sample has no single reflectance to store. The effect drawn here is a floor: most of the excitation band lies below 380 nm, outside the range computed here.
Drawn at its defaults, in real light sources.
It reads 2 options and
no others: under, obs.
Called by 2 essays
the blast radius of changing it
What light is
Some paper is brighter than white
The reflectance model assumes light leaving at a wavelength arrived at that wavelength. A fluorescent sample breaks the assumption, has no reflectance curve at all, and is in almost every sheet of white paper sold.
What a scene doesA surface that is not a multiplication
Every argument here about what light does to a surface begins by multiplying two spectra together. A surface with a brightener in it takes light at one wavelength and returns it at another, so it is a full operator rather than a diagonal one — and it does not have a reflectance at all.