Motion sensors are calibrated to detect anything moving about in the server rooms. When left vacant, they'll shut off the overhead lights to save on electricity. In the dark, the lights of the servers are left to glow smoothly through the night. Photo 9 of 15 in A Rare Glimpse of Google's Data Centers by Skylar Bergl

A Rare Glimpse of Google's Data Centers

9 of 15

Motion sensors are calibrated to detect anything moving about in the server rooms. When left vacant, they'll shut off the overhead lights to save on electricity. In the dark, the lights of the servers are left to glow smoothly through the night.