googled "light reduce" and nissan and came up with this:
Maxima and Cefiro owners down under... - View topic - Cefiro Dash Switch
According to the antepenultimate post, it controls a headlight feature that turns off the headlights when the car is stopped (but keeps the parking lights on), and turns them back on when you start to move. I assume it is for city driving, so that if you are stopped in traffic or at a light, your headlights don't blind other drivers.