Either tweet using the #LampSquare OR using the LampSquare location if you are nearby.
The @LampSquare twitter account will respond with a live picture of the lamp.
Using Foursquare / Swarm:
Step 1 - Go to Park Slope, Brooklyn and make sure you are facing the window described above.
Step 2 - Open Swarm on your mobile phone and check-in to the location called "LampSquare" to turn the lamp on.
Curious about the upgrade to "3.0"? Click here.