Would you be interested in having the addition of an in-game lighting setting?
Not just for effects in Forge but in general for the game entirely.
It wouldn’t function the same way as brightness as that merely increases/decreases the display lighting.
Instead, lighting from various sources within the game itself could be customised; reduced/increased by the individual user for certain effects whilst things such as the HUD, menus, text remain the same. Which reminds me; would you also be interested in having a customisable HUD?
Halo 5 uses baked and pre-calculated lighting. Without boring you with technical details, it would be impossible to implement beyond basic “lights” that don’t actually cast light.