Bloch's law observes that, for brief presentations, the product of luminance (or contrast) and duration at the detection threshold is constant. The law is due to Adolphe-Moise Bloch, who first formulated it in 1885.
Derivation
Consider that a brief flash of intensity
is presented for a duration
. Bloch's law states that detection occurs if the total luminance energy
exceeds some threshold value
. Formally,
Here,
is a constant that can vary with different viewing conditions, observer attributes, and adaptation levels. Early measurements used single, isolated light flashes of varying duration and intensity to determine the boundary at which a viewer first reports seeing the flash. When plotted against detection thresholds, these data typically exhibit a near-constant product of intensity and duration for short intervals.
See also
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Ricco's law
Riccò's law, discovered by astronomer Annibale Riccò, is one of several laws that describe a human's ability to visually detect targets on a uniform background. It says that for visual targets below a certain size, threshold visibility depends ...
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Temporal summation
Summation, which includes both spatial summation and temporal summation, is the process that determines whether or not an action potential will be generated by the combined effects of excitatory and inhibitory signals, both from multiple simultan ...
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Contrast (vision)
Contrast is the difference in luminance or color that makes an object (or its representation in an image or display) visible against a background of different luminance or color. The human visual system is more sensitive to contrast than to absol ...
References
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Photometry