I have an idea of what these glass filters may have been used for but, so as not to influence your thinking, I will mention those ideas later. Also, someone may know exactly what they are. The red filter lets absolutely no light,
emitted from a blue LED, to pass through it. I may use the red pass filter on a thermal imaging project that I have in the works. I have had these filters for so long that I have only hunches as to where I found them. I did the calcs with the numbers painted on the end but I remember that they seemed not quite right to be the frequency one would guess them to be.

