My understanding is that oleds are a weird beast. Since there’s no backlight, each pixel can be considered a small colored light, if you have a fully black screen, then it’s essentially off and not using any power. However, there are instances where the peak brightness is limited to a small portion of the screen, because blasting the entire thing of full brightness white would pass the power supply capacity…

That said, let me stress this: it’s my understanding. Not a hard fact, I might be wrong or just basing things on old information.