Screen Dims when Opened

You might check System Preferences>Energy Saver>Battery> If 'Slightly dim ...' is checked, uncheck it.

Exact same thing happens to me. I have noticed the computer stays on when the screen is closed, and also noticed this only happens while it's connected to external power, if on battery power the laptop does go to sleep as expected and wakes normally when opening the screen.

Otherwise I can hear the fan running and the bottom stays warm as if in use.

I've tried many things, changing the settings in System Properties, removing all plugged in devices... and I have not been able to figure out why this happens :-/

WORD FOR WORD, same thing keeps happening to mine and its a 2011 model 15" MBP 2.3(w/turbo), 8GB of self-installed RAM, Hi-Res Glossy Screen, and latest updates.

WHAT I TRIED TO FIX IT:

• I changed the display and power settings around but no success.
• I installed my own RAM but I put the orignal back in temporarily and it still did it, even after tampering with settings and running many restarts.
• I made sure there were no registry or start-up errors as I am strict about a clean, organized computer.

Is this a hardware or software error?!? I'd like to know why this is happening and how to fix it because its beginning to serioulsy agitate me.

This can happen if the ambient light sensor (just next to the iSight camera) thinks that it's dim, and you've got System Preferences -> Displays -> Automatically Adjust Brightness checked. Un-checking this value should help.

I've had this problem ever since I installed lion (2011 15" mbp). The only thing I have noticed is that when wifi is turned off the problem doesn't persist. It's a really weird connection. Still have not figured out why it does this. Was just hoping that mountain lion would fix the issue.

This same thing just stared happening to me, in exactly the same way. Did you ever figure out a way to fix it?

same thing here. i'm going to try heading to the apple store to see if they can fix the problem

This happens to my macbook pro. I've tried everything in this thread, but still dims, when I open my laptop.