This LoRA slider affects the backlight. As with all sliders, the weights naturally depend on the prompt and the model used, and are therefore not set in stone.

Good results are achieved with weights between -3 (no backlight) and 6 (strong backlight).

This time, I created two grids with almost identical prompts to demonstrate the effects when the prompt contains backlight settings.

The first prompt lacks any backlight settings; in the second, I added "small bright light from behind." As you can see, the differences are dramatic.