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F. T. Collison, M. Huynh, S. Kelly; The Effect of Pupil Size on Perceived Brightness With Yellow Tinted Lenses. Invest. Ophthalmol. Vis. Sci. 2010;51(13):1816.
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Yellow tinted lenses (YTLs) have been shown to increase brightness perception under certain conditions (Kelly, 1990; Wolffsohn, et al., 2000). It has been proposed that some of the increase in brightness perception is related to differences in pupil sizes (Chung and Pease, 1999). Pupil constriction is preferentially stimulated by short wavelength light and is greater when subjects view an achromatic field through neutral density filters (NDFs) than with luminance-matched YTLs (Chung and Pease, 1999). The purpose of our study was to measure brightness perception through YTLs and luminance matched achromatic filters under two conditions: one in which the pupil was free to vary and the other where the maximum pupil diameter was fixed at 3 mm.
Fourteen visually normal observers estimated the brightness of 6 circular achromatic targets ranging in luminance from 1 to 60 cd/m2 projected by a ceiling mounted digital projector. Using a magnitude estimation method, each subject was asked to assign a number to the brightness of the target. The targets were shown for 5 seconds with an inter-stimulus interval of 15 seconds. The 6 targets were presented twice in pseudo-random order for each trial.Two conditions were investigated. In the first condition, the subject’s pupil was allowed to freely constrict in response to the targets. In the other condition, the subject viewed the targets through an artificial 3 mm pupil, simulating a fixed-pupil situation. The subjects made brightness estimates while viewing the targets through either a yellow-orange filter (Wratten #16) or through luminance-matched NDFs.
Brightness perception was statistically greater when subjects viewed the targets with a full pupil versus through a 3 mm artificial pupil. This result was observed with both the NDF (F=6.779, p=0.022) and the YTL (F=5.6, p=0.034) conditions. However, brightness perceptions obtained with the NDFs did not significantly differ from those obtained with the YTLs.
The basic assumption underlying our experiment was substantiated in that pupillary diameter does significantly affect brightness perception. However, we did not demonstrate a brightness enhancement effect from the YTLs. This may be due to the use of a YTL with a higher cut-off wavelength compared with the YTLs used in previous studies that demonstrated a brightness enhancement effect.
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