Moving axis lights display
stepper motors are able to generate electricity,
if the printer is turned off, moving the X or Y axis causes the associated stepper motor to turn. this generates a voltage in the stepper motor which is then rectified in the stepper driver, by the protection diodes, and dissipated in the einsy controller.
there are two schools of thought on this subject,
1, moving the motors whilst the printer is switched on, is BAD MOJO, and you should never do it.
2, Motors are inductive devices and the stepper drivers have built in protection for the associated electronics, just in case the motors are moved...
I take the second view!