One of the things that I was hesitant about this laptop was the brightness that a lot of reviews were mentioning. I went ahead and ordered the laptop and after a week, I was getting annoyed at the auto dimming. I disabled the auto dim in settings but it was dimming on dark websites and brighten up on websites where there was more white on the page. It wasn't because of the outside light source, but seemed to dim based on the brightness of the webpage itself.

After much research, I ran across this fix in the Dell forums:

http://en.community.dell.com/support-forums/laptop/f/3518/t/19455427?autolike=15120322-3f78e03a-9f7a-45a3-a545-81d85af3635a

With some slight modification to his steps in the verified answer, for the Dell 15 7558:

Right-click on the desktop, select "Graphics Properties..."

Click "Power"

Select  "On battery"

Disable "Display Power Saving Technology"

Click "Apply"

No more irritating display flickering, adaptive brightness or whatever you want to call it.  IMHO, it's an annoying feature that should be disabled by default."

Now the screen gets bright and stays bright. It's not the brightest screen I've ever used but it does seem to be worlds better. Now I'm extremely happen with my choice.