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Light sensitivity or photosensitivity refers to a notable or increased reactivity to light. Apart from vision , human beings have many physiological and psychological responses to light. In rare individuals an atypical response may result in serious discomfort, disease, or injury.
Photosensitivity is the amount to which an object reacts upon receiving photons, especially visible light.In medicine, the term is principally used for abnormal reactions of the skin, and two types are distinguished, photoallergy and phototoxicity.
This means that the brightest and the darkest light signal that the eye can sense are a factor of roughly 1,000,000,000 apart. However, in any given moment of time, the eye can only sense a contrast ratio of 1,000. What enables the wider reach is that the eye adapts its definition of what is black.
Photophobia is a medical symptom of abnormal intolerance to visual perception of light. [1] As a medical symptom, photophobia is not a morbid fear or phobia, but an experience of discomfort or pain to the eyes due to light exposure or by presence of actual physical sensitivity of the eyes, [2] though the term is sometimes additionally applied to abnormal or irrational fear of light, such as ...
A rod cell is sensitive enough to respond to a single photon of light [11] and is about 100 times more sensitive to a single photon than cones. Since rods require less light to function than cones, they are the primary source of visual information at night (scotopic vision). Cone cells, on the other hand, require tens to hundreds of photons to ...
The normal human observer's relative wavelength sensitivity will not change due to background illumination under scotopic vision. The wavelength sensitivity is determined by the rhodopsin photopigment. This is a red pigment seen at the back of the eye in animals that have a white background to their eye called Tapetum lucidum.
At moderate to bright light levels where the cones function, the eye is more sensitive to yellowish-green light than other colors because this stimulates the two most common (M and L) of the three kinds of cones almost equally. At lower light levels, where only the rod cells function, the sensitivity is greatest at a blueish-green wavelength.
It is a light-sensitive receptor protein that triggers visual phototransduction in rods. Rhodopsin mediates dim light vision and thus is extremely sensitive to light. [6] When rhodopsin is exposed to light, it immediately photobleaches. In humans, it is regenerated fully in about 30 minutes, after which the rods are more sensitive. [7]