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P. A. Smith, T. K. Kuyk, J. R. Dykes, L. N. McLin, L. E. Barnes; Effects of Pulsed and Continuous Glare on Obstacle Avoidance. Invest. Ophthalmol. Vis. Sci. 2008;49(13):2540. doi: https://doi.org/.
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In some situations, pulsed or strobed light has been found to impair performance more than steady light. Furthermore, a flickering light at a frequency around 10 Hz can appear brighter than a steady light in a phenomenon known as brightness enhancement. The goal of this study was to determine if pulsed glare (PG) had a greater effect than continuous glare (CG) on human performance in an obstacle avoidance task that requires visual processing of moving stimuli. A second objective was to assess if there was any evidence of brightness enhancement.
The ability to avoid obstacles in a simulated driving task was assessed in eight subjects under twilight (3 cd·m-²) lighting conditions. The task was maneuvering through a slalom course of rows of warning cones at 10 and 25 mph under normal viewing or with different levels of glare present. The glare source was a 532 nm green laser centered in the display field of view and operated at corneal irradiances of 6, 19, 60, 190 and 600 µW·cm-². The laser was either on continuously or pulsed at 8 or 12 Hz with a .317 duty cycle to give average irradiances of 1.9, 6, 19, 60, and 190 µW·cm-². The dependent variable was the probability of hitting cones, with an adjustment made for accidentally going off road and around the cones.
Performance declined as glare intensity increased in both the PG and CG conditions, with the first significant increase in probability of cones hit occurring at 60 µW·cm-² and rising to 40 and 30%, respectively, at 600 µW·cm-². Additional analysis indicated there was no difference between the 8 and 12 Hz PG conditions, so the results were combined. When the two glare types were compared with respect to peak irradiance level, PG was about 50% less effective from 60 to 600 µW·cm-² than CG in reducing performance. However, when CG and PG were compared with respect to average irradiance, PG was about 50% more effective than the CG (F = 6.489; p = .038) in reducing performance.
Both CG and PG were effective in disrupting human performance in an obstacle avoidance task at irradiance levels of 60 µW·cm-² and above. The relative effectiveness of the two glare types depends on how they are compared with respect to irradiance. When compared with respect to average irradiance, the PG was more effective than CG. This suggests that brightness enhancement may have occurred.
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