static public void SetLightGroup(LightGroup defaultLightGroup)
    {
        var lightGroups = Object.FindObjectsOfType(typeof(LightGroup)) as LightGroup[];
        var lightGroup  = defaultLightGroup;

        if (lightGroup)
        {
            BulletTime.DisableLightGroups(lightGroups);
            BulletTime.SetActiveLightGroup(lightGroup);
        }
    }