All, I'm looking for a little hypothesis help here. I know that most detergents these days contain optical brighteners--they absorb UV and re-emit visible light the blue violet region. I noticed, though, that looking at my laundry detergent under a CFL bulb produces this rather neat violet line at the top of the detergent. So, I'm wondering why this is the case. Holding the detergent in front of a sunny window does not produce the violet line, but turning on a CFL above the sunny window does. I haven't been able to see if the line is produced by LEDs or incandescent bulbs yet. My guess is that CFLs could not possibly be emitting enough UV to cause this to fluoresce at the top, but CFLs must emit light at wavelengths that the optical brighteners are absorbing and re-emitting...so there must be some overlap between the UV and visible range that the optical brighteners can absorb. Thoughts?