Graphical settings

Hello, I added settings option to my game, where you can chose between low, medium, and high graphics. And i faced a problem. My game runs a script at the begining of the game where it gets the current setting from PlayerPrefs and then sets the correct graphics level, however, sometimes the ligthing will stay dark Example:

The darker picture is the bug, it should be always light. It's some lighting related problem.

Here is piece of code where the script will change graphics.

 currentSetting = PlayerPrefs.GetString("Graphics");
 
         Application.targetFrameRate = 60;
 
         if (currentSetting == "low") 
         {
             terrain.heightmapPixelError = 200;
             terrain.basemapDistance = 1;
             QualitySettings.currentLevel = QualityLevel.Fastest;
         }
         if (currentSetting == "med") 
         {
             terrain.heightmapPixelError = 25;
             terrain.basemapDistance = 60;
             QualitySettings.currentLevel = QualityLevel.Simple;
         }
         if (currentSetting == "high") 
         {
             terrain.heightmapPixelError = 10;
             terrain.basemapDistance = 100;
             lights.shadows = LightShadows.Soft;
             QualitySettings.currentLevel = QualityLevel.Fantastic;
         }

P.S any ideas of another important settings that can increase performance? The idea is so low settings will be as optimized as possible even if graphics will look crap, but so high settings will look amazing.