Color varies in energy flow per unit area {intensity, vision}. Vision can detect very low intensity. People can see over ten-thousand-fold light intensity range. Vision is painful at high intensity.
sensitivity
People can perceive one-percent intensity differences. Sensitivity improves in dim light when using both eyes.
receptors
Not stimulating long-wavelength or middle-wavelength receptor reduces brightness. For example, extreme violets are less bright than other colors.
temporal integration
If light has constant intensity for less than 100 ms, brain perceives it as becoming less bright. If light has constant intensity for 100 ms to 300 ms, brain perceives it as becoming brighter. If light has constant intensity for longer than 300 ms, brain perceives it as maintaining same brightness.
unchanging image
After people view unchanging images for two or three seconds, image fades and becomes dark gray or black. If object contains sharp boundaries between highly contrasting areas, object reappears intermittently.
bleaching
Eyes blinded by bright light recover in 30 minutes, as eye chemicals become unbleached.
If stimulus lasts less than 0.1 second, brightness is product of intensity and duration {Bloch's law} {Bloch law}.
Phenomenal brightness {brightness} {luminosity} relates to logarithm of total stimulus-intensity energy flux from all wavelengths. Surfaces that emit more lumens are brighter. On Munsell scale, brightness increases by 1.5 units if lumens double.
properties: reflectance
Surfaces that reflect different spectra but emit same number of lumens are equally bright.
properties: reflectivity
For spectral colors, brightness is logarithmic, not linear, with reflectivity.
factors: adaptation
Brightness depends on eye adaptation state. Parallel pathways calculate brightness. One pathway adapts to constant-intensity stimuli, and the other does not adapt. If two same-intensity flashes start at same time, briefer flash looks dimmer than longer flash. If two same-intensity flashes end at same time, briefer flash looks brighter than longer flash {temporal context effect} (Sejnowsky). Visual system uses visual-stimulus timing and spatial context to calculate brightness.
factors: ambient light
Brightness is relative and depends on ambient light.
factors: color
Light colors change less, and dark colors change more, as source brightness increases. Light colors change less, and dark colors change more, as color saturation decreases.
factors: mental state
Brightness depends on mental state.
brightness control
Good brightness control increases all intensities by same amount. Consciousness cannot control brightness directly. Television Brightness control sets "picture" level by increasing input-signal multiple {gain, brightness}. If gain is too low, high-input signals have low intensity and many low-input signals are same black. If gain is too high, low-input signals have high intensity and many high-input signals are same white. Television Brightness control increases ratio between black and white and so really changes contrast.
Detected light has difference between lowest and highest intensity {contrast, vision}.
contrast control
Good contrast control sets black to zero intensity while decreasing or increasing maximum intensity. Consciousness cannot control contrast directly. Television Contrast control sets "black level" by shifting lowest intensity to shift intensity scale. It adjusts input signal to make zero intensity. If input is too low, lower input signals all result in zero intensity. If input is too high, lowest input signal results in greater than zero intensity. Television Contrast control changes all intensities by same amount and so really changes brightness.
Mind can detect small intensity difference {contrast threshold} between light and dark surface area.
Larger objects have smaller contrast thresholds. Stimulus-size spatial frequency determines contrast-threshold reciprocal {contrast sensitivity function} (CSF). Contrast-threshold reciprocal is large when contrast threshold is small.
Visual system increases brightness contrast across edge {edge enhancement}, making lighter side lighter and darker side darker.
If eyes are still with no blinking, scene fades {fading} [Coppola and Purves, 1996] [Pritchard et al., 1960] [Tulunay-Keesey, 1982].
Human visual systems increase brightness contrast across edges, making lighter side lighter and darker side darker {Mach band}.
Leaving, arriving, or transmitted luminous flux in a direction divided by surface area {luminance}. Constant times sum over frequencies of spectral radiant energy times long-wavelength-cone and short-wavelength-cone spectral-sensitivity function [Autrum, 1979] [Segall et al., 1966]. Luminance relates to brightness. Lateral-geniculate-nucleus magnocellular-cell layers {luminance channel, LGN} measure luminance. Light power (radiance) and energy differ at different frequencies {spectral power distribution}, typically in 31 ranges 10 nm wide between 400 nm and 700 nm.
Light {luminous flux} can shine with a spectrum of wavelengths.
Light sources {illuminant} shine light on observed surfaces.
Light {radiant flux} can emit or reflect with a spectrum of wavelengths.
Radiant flux in a direction divided by surface area {radiance}.
Radiant flux divided by surface area {irradiance}.
1-Consciousness-Sense-Vision-Physiology
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Date Modified: 2022.0225