Mesopic vision

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Published on November 28, 2024 12:00:00 AM ● Video Link: https://www.youtube.com/watch?v=nogKpkWKz_E

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Mesopic vision, sometimes also called twilight vision, is a combination of photopic and scotopic vision under low-light (but not necessarily dark) conditions. Mesopic levels range approximately from 0.01 to 3.0 cd/m² in luminance. Most nighttime outdoor and street lighting conditions are in the mesopic range.
Human eyes respond to certain light levels differently. This is because under high light levels typical during daytime (photopic vision), the eye uses cones to process light. Under very low light levels, corresponding to moonless nights without artificial lighting (scotopic vision), the eye uses rods to process light. At many nighttime levels, a combination of both cones and rods supports vision. Photopic vision facilitates excellent color perception, whereas colors are barely perceptible under scotopic vision. Mesopic vision falls between these two extremes. In most nighttime environments, enough ambient light prevents true scotopic vision.
In the words of Duco Schreuder:
As a result of guadually switching from cones to rods in processing light, a number of visual effects occur:The rods have a different wavelength sensitivity, causing blue objects to appear brighter and red objects to appear darker. This is called the "Purkinje shift". - Color appears desaturated and hues change, drifting towards a dull purple. - Spatial acuity decreases linearly with log-luminance. A varying "noise" slowly becomes more prominent.
Cinematographers intentionally emulate mesopic effects to make scenes look darker than a display can actually achieve.

Source: https://en.wikipedia.org/wiki/Mesopic_vision
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