Cover reduce light?

[fdiddy]

Originally Posted by fkshiu

Were you using a lux meter or a PAR meter for your readings? Sanjay Joshi's test show a PAR reduction of around 10-20% with a pane of tempered glass that is used for DE MH bulbs.

I don't think tempered would be the best way to go with this anyways. Glass only prevents certain frequencies of light from passing through due to the refractive index. I think most panes of glass will let sufficient light through, less than 10% reduction I believe. Just my humble opinion - No back up evidence other than a few University Physics Courses.. which don't exactly cover PAR values and things of the sort.