According to recent AMA klamacz (reforger project lead) on reddit: Reforger has the same system as Dayz, which adds grain effect during night time, if player increase Gamma settings on monitor.
But I can confirm that there is no any grain effects in the current reforger stable build, and you can increase gamma
proof: https://www.reddit.com/r/ArmaReforger/comments/1i9ht1b/gamma_boosting_is_extremely_broken_280_gamma_in/