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The concept of light and dark adaptation, discussing the range of light levels in the natural world, the importance of adaptation, the role of pupil changes, and the differences between rod-based and cone-based vision. It also covers the concept of Weber's Law and the response of visual neurons.
What you will learn
Typology: Exercises
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The range of luminances (left) and retinal illumination (right) found in the natural world Sun Fluorescent light/bulbs White paper, full sunlight Candle flame Comfortable reading Print read with difficulty White surface, moonlight Threshold for cone vision White surface, moonless night Visual threshold
The ratio of light intensities reflected from the white surround and the black letter is 9:1 under both low and high illuminations.
Luminance difference between ‘L’ and background = 80 units 8000 units Background = 90 units 9000 units Response ∝ Difference/Background 80/90 (89%) 8000/ (89%)
A piece of white paper that is dimly lit (A) looks white because its luminance lies at the top of its local scale, even though this luminance may be less than that of a piece of black paper that is brightly lit (B). log illuminance log luminance
Convergence receptors 130 million bipolars 20 million ganglion cells 1 million optic nerve fibres
Relative sensitivity Wavelength (nm)
High Time in dark (min) 7 minutes
Duplex function
Large operating range but poor contrast sensitivity Relative light intensity Intensity Brightness Brightness Good contrast sensitivity but small operating range