Plants (and algae) pearl when the water around them is so saturated with oxygen that the oxygen they produce as a result of photosynthesis can't dissolve in the water.
I think you get loads more pearling at water changes because tap water is at a higher pressure and therefore has more dissolved oxygen (and CO2).
For my current tank, on non-water change days, there is usually pearling about an hour after lights on, especially near the surface. Lower plants take longer to show pearling.
When I take photos of my tank in the evening, I turn the LEDs up to 11 and the plants begin to pearl like crazy. The response is immediate. So overall I think you need loads of CO2 and light for plants to pearl.