Ok thanks for the responses to my other question; I think I now have it. I have a follow up question – that is almost on the same topic (but not quite) The complete spectrum (arund 200nm to 380nm) of UV light is absorbed by some plastics?? Elections will be moved to a more energetic orbital when absorbing photons with the same frequency, any wavelengths with non similar frequency with be emitted (e.g. red flower) or transmitted (e.g. glass). Water doesn’t use this electron reflection/absorption as it “just happens” to have the same frequency in the hydrogen bond that will absorb a portion of the lower (red) end of the spectrum. This is all well and good UNTIL I got to thinking about something like a clear polycarbonate sheet. If absorption is due to specific frequency of electron vibration – how can a polycarbonate sheet (or most types of glass and lots of other “stuff” for the matter) absorb virtually all wavelengths between around 200nm to 380nm. (UV a,b and c) Surely there must be something else going on. How does a polycarbonate sheet (e.g. sunglass lens) absorb ALL ultraviolet light. It must be a different process as I don’t think there that many electron frequencies. I have looked on google for many days and there are many descriptions of the results but I can't find one that gives a complete (physics) reason. Thank you LoL – this all follows on a from a discussion my family were having regarding the colour of beer and as I kept digging deeper and deeper more question seem to appear. I hope you all don’t mind me asking such (what must be to you) simple questions.