Enviroment gets increasingly brighter when running

Hi,

Am a newbie to Unity, was following a Youtube tutorial on creating a endless runner 3D game. was trying to get it to repeat section. But problem is, the enviroment get's brighter and brighter once the game runs. What is wrong with the code below? Thanks! :)`enter code here`

 public class GenerateLevel : MonoBehaviour
 {
     public GameObject[] section;
     public int zPos = 39;
     public bool creatingSection = false;
  
     public int secNum;
 
    
     void Update()
     {
         if (creatingSection == false)
         {
             creatingSection = true;
             StartCoroutine(GenerateSection());
         }
     }
     IEnumerator GenerateSection()
     {
      
         secNum = Random.Range(0, 3);
         Instantiate(section[secNum], new Vector3(0, 0, zPos), Quaternion.identity);
         zPos += 39;
         yield return new WaitForSeconds(2);
         creatingSection= false;
     }
 }