Fluorescent lamp + IR filter =?

A quick diversion from infrared photography to Infrared Luminescence (aka fluorescence). This can be used to reveal faded writing on old and damaged documents, and for other forensic things. I recently discovered a somewhat elderly but fascinating article by the legendary Andrew Davidhazy (of Rochester Institute of Technology in the States) explaining a do-it-yourself approach to this. Usually you need an expensive infrared-blocking filter over the broad-spectrum/white light source and an infrared-pass filter over the lens. Also usually, if you try and take an infrared photo under fluorescent lights you get almost nothing but noise.

Andrew points out in this paper that the average fluorescent light bulb (which presumably includes a lot of those low energy bulbs now prevalent) has a strange spectrum, attuned to our vision, which includes (virtually) no infrared. So if you illuminate your document with this and have an infrared-pass filter over your camera lens, all that will get through is infrared resulting from fluorescence in the document. The light, which includes no infrared, causes some of the document to fluoresce at a longer wavelength and some of that gets through the infrared filter.

Something to try I think.