Design submitted by Logan from the USA.
Logan uses UV LEDs that emit no visual light for this watch design. The LEDs are never seen directly, but their UV light activates fluorescent paint that shows the time.
One digit is displayed at a time. The LEDs turn on and off one-by-one in a sequence that “draws” the digit on the fluorescent paint. After the digit has been drawn and all LEDs are off, the digit fades and the next digit is drawn. The LEDs’ optics create wide-angle beams so the light from the adjacent LEDs overlaps and activates a continuous line of paint. An anti-UV coating on the top of the glass prevents sunlight from activating the paint, so the watch stays black until the UV LEDs turn on.