do you use a band reject (“notch”) filter?

I feared this. Toluene is similar to benzene, so it will fluoresce in the 220nm range. Once you get

into conjugated heterocycles like indole derivatives, the wavelength of max absorbance increases beyond 285nm.

it seems that anything that would fluoresce under a blacklight (365nm) would flood our CCD sensors. I think a 632nm module

would work, and they’re relatively cheap.