How is light translated by the eyes and brain into the sensation of visual stimulus?
Light exists as a wavelength of electromagnetic radiation. As such, it is not a tangible substance, but instead may or may not be both a wave and particle. Light is sensed and translated in the brain by the eyes, which utilize photoreceptor cells in the retina in a process called Transduction.
Transduction is the process of transforming a stimulus into another form. In the case of light, human eyes are receptive to a specific wavelength, which is reflected off every solid surface and received by the retina. The retina contains three types of photoreceptor cells, which absorb different wavelengths and translate those into visual stimuli; photons are absorbed, which triggers a chemical response, and finally an electrical response which can be read by the brain. The more abundant rod cells absorb dimmer light of many wavelengths, while cone cells absorb brighter lights and translate color. The third type of photoreceptor are the photosensitive ganglion cells, which help the eyes and brain adjust to cycles of light and dark. All three types absorb photons at different wavelengths to allow processing of all light in the visual range.