This is common amongst many growers.
If you have a lumen meter you can see that the sunlight when "sunny" will put out lots of lumens.
Also the sunlight is natural like the plant ya know.
They seem to want to stretch a litte more.
I put mine in the sun for like 4-5 hrs when it is nice out.
Just to give it a rest from the cfl's. I would not put mine out longer becuase I have limited space. I like the nodes to stay as close together as possible.