Many substances fluoresce under UV light. Are there any which do so under IR or are the energy levels all wrong ? I think short wavelength UV is converted to longer wave- length visible light by the fluorescee and IR is longer than visible. Just wondering if there's some quirk of nature/ physics that would make it possible to use invisible flood- lighting -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads