A simple view is not possible to distinguish between a CR-39 and a polycarbonate, as are materials with very similar characteristics in terms of weight, ease of scoring (which is why they are usually sold with hard or scratch-resistant treatment ) and the two materials are impact resistant lens compared to the mineral. Mineral lens if you can differentiate simply by the sound when hit gently with something metal, but between polycarbonate and CR-39 sound is very similar.
So when I recommend you some glasses: if the frame (or frame) is complete, either metal or pasta (acetate) Become the CR-39 lenses that will not give you problems. On the contrary, if the frame is in the air (drilled) or nylor (or nylon, in which case the lens slot) requests polycarbonate lenses because it is more durable, but make sure that if you break it will cover the warranty. In most of the optics, if you will cover polycarbonate and avoid put CR-39 can be more easily from these types of frames. Another option instead of polycarbonate is to use a high-index organic lenses, which are also suitable for air or slotted frames, and its price and polycarbonate are very similar.
With the theme of UV passes as well, is a clear filter and therefore can not be seen with the naked eye, but at least here in Spain, the vast majority of lenses that are sold have the UV filter. Organic lenses depending on the material cut between 350 and 400 nm. and minerals around 330 nm. so the organisms have a greater protection.
With the theme of what we glare easier, because if you can easily check. By observing the reflection of a lens with the treatment we will see that the lens has a residual reflection color, here in Spain, are usually green, but depending on the house that marketed the lenses can be blue or pink. There is currently a treatment that leaves no residual reflection. But if we observe a non-glare lens we see that the reflections are white and very strong.
