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The Creation of Light by Gustave Doré. Darkness is the condition resulting from a lack of illumination, or an absence of visible light.. Human vision is unable to distinguish colors in conditions of very low luminance because the hue-sensitive photoreceptor cells on the retina are inactive when light levels are insufficient, in the range of visual perception referred to as scotopic vision.
Scotopic vision occurs at luminance levels of 10 −3 [7] to 10 −6 [citation needed] cd/m 2.Other species are not universally color blind in low-light conditions. The elephant hawk-moth (Deilephila elpenor) displays advanced color discrimination even in dim starlight.
The opposite problem, known as hemeralopia, that is, inability to see clearly in bright light, is much rarer. The fovea is blind to dim light (due to its cone-only array) and the rods are more sensitive, so a dim star on a moonless night must be viewed from the side, so it stimulates the rods. This is not due to pupil width since an artificial ...
Low light and lack of color of this sort may be associated with depression and lethargy. This association was made as far back as the 2nd century by the ancient Greek physician, Aretaeus of Cappadocia , who said, "Lethargics are to be laid in the light and exposed to the rays of the sun, for the disease is gloom."
The pupillary light reflex (PLR) or photopupillary reflex is a reflex that controls the diameter of the pupil, in response to the intensity of light that falls on the retinal ganglion cells of the retina in the back of the eye, thereby assisting in adaptation of vision to various levels of lightness/darkness.
The opposite problem, the inability to see in bright light, is known as hemeralopia and is much rarer. Since the outer area of the retina is made up of more rods than cones, loss of peripheral vision often results in night blindness. Individuals with night blindness not only see poorly at night but also require extra time for their eyes to ...
Beam of sun light inside the cavity of Rocca ill'Abissu at Fondachelli-Fantina, Sicily. The speed of light in vacuum is defined to be exactly 299 792 458 m/s (approximately 186,282 miles per second). The fixed value of the speed of light in SI units results from the fact that the metre is now defined in terms of the speed of light.
The Young-Helmholtz trichromatic theory of color vision postulated that there were three types of photoreceptors in the eye, each sensitive to a particular range of visible light: short-wavelength cones, medium-wavelength cones, and long-wavelength cones. Trichromatic theory, however, cannot explain all afterimage phenomena.