Entoptic halos . If someone looks at a bright outdoor lamp in otherwise dark sur

Question

Entoptic halos. If someone looks at a bright outdoor lamp in otherwise dark surroundings, the lamp appears to be surrounded by bright and dark rings (hence halos) that are actually a circular diffraction pattern as in the figure, with the central maximum overlapping the direct light from the lamp. The diffraction is produced by structures within the cornea or lens of the eye (hence entoptic). If the lamp is monochromatic at wavelength 641 nm and the first dark ring subtends angular diameter 2.0° in the observer's view, what is the (linear) diameter of the structure producing the diffraction?

Explanation / Answer

The angular resolution is

            sin (theta) = 1.22 (lamda) / D

Diameter

              D = 1.22 ( 641 nm ) / sin 2.0

                  =22.407 micr0 meters

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