Resolving UV photometer outputs with modeled intensity profiles

Abstract

Photometers are usually reliable indicators of UV intensities in collimated (parallel light source) beams. However, they are not reliable for measuring UV intensity profiles in close proximity to a line source. This is due to both the geometry of line source emissions and to the variable response of photometers within a nonparallel light field. Empirical correction factors for the response of a hand-held radiometer were incorporated into the sum of point source lamp model to obtain a rational estimate of the intensity profile in close proximity (1–3 cm) to a 15.7 cm long UV source. The correction factors included (1) a physical offset because the face of the photosensitive cell is further from the lamp than the face of the detector, (2) an angle specific sensitivity function, (3) reflection at interfering surfaces, and (4) a mathematical simulation for the difference between the recovery of spherical versus planar light. A series of light profiles were recorded in close proximity to the lamp and compared to the uncorrected sum of point source model, and a model simulating the photometer with the empirical corrections noted above. The meter model was calibrated at one of the points by adjusting the modeled wattage of the lamp. The meter model gave a reasonable result compared to the meter reading at all other points. In this way, the rational intensity, defined as the expected intensity predicted by the sum of point source model without correction was found. At the surface of the lamp, the rational intensity was found to be 4× as great as the measured or meter model result.