The big divination well

8hours work/piece

An arrow appears at the bottom of the well when you move a rock specially adapted to the switch/process is 3 LED blacklighted.

The text/arrow appears only in the dark:

Presented with an enigma: When stones walk at night, ways become brighter : The arrow(or whichever symbol/small text you want me to write  appears when you move the rock and shut the light!