contrast l line l background l line l background u2062 number u2062 u2062 of u2062 u2062 egdes u2062 length length end u2062 u2062 effect the flicker contrast utilizes the common metric of contrast the ratio of intensities to achieve qualitatively the same result while being simpler to compute and avoiding singularities at low background or line intensity values referring to fig5 the flicker contrast 50 vertical axis exhibits the same invariance as a function of line length 52 horizontal axis and number of lines per pattern as is exhibited by the flicker energy the end effect term of the flicker energy and flicker contrast equations compensates for the spatial summation performed by the eye 39 s retinal system in integrating the effect of edges line ends when the visual field representing the line extends laterally to involve multiple visual receptors end effect values were determined by the nonlinear least squares best fit to the test data which yielded the smallest variation in the resulting flicker energy for all combinations of line numbers and lengths at a particular background luminance and viewing distance exemplary values of the end effect for lines brighter than the background and lines darker than the background at different levels of background luminance are end effect number of pixels background luminance cd m 2 48 96 154 192 brighter lines darker background 8 9 6 3 5 0 4 3 darker lines brighter background 44 8 16 1 9 2 6 3 however the fit to the test data is not strongly dependent on the exact value of the end effect parameter and an.