: What is a good illustration (or example) of the Helmholtz–Kohlrausch effect? While reading on the Lab color space, I stumbled onto the Wikipedia page for the Helmholtz–Kohlrausch effect. I

@Murray664

A simpler example is comparing a blue led to a blue light bulb with the exact same color and luminance. The h-k effect says that the led will look brighter. This surprises us since we are accustomed to light source with the same color and measured luminance appear to have the same brightness. We just have to realize that brightness is not luminance. It has been said that luminance is a photometric parameter whereas brightness is a colorimetric parameter.

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@Marchetta832

I found this explanation:


CIE lightness is a psychophysical scale based on colourimetric
measurements, and may not quite coincide with lightness as experienced
by an observer, even under ideal conditions. In particular, certain
colours have a tendency to look lighter than a grey of the same CIE
lightness, an effect known as the Helmholtz–Kohlrausch Effect (Figure
8.1). In Photoshop, this can result in some small surprises when converting images to greyscale mode, which translates all colours to a
grey of the same value of CIE lightness.


There is also an image explaining this, take a look at figure 8.1 in www.huevaluechroma.com/081.php


Figure 8.1. Helmholtz–Kohlrausch Effect. A: Various colours on a grey background, all measuring L = 50 in Photoshop. B: same image converted to greyscale mode.

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