Flashing, or ‘the halo effect’, is when patches become visible on a painted surface in certain lights/angles.
Flashing appears when two areas of a painted surface have been applied differently. In the example shown below, the wall was originally painted using a roller and has since been touched up using a paint brush. Flashing may not be visible at all times, but can be seen at certain angles or in a certain light.
Unfortunately the best way to resolve the issue of Flashing is to re-paint to the nearest whole elevation, ensuring the wet edge is maintained.