Q: I have a stain on the left side of the screen light brown suddenly appeared

Hello Amirbar,

For more information on this, take a look at this article:

How to clean Apple products

http://support.apple.com/kb/HT3226?viewlocale=da_DK

If the image is too dark, adjust the brightness. In General Settings choose Brightness and Wallpaper and slide the slider.

iPhone: Hardware troubleshooting

http://support.apple.com/kb/TS2802

Have a nice day,

Mario