as a TF junkie and stained glass glazier I can point out glass would be too thick to fit on top the cardboard tube and it's pretty unlikely you'd get a piece cut a precise enough circle to glue inside the tube .... there is/was a thin plastic material in a variety of colors that use to be available, I think for sign makers, can't recall the name .... but I've found 'nothing' works fine, a white light there is as functional as green
Bill
