A relation between adaptation luminancc and visual acuity for the Landolt ring under the uniform background

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The purpose of this study is to investigate the visual acuity as a function of the adaptation luminance with in the range from 0.005 to 4,000 cd/m^2. A room with sufficiently wide background luminance illuminated diffusely is set up to provide a visual environment for acuity test. The test objects are Landolt rings with luminous contrast of 92% and with in the errors of size less than ±3% from the standard values. The observers are five male students with normal vision and they judge the break orientations of Landolt rings by guess. Visual experiments are carried out according to the standard method of the visual acuity test. Results obtained are as follows.(1) The approximate equation of the curve which shows the relation between the resolutionable visual angle θ and the adaptation luminance obtained by the method of least squares is θ=(0.3775(0.344+L^<1/4>)^4)/L(minutes), where L (cd/m^2) is the adaptation luminance.(2) This equation shows that the visual acuities are lower than those of Moon and Spencer over the whole range of adaptation luminance, and seems to be more practical and more suitable than that of their's.(3) As for the relation between the visual acuity and the orientation of the breaks, the visual acuities in the vertical and horizontal directions are a little higher than those in the oblique directions.
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