Ipad 2 screen dims then brightens for no reason without touching

Ok this is going to sound a little confusing.
My ipad i use mnainly for reading epub books in the evening before bed.
I have the auto lock turned on so that the screen will simply sleep after 2 min

NOw when ive finished a chapter and want to sellp i leave the ipad alone, no interaction and let it sleep. Recently i havenoticed that the screen will dim and then brighten as if i had touched it. It will then dim again and then fall asleep.

In this order: Dim - Brighten without interaction - Dim - Sleep

Im confused that this happens when i let it sleep while leaving the ibooks app open so i can simply resume where i left off.

Is there something wrong with my ipad or am i worrying too much. I this a bug from the ibook app?
Any thoughts and insight would really help me.

Its still new maybe only a month at the most old. It was brought to me from the UK as a birthday present. I think it was on standby for the time it spent in transit from Manchester to Bangkok.

I little profesional opinion would be greatly appreciated.