<prompt> For detection of light, minimum amount of light quanta reaching retina should be:16-May54More than 500  <response>: Visual threshold is the minimum amount of light detected by retina. Threshold for a single rod is 1 quantum of light. To distinguish light from this discharge, at least 5-6 rods should be excited synchronously. Hence, about 5-6 quanta of light is the visual threshold for retina. For 5-6 rods to be excited, about 100 quanta of light should reach the eye cornea. Many of the quanta are absorbed, reflected, or refracted in the intervening ocular media. 