The effect of surround luminance on measurements of contrast sensitivity

Abstract

We investigated how the luminance of an immediate surround to a visual target affects the measurement of contrast sensitivity. We examined four young, healthy, subjects under typical lighting conditions for each test but varied the surround luminance systematically by controlling a backlit surround. The effect of varying the surround on contrast sensitivity measurements made with a Pelli-Robson chart was minimal. The only statistically significant difference was between measurements made with a 900 cd.m-2 surround compared to those made with 5.6, 9, or 30 cd.m-2 surrounds when tested at a viewing distance of 4 m. The higher luminance surround produced higher levels of contrast sensitivity. The effect of the surround luminance was greater when measuring contrast sensitivity to sinewave gratings using a method of constant stimuli. Optimum performance was found using a surround luminance of 9 cd.m-2 (20% of the mean target luminance). Statistically, a wide range of surround luminances (3-30 cd.m-2, or 7-67% mean target luminance) gave similar levels of visual performance, but higher luminance surrounds led to reduced contrast sensitivity. Possible reasons for the difference in the effect of the surround depending upon the test are discussed. Ophthalmic practitioners using contrast sensitivity measurements with letter charts probably need not make special efforts to illuminate the test surround appropriately. However, practitioners using sinewave gratings, especially computer generated sinewave gratings, to measure contrast sensitivity, may have their measurements affected by inappropriately lit task surrounds.

The influence of spectral power distribution on contrast sensitivity

“…Second, some psychophysical experiments which analyse the influence of surround luminance on contrast sensitivity have been performed by changing the current through the lamps. 11,14 The results obtained in the present experiment confirm the validity of the conclusions obtained in these studies and supports this technique for future research work. Third, the CCT used in our experiment do not cover the range over which fluorescent lamps operate; however, the lighting obtained by dimming tungsten halogen lamps does have a correlated colour temperature similar to that of the low pressure sodium lamp.…”

“…These studies have employed a wide variety of light sources (tungsten halogen lamps, fluorescent lamps, or even LEDs) but there is little knowledge of the influence of the spectral power distribution (SPD) on the measured contrast sensitivity. In some of these studies 11,14 surround luminance is changed by varying the electrical current through the light source. This might create uncertainty about whether the influence of surround lighting on contrast sensitivity is due to luminance of the surround or to the SPD of light from the surround.…”

Portable LCD Image Quality: Effects of Surround Luminance

“…However, surround effects on the luminance CSF in spatial frequency domain appears to be less well investigated so far. Cox et al (Cox et al, 1999) measured the effect of surround luminance on CSF and visual acuity using computergenerated sinusoidal gratings under a surround levels up to 90 cd/m 2 for the purpose of ophthalmic practice in 1999. In consequence, reduced contrast sensitivity was measured under the highest surround luminance (90 cd/m 2 ) and the optimal surround level was found to be at 10 ~ 30% of mean luminance of a target stimulus.…”

Spatial Luminance Contrast Sensitivity: Effects of Surround

“…However, surround effects on the luminance CSF in the spatial frequency domain appears to be less well investigated thus far. Cox et al [30]. measured the effect of surround luminance on CSF and visual acuity using computer-generated sinusoidal gratings under surround levels up to 90 cd/m 2 for the purpose of ophthalmic practice in 1999.…”