What does 120dB Wide Dynamic (High Dynamic) mean?

We often see that the parameters of a camera say that it supports 120dB wide dynamic, where 120dB is actually a ratio, which means that the ratio of the illuminance between the brightest part and the darkest part of the camera can be identified as 1 000 000:1, that is, 106: 1.

Why is 106:1 corresponding to 120dB?

It is due to this artificially defined wide dynamic ratio formula:

dB = 20 log (illuminance of brightest part [lx] / darkest part [lx] )

20log(1 000 000/1)=20 X 6=120dB

In essence dB is a ratio, a pure counting method, without any unit notation.  It has different names in different fields, so it also represents different practical meanings. Such as sound volume, signal strength, etc.

The meaning of dB is to represent a very large number (followed by a long string of 0s) or very small (with a long string of 0s in front of it) relatively short.

For example, expressing a wide dynamic range as 120dB is obviously more intuitive and concise than using 1 000 000:1.

Other fields, for power, dB = 10Xlog(). For voltage or current, dB = 20Xlog().

In the field of displays and further more the security industry, 120dB is also a special ratio and the dynamic range that the human eye can recognize is about 120dB.

This means that a camera with a wide dynamic capability of 120dB can recognize a dynamic range comparable to that of the human eye.