Someone from Viewfinders posted a video discussing the use of UV filters on the front of digital cameras and whether this was a valuable thing to do. Their conclusion was that, contrary to film, sensors from digital cameras are not sensitive to UV so there is no advantage to filtering out UV. They did feel strongly that UV filters provide a valuable safety measure to protect the front lens element from dust, scratches and other physical ailments. I have always used UV filters for that purpose, but it got me to thinking about such filters and whether they really reduce the UV or whether they could be a simple glass plate with no UV attenuation.
To investigate this, I performed a simple homey experiment. I have a black-light lamp that was made for inspection using fluorescent penetrants. The hand-held lamp has a filter that blocks any visible light and only UV is emitted. It is well known that certain fabrics, such as white cotton will fluoresce under UV. If you put a white handkerchief under the black-light, the fabric will glow with a very bright white. I know that you cannot see the UV, so the filter would be useless if trying to see attenuation of the UV. However, if the filter blocks UV, then it should block the fluorescence of the white cotton. I held several UV filters made by different manufacturers between the UV source and the handkerchief. In no case was the fluorescence reduced. My conclusion is that the filter only works for some remote wavelength, different from my lamp, or else they are essentially just plain glass.
I can think of another test I could do in the summer. I could tape some filters to my skin and sit in the sun for awhile. If the UV from the sun is responsible for sun tanning, then there may be some lighter circles in the area of sunburn. Maybe later.
