The lamp

The control on this lamp though obvious is not necessarily intuitive.
Is the control a button or a knob, do you turn or push? There are
affordances for both. The control has a rough surface, ridges, that
suggest turning because they provide friction. However, the control
also allows enough movement which also suggests push. The correct
choice is that it is a knob and that turning it clock-wise turns on the
lamp.

-Gabe Schwartz