iPhone auto brightness I reset the settings (all settings) on my new iPhone 5 today, to try to troubleshoot some problem. Since doing so, my screen seems dimmer. 

I never changed the brightness settings to begin with, from opening the factory-sealed box up until the reset, so I am not sure why this seems to be the case. The auto-brightness seems to be using a lower intensity for any given lighting condition since the reset.

Am I just imagining things, or is this possible?
You probably are just imagining things, unless dirt has been obstructing your ambient light sensor and beside resetting your settings, you cleaned it too.