The website gives an example of Weber\'s law, ?I/I = K, applied to weight. Let\'

Question

The website gives an example of Weber's law, ?I/I = K, applied to weight. Let's assume that Weber's law also holds for luminance (brightness).

We have a research participant whose just noticeable difference for a stimulus with a luminance of 20 kcd/m2 is a change in luminance of 1 kcd/m2. What does Weber's law predict will be that participant's just noticeable difference for a stimulus with a luminance of 100 kcd/m2?

Note: You can ignore the units for the purpose of answering this question, but for reference, luminance is measured in candelas (cd) per square meter (m2).

Explanation / Answer

According to Weber's law ?I/I = K

So from this, we know that for the luminance of magnitude, I = 20 kcd/m2, the increment threshold for detecting a difference was a ?I = 1 kcd/m2. K is then = 1/20= 0.05.

Hence, for 100 kcd/m2, the just noticeable difference would be = 0.05*100= 5 kcd/m2.

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