What is the perceptual threshold for vision?

The perceptual threshold for vision is typically defined as the minimum amount of light that is required for an observer to consciously perceive a light stimulus. This threshold can be measured in terms of the amount of light energy that falls on the retina of the eye, or in terms of the luminance of the stimulus.

The absolute threshold for vision is the minimum amount of light that can be detected by the human eye. It is typically measured in terms of the luminance of the stimulus, which is the amount of light energy per unit area per unit solid angle. The absolute threshold for vision varies depending on the wavelength of light, with the eye being most sensitive to light in the yellow-green part of the spectrum. For the average human eye, the absolute threshold for vision is about 0.01 cd/m2.

The difference threshold, also known as the just noticeable difference (JND), is the minimum difference in stimulus intensity that can be detected by the human eye. It is typically measured in terms of the percentage change in stimulus intensity required for a person to notice a difference. The difference threshold for vision varies depending on the stimulus intensity, with the eye being less sensitive to small changes in intensity at high intensities than at low intensities. The difference threshold for vision is about 1%-2% for most people.