...to make a video for an electronic engineer friend of mine. He
reckons they would work as a thermal imager and I don't.

Has been discussed at least once here before...

http://groups.google.com/group/sci.e..._thread/thread
/c131d84daf4fb7d6/8805419d6ac22d53?q=group%3A*electronics*&lnk=ol&