Well, you might be gaining a bit of fresh cold air by not having a glass under your hood, but you are sending 'dirty' air out without being filtered. The glass is there to keep the heat inside the shade and the tubing is there to replace that air and remove the hot air generated by your bulb(s). The air going thru, is clean air and is never in touch with any that smells like bud. That glass pane is imperative if you don't want to smell up the neighborhood.

spaceneedle