Re: could optical brightener be textile dyes?

Yes, an optical brightener could certainly be considered a dye if you 
consider what a dye is and does... A dye "stains" a material, and when 
light hits the surface of the material, certain wavelengths are absorbed 
by the dye and the rest of the wavelengths reflect (bounce off).  
Wavelengths that bounce off are the ones that reach our eyes and are 
detected (seen). An optical brightener is similar in a lot of ways: Its 
molecular structure is similar, and it will "stain" (stick to) certain 
materials.  An optical brightener is basically a fluorescent dye: Light 
hits the optical brightener, in turn causing it to generate its own 
wavelengths of light that are radiated outward (emitted).