I like the setting of your game. There is a flicker of hope with all its bleakness. 

I am a bit confused about the mechanic. What target score should the GM set? What do you mean by roll dice equal to %light*ability? Do you roll a number of dice? If I ignore that line, I would assume the ability score is just a modifier to add to the results of a roll.

I like the theme/setting/story. The light mechanic is a lot vague. If these are "regular" flashlights, then batteries for continuous use would last maybe two days, or if on LED, seven at most. That's 24-hour use. Even if taken in shifts, calculating the percentage is tricky. If it were a self-recharging flashlight (i.e. had a built in dynamo) then one could make a 24-hour arrangement before useful light is gone. Yeah, the balance between describing the game flavor (actually important to the players) versus filling in the mechanics gaps (also important) came a little short on this one. I'd like to see a revised version soon after voting is done.

Darkness disease is a very cool concept. 4 weeks to death by malnutrition is a clear and meaningful time limit. No guidance for GM on what an appropriate target score would be. Light's influence on final result is interesting, but use of percentage is difficult to grasp and resolve.