Can Win 7 cause display to become less bright?

Hi,

I've had an Inspiron 6400 since spring of 2007. It came with Win XP pre-installed.

I steered clear of Vista, but last year I decided to give Win 7 a try on the Inspiron, despite it failing the Dell compatibility test.

Despite what Dell said, Win 7 installed fine on the machine, and it runs sweetly. (Surprisingly, even quicker than with XP...)

I do remember, during the Windows compatibility check (as opposed to the Dell one) there was mention made of a potential problem with the display, as the Inspiron didn't have the right sort of adapter or something. (I can't remember exactly what it said.)

As I say, Win 7 has run sweetly since install, but now the summer is here and I'm taking it outside, I am sure that the display is less bright than it was last summer under XP. All the power save modes are set for full brightness, and repeated pressing of function + up arrow makes no difference either. But I can hardly see what is on the screen when I am outside with the machine.

I appreciate this is a bit subjective; it may just be my eyes that have become less sensitive or something, but I doubt it.

Could it possibly be something to do with the Win 7 installation at all? Would it be worth my while reverting to XP?