I am going to have bamboo click lock floor installed in a couple of weeks. The new floor will be going in 2 adjoining living rooms and a "T" shaped hallway.

What I am not sure about is how to run the planks. Should I go parallel along the longest wall, (which would also be going in the same direction as the light sources), but would require a direction change at the hallway, or go perpendicular to the longest wall, and have the planks run parallel to the hallway?

The contractor installing the floor says to keep all planks going the same direction and just choose what I want for the main rooms. He says the hallway is not really important, and if the planks go the short way across it, it will still look good.

Do you guys have any opinions?

I have always preferred a consistent (same direction) look as you get a nice flow appearance throughout the entire layout. Direction changes are pretty rare in most cases. I'd also run the flooring perpendicular to the main entry. This typically makes the areas look larger from that vantage.