LED Bulbdial Clocks
Check out this ingenious use of LEDs, for time telling.
Basically, “Bulbdial” clocks rely on changing electric light to emulate the principles of sundials. Very impressive in their design, and they look like works of art.
“Rather than using three physically moving light sources at different heights, we use three rings of LEDs at different heights. Within each ring, we only turn on one LED at a time, so that we only have a single effective light source– it can light up at different places from within the ring. The three rings are located above one another so that they each project light onto the rod in the middle, making shadows of different lengths.”
For the full story read LED Bulbdial Clock shadows the time