What does LRV on a paint tin mean? Slide the wall and see

The number on a paint tin called LRV tells you how much light a colour bounces back, from 0 (absorbs everything) to 100 (reflects everything).

Slide a wall from deep to light in a simple room and see how the light changes, and when a darker colour is a choice rather than a mistake. A few quick ways to use the number, without buying anything.