Following is a crop from a RAW shot, developed in Lightroom 5.7, into a setting sun from a Sony A77II – ISO 100, f/5, 1/20s, with a TTL fill flash.

In the darker regions near the sun a series of horizontal lighter lines can be seen. What causes these?

[![Light banding near sun](https://i.stack.imgur.com/gVcdx.jpg)](https://i.stack.imgur.com/gVcdx.jpg)

[Here is the same image with contrast cranked up to make it easier to see the bands](https://i.imgur.com/sTd4gEr.jpg). Starting from an arbitrary band, I counted the number of pixels separating each successive band and got the following sequence: 18, 24, 12, 24, 12, 18, 24, 12, 18, 18, 24, ...

My guess is that it might be the sensor equivalent of lens flare, in which case the question would be: what is the physical characteristic of the sensor that is being illuminated?