Talk:Ricco's law

Formula

Is this formula accurate? In a class I'm taking we just learned Ricco's Law as "luminance x area = k".Garvin 05:51, 27 April 2007 (UTC)

I share this doubt, at least there is a misinterpretation of the fact, that in order for the stimulus to be/remain visible either the intensity has to be increased or the area. This leads to "intensity x area = constant" at the detection limit.

Please refer to: http://webvision.med.utah.edu/book/part-viii-gabac-receptors/visual-acuity/

8. Spatial Summation

Spatial summation describes the eye’s ability to summate or add up quanta over a certain area. This area over which spatial summation operates is called the critical diameter. According to Ricco’s Law, within this critical diameter, threshold is reached when the total luminous energy reaching a constant value (k). Threshold is reached when the product of luminance (L) and stimulus area (A) equals or exceeds this constant value. In another words, when luminance is halved, a doubling in stimulus area is required to reach threshold. When luminance is doubled, the stimulus area can be halved and still reach threshold.

Ricco’s Law is expressed as:

L x A exp(n) = k

where L is the luminance of the stimulus, A is the area of the stimulus, k is a constant value and n describes whether spatial summation is complete (n=1) or partial (0<n<1). No spatial summation occurs when n = 0. Critical area varies with eccentricity. Ricco’s Law holds for an area of 30 minutes of arc in the parafoveal area (4 to 7o eccentricity) and increasing to an area of about 2o at an eccentricity of 35o (Davson, 1990). panjasan (talk) 15:21, 15 January 2014 (UTC)

You are right – the equation was misleading in that the connection to contrast was not drawn and, furthermore, the Wikipedia link to contrast was wrong: Contrast, in vision science, is defined differently than Display contrast. Strasburger (talk) 17:03, 4 July 2020 (UTC)

Also, although the above formula might be a good descriptor of the data, only for n=1 is it called Riccò's law. For n=1/2 it is sometimes called Piper's law. Strasburger (talk) 16:08, 8 April 2023 (UTC)

Ricco, Piper and De Vries-Rose laws are all approximate laws that hold under certain conditions, with Ricco being the most accurate. I've submitted a draft article on DeVries-Rose law for review, and might get round to doing one on Piper if no one else does.

https://en.wikipedia.org/wiki/Draft:De_Vries_-_Rose_Law StormBarn23 (talk) 17:58, 15 April 2023 (UTC)

Hi StormBarn23, in case it helps we have section on Riccò's and Piper's law in our review paper on peripheral vision 2011 Strasburger (talk) 15:24, 16 April 2023 (UTC)

References