The specs of the eye

• The range of light intensities from 10^-6 cd/m² of the rod threshold to 10⁹ cd/m² of solar disc (where cd/m² represents candelas per square meter). In this range of light intensities, clare blue sky is at 10³ cd/m² and snow in sunlight is at 10^4.5 cd/m². This wide range of light intensity is mediated by pupil size, by different types of receptors (rods for scotopic vision and cones for photopic vision), and adaption of the cones, as discussed later.

• Visual field and Spatial resolution

  The visual field is as wide as 150 degrees. The angular size of the sun or moon is about 0.5 degrees.

  The acuity varies drastically from the fovea to the peripharal. A 20/20 vision can recognize a letter of about 0.08 degrees (4.8 minutes) from 20 feet away.