glass in solar applications cuts 10% , plastic only 5-8%,
leaded/insulated glass even worse, even though no one would ever use that for a light.
of course scratched plastic diffuses the light all over the place, and makes it worse for flashlight, but it is interesting to point out that plastic has less overall light reduction. (i tested it its true)
i THINK that the reason glass is the 10% is because of its first reflective surface, the light hits a reflection and bouces back into the light, wheras plastic is less reflective. but it could have to do with density of the particals that incurr adsorption.
the more adsorption, and the more reflective surfaces, the more light is lossed, so that is how an plastic optics ONLY with no front lens is effective (untill it gets scratched). Then if they would stop the reflection between the led and the optics, by integrating the optic INTO the led, instead of having many surfaces, one less reflection would exist. i have tested melding a dome and optic as a single optical device, it didnt work (yet).
the UCL glass seems to pass more light through without as much reflecting back, must be coated? but UCL breaks VERY easily. it breaks so easily , that if you choose that method, you should have spares.
other glass types are high temperature, can handle high temp incan bulbs.
the perfect would be a glass that is ultraclear or coated against internal reflections, and still was durable. UCL is cool stuff, if it wouldnt break.
there is also Ruby glass, it is still a silicate based , which has optical properties which make it great for binoculars, and monoculars, either a metal coating , or stuff IN the glass which changes it properties. something like that, but i ignored it for monacles and flashlights because it filters more light. and it really doesnt seem to help with the reflection either. i donno, but that is another glass type that is used with flashlights.
