On Friday my first year class was doing a design lab on coils and magnets. One student wanted to drop a magnet though a coil and measure the velocity of the magnet with a light gate. To make the magnet fall straight he suggested using a transparent tube so set I about finding one for. I always used to use a rolled up piece of OHP transparency but now we have SMART boards in (almost) every room we don't use them anymore so the next best thing was a sheet of laminating film. On the way back from the administration building I noticed something strange about the film, light was coming out of its edges. I wanted to show the students my discovery but it wouldn't work under the classroom lights. It seems that the plastic is fluorescent giving out visible blue light when exposed to the UV radiation in the sunlight. Some of this light internally reflects along the sheet emerging at the edges. If it was simply light incident on the sheet internally reflecting then it should work in any light.