Confirmed with my iPad mini 2 too. But I didn't notice it until I saw this post.Noticed it happens on my iPad Mini 2 too.
Must be an iOS 8.1 bug.
Only happens for a split second as you open Safari.
If you take a screenshot, and open it up as a picture the brightness doesn't flicker, so it's definately software. I'm sure it'll be fixed with the next update.