How does the human eye perceive light? What would happen if humans only had rod-type receptors?


What will be the ideal response?


ANSWER: We perceive light because radiant energy from the Sun travels outward in the form of electromagnetic waves. When these waves reach the human eye, they stimulate antenna-like nerve endings in the retina. These antennae are of two types—rods and cones. The rods respond to all wavelengths of visible light and give us the ability to distinguish light from dark. If people possessed rod-type receptors only, then only black and white vision would be possible. The cones respond to specific wavelengths of visible light. Radiation with a wavelength between 0.4 and 0.7 micrometers (µm) strikes the cones, which immediately fire an impulse through the nervous system to the brain, and we perceive this impulse as the sensation of color. (Color blindness is caused by missing or malfunctioning cones.) Wavelengths of radiation shorter than 0.4 µm, or longer than 0.7 µm, do not stimulate color vision in humans.


Right on time. Thanks a bunch.