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1. (WO1997016707) ULTRAVIOLET SENSING APPARATUS
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1. UV sensing apparatus comprising a housing which is substantially opaque to electromagnetic radiation, an aperture formed in the housing, a filter positioned within the housing at the internal mouth of the aperture, a fluorescent member positioned within the housing on that side of the filter remote from that adjacent to the aperture, and a light sensor positioned within the housing to receive light emitted by the fluorescent member, wherein the filter is such that it substantially removes visible light, the fluorescent member is such as to fluoresce when subjected to UV radiation, and the light sensor is positioned so that substantially none of any electromagnetic radiation entering the housing via the aperture impinges upon the light sensor.
2. UV sensing apparatus as claimed in claim l, wherein the internal geometry of the apparatus and the refractive indices of IR within the apparatus are such that IR is not reflected internally within the fluorescent member at angles which allow the IR to egress towards the light sensor.
3. UV sensing apparatus as claimed in claim l or claim 2, wherein the light sensor is shielded by an internal housing wall in such a manner that substantially none of any electromagnetic radiation entering the housing via the aperture impinges upon the light sensor.
4. UV sensing apparatus as claimed in any one of claims l to 3, wherein the aperture is sized so that electromagnetic radiation entering the sensing apparatus is insufficient to cause saturation of the fluorescent member, and so that the light sensor is not saturated by the light emitted by the fluorescent member.
5. UV sensing apparatus as claimed in any one of claims 1 to 4, wherein the aperture is circular and has a diameter lying within the range of from 0.25 mm to 3 mm.

6. UV sensing apparatus as claimed in claim 5, wherein the aperture has a diameter lying within the range of from 0.75 mm to 2 mm.
7. UV sensing apparatus as claimed in any one of claims l to 6, wherein the filter is made of a dark blue glass.
8. UV sensing apparatus as claimed in any one of claims 1 to 7, wherein the fluorescent member is an acrylic slab coated on one side with an organic dye which fluoresces when subjected to UV radiation.
9. UV sensing apparatus as claimed in claim 8 , wherein the coated side of the acrylic slab is that side adjacent to the filter.
10. UV sensing apparatus as claimed in any one of claims l to 7, wherein the fluorescent member is an acrylic slab which is doped with an organic dye which fluoresces when subjected to UV radiation.
11. UV sensing apparatus as claimed in any one of claims 8 to 10, wherein the organic dye is a phosphor.
12. UV sensing apparatus as claimed in any one of claims 8 to 11, wherein the dye is such as to emit light of a predetermined frequency when subjected to UV radiation.
13. UV sensing apparatus as claimed in claim 12, wherein the dye is such as to emit green light.
14. UV sensing apparatus as claimed in any one of claims l to 13, wherein the fluorescent member is such that the intensity of fluorescent light emitted is substantially linearly proportional to the intensity of UV radiation received.
15. UV sensing apparatus as claimed in any one of claims 1 to 14, wherein the light sensor is a light-dependent resistor.
16. UV sensing apparatus as claimed in claim 15, wherein the resistance of the light-dependent resistor varies linearly with the intensity of the received light. 17. UV sensing apparatus as claimed in claim 8, or in any one of claims 9 to 16 when appendant to claim 8, wherein the light sensor is positioned at an edge of the acrylic slab so that fluorescent light passes to the light sensor only by internal reflection within the slab.