<p>In general, subjective sensation increases linearly with the the log of physical intensity, which is described by <a href="https://en.wikipedia.org/wiki/Weber%E2%80%93Fechner_law" rel="nofollow">Fechner's law</a>. </p>

<p>We are sensitive to small variations when light is dim, but we need large differences in intensity under conditions of high luminance (<a href="https://en.wikipedia.org/wiki/Weber%E2%80%93Fechner_law" rel="nofollow">Weber's law</a>). This is a linear relation, but taken together with Fechner these findings are described as the widely-known <a href="https://en.wikipedia.org/wiki/Weber%E2%80%93Fechner_law" rel="nofollow">Weber-Fechner's law</a>, justifying the log scales used. </p>

<p>Another well-known example is the <a href="http://www.animations.physics.unsw.edu.au/jw/dB.htm" rel="nofollow">decibel scale</a> in hearing, which is also a log scale.</p>

<p>Any basic textbook on perception or psychophysics will explain this and a reference is added below.</p>

<p><sub><strong>Reference</strong><br>
<strong>-</strong> <a href="http://www.psy.unipd.it/~masin/Masin-2009d.pdf" rel="nofollow">Masin <em>et al.</em>, <em>J History Behav Sci</em> (2009); <strong>45</strong>(1): 56–65</a></sub></p>

CC BY-SA 3.0
2015-10-06T14:01:42.860Z
2015-10-06T20:52:38.763Z
2015-10-06T20:52:38.763Z
AliceD
<p>Are there any papers which justify converting into log luminance? For example papers showing humans being sensitive to changes in log luminance rather than luminance <em>per se</em>?</p>

<perception><vision><psychophysics><sensory-perception>
In psychophysics, why are log luminance rather than absolute luminance values reported?
Lenna
# In psychophysics, why are log luminance rather than absolute luminance values reported?

(Asked by: username_0 on 2015-09-01)

Are there any papers which justify converting into log luminance? For example papers showing humans being sensitive to changes in log luminance rather than luminance *per se*?

**Tags:** perception, vision, psychophysics, sensory-perception


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## 1 answers

### Answer by username_1 on 2015-10-06. Score: 5

In general, subjective sensation increases linearly with the the log of physical intensity, which is described by [Fechner's law](https://en.wikipedia.org/wiki/Weber%E2%80%93Fechner_law).

We are sensitive to small variations when light is dim, but we need large differences in intensity under conditions of high luminance ([Weber's law](https://en.wikipedia.org/wiki/Weber%E2%80%93Fechner_law)). This is a linear relation, but taken together with Fechner these findings are described as the widely-known [Weber-Fechner's law](https://en.wikipedia.org/wiki/Weber%E2%80%93Fechner_law), justifying the log scales used.

Another well-known example is the [decibel scale](http://www.animations.physics.unsw.edu.au/jw/dB.htm) in hearing, which is also a log scale.

Any basic textbook on perception or psychophysics will explain this and a reference is added below.

**Reference**  
**-** [Masin *et al.*, *J History Behav Sci* (2009); **45**(1): 56–65](http://www.psy.unipd.it/~masin/Masin-2009d.pdf)


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