Hello! "flickering" is when a source of light turns on and off, or is blocked and then unblocked, in quick succession. and "shimmering" is when a light is reflecting gently and appears to be moving - but is constant. I hope that helps!

Usually 'flicker' will be used to describe brightness that's more intense and rapid. For example, an unsteady fire/ lights when they're just turning on /the effect you see in horror movies when something bad is about to happen 😂. Shimmer would be used to describe the reflection of light that's softer and slower, like glitter or the surface of the water.

Flicker is a source of light that is shining unsteadily. Shimmer is soft, wavering light.