Lighting continuity is about the creative choice to maintain or willingly not maintain lighting consistency throughout a sequence of shots. The reason behind deliberately ignoring lighting continuity is to achieve better lighting. Its that simple.
Needless to say that there should be a good reason not to maintain continuity. A couple of examples were continuity was ignored in favor for better lighting.
The examples above cover cases in which the continuity across multiple shots is ignored in favor for better lighting. There are situations though in which a different key light direction within the same shot can improve the lighting a lot. A great example can be found in ‘Tucker: The Man and his Dream’ from Cinematographer: Vittorio Storaro
At the beginning of the shot Martin Landau is lit with a strong light from left side, while at the end he is lit from the right with a softer and much darker light. The transition between the two key light direction is done during the camera moving from right to left clever hidden by Jeff Bridges in front of the camera. There is just a fraction of a second were the left and right key are visible at the same time.
Its a great showcase that you can get away with changing the light direction, softness, exposure even within a single shot.
Lighting continuity in CG:
Maintain the same lighting setup in CG is a simple task. No matter if its across the same sequences or if the shot to match has been done months ago. Export/import the rig and all the lights are at the exact same spot, with same colors and intensities. Even though the lights match perfectly this way camera, character poses, orientation and location might differ with the potential result of them being badly lit. In this case lighting continuity should be ignored in favor for better lighting instead of matching continuity with bad lighting. Achieving better lighting based on a existing setup shouldn’t take too much time. Like in the examples shown on this page mainly the key and rim lights hitting the actors needed some adjustments. Adjustments that are clearly worth the extra effort.