Just because you think the light should make a difference doesn't mean it always will.
Sometimes, it seems like it will be dark enough to use a light, (in the real world), and it actually does not make a difference.
I think there are times when a light should work, while the clock says it's daytime. This could be a change to the game that requires a large investment of time.
One idea that could help:
Darkness is an effect, that is localized to players.
Using a light creates a cone that adds transparency to the dark effect.
This would also help thwart gamma-modders who are using gamma to gain unfair advantages. (The darkness is real particles, not just lower exposure.)
Then you just add a little game logic that toggles darkness on or off for players based on conditions. (We can copy some of the code for rain logic.)