"I noticed (this could be my imagination) better growth and more trichome development under the light with no glass."

This is not your imagination. I've had to prove this many times to people by using any simple light meter. Fixed bulb, fixed meter, piece of optical glass from an expensive flat bed scanner. Got the light placed where the meter read 1000. Put the glass in right against the bulb, dropped to about 900. Moved the glass down by three inches, 500.

Glass reflects, after all.