### photon noise

**(shot noise, Poisson noise)**
(variation in light measurement due to its quantum nature)

**Photon noise** (or **shot noise** or **Poisson noise**)
is variation in the measurement of electromagnetic radiation due to
its quantum nature, i.e., if the number of incoming photons is
small, the rate at which they trigger a detector
can vary through pure chance.
The concept was introduced in 1918 by Walter Schottky.

In astronomy, clear, unambiguous observation of
distant objects may be limited by photon noise.
The noise in a finite observation follows a Poisson distribution,
which with enough photons, is virtually **Gaussian**
(i.e., the **normal distribution** described by the Gaussian function).
However, astrophysics is getting what you can out of
however small amount of data you can acquire,
so disentangling the photon noise (and thermal noise)
from the signal is of interest, and efforts are made to model the
various components mathematically to untangle signal from noise.
The term **shot noise level** (or **Poisson level**) refers
to the degree of photon noise that is contributing
to the resulting signal/noise mix.

(*instruments,EMR*)
http://en.wikipedia.org/wiki/Shot_noise

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