I didn't use red glass, I simply used red tail light repair tape found at automotive stores. I tried one layer first and the light still appeared almost white, so I went with two layers and the light appeared sort of light violet, then I tried 3 layers and that did it. Did going from white to red bring down the intensity of the white light? Yes, but not so much to make it useless, it's the brightest tail light I have and the brightest I've seen where I live. The only tail lights I've seen that were more noticeable were a couple of cyclists I saw who had those large 5" x 4" rectangular shaped lights with a dozen or more LED's.

Those larger lights looked like this: http://www.ledsafetylights.com/safet...p?ProductID=85 While each LED is not near as bright as my one single LED, but the combined effort of 18 leds in a large area makes the light extremely noticeable and you can see it fast from very far away...like a car or motorcycle tail light. Those are probably the best bicycle tail light for noticebility you can get currently for a light, but few cyclist want such a large light on their bikes.