Stiles–Crawford effect

The Stiles - Crawford effect of the first kind (SCE -I) describes the perceived difference in brightness when a light beam travels through the open pupil. The perception of brightness similar to a Gaussian curve, ie at the nasal and temporal edge of the pupil, the perception of brightness is weak and at the point of best vision ( near the pupil center ) the highest.

The curve is described as follows: visibility

Is the orientation factor of the pin, which describes whether the curve is flatter or steeper. Since on the retina three kinds of cones and this at different points, depending of different wavelengths, different values ​​are obtained. is the pupil center ( not to be confused with the point of best vision) and r describes the measurement point on the pupil at a distance from the pupil center. Visibility is obtained depending on the measurement point on the pupil of the pupil center and the incident wavelength.

The Stiles - Crawford effect of the second kind (SCE -II) describes an additional perceived color change when a monochromatic light beam moves away from the pupil center. This color shift was published in 1937 by Stiles. But there is a fundamental connection with the release of 1933, is today spoken by the Stiles - Crawford effect of the second kind. The current theory suggests that the effect disappears when monochromatic light with decreasing bandwidth.

Both effects occur during daylight vision. The reason lies in the fiber properties of the cones, which are mainly in the fovea centralis of the retina and are responsible for color vision. Light entering the edge of the pupil falls within an angle of approximately 10 ˚ on the fovea. Result, less light is coupled into the pins and it is assumed that light weaker, less bright, true.

The optical Stiles - Crawford effect ( SCE O ) does not describe the SCE on the retina, but it is re- reflected back from the retina of light measured outside the eye.