I broke down and bought a VEML6075 UVA/B Sensor Breakout and a LTR-559 Light & Proximity Sensor Breakout. And one of the RV3028 Real-Time Clock (RTC) Breakout.
Only just in the testing phase, making sure they work.
I scored a couple of the glass strips you use for Microscope slides from my dogs veterinarian. Its fused quartz glass that will not block UV light. Its about as transparent as you can get. Two lengths side by side should do it. I’ll use RTV silicon to hold them in place. Apparently most plastics and glass block UV light.