Why did my MEDIUM REDDISH BROWN turn WAY dark red?

I like it, but I`m just curious as to WHY that happened. I had light brown/DARK blonde hair to start with and since previous experiences have taught me that my hair sucks up dark colours, I only left it on for 25 of the recommended 30 minute set time.
So now I`m a redhead :) NOt BAD, like I said, I dont mind the color... I was just expecting something a little more, oh i dont know, Brown?
It was Loreal Preference, and I`ve used that shade twice before with good results.. this is the first time it`s come out this red :)

Any thoughts would be much appreciated!

The reason that your hair is went darker when you applied the color, is it is more porous and readily accepts color much easier, which results in a deeper "depositing" of the color pigments. To try to combat this use a good intensive conditioner just before coloring and lightly rinse, towel dry thoroughly before coloring and apply color to the midshaft and roots first and to ends last.