The relationship between distance in ultra-violet short wave(UVC) lamp and intensity of illumination

This experiment showed that decrease in the extent of UVC illumination is more evident than that of UVA inllumination when the UVC light distance was lengthened. The smaller the radiant area of UVC light duct, the more evident the in the extent of UVC illumination. The smaller the light distance, the bigger the decrease in proportion to UVC illumination.
When the light distance is larger than the diameter of UVC light duct, the intensity falls off a little. The results of this experiment are of definite with respect to clinical treatment, especially in body-cavity treatment with quartz club.