This ring contains and LED connected to a wire coil. When the wire coil is properly aligned with an electromagnetic field, the LED will light up. This phenomenon is called induction. The electric current in a primary coil contained in a NFC reader or wireless charger creates a magnetic field which, in turn, creates an electric current in the coil cast inside the ring, lighting up the LED. This is the same technology that allows you to tap your card to board public transportation, or tap to pay. Make this ring and take it around town to discover how electromagnetic fields at work!
Note that the gauge of your wire, the circumference of the ring, and the color of LED, and whether your wire is coated will affect how many wraps you need to power the LED. With the recommended wire and a size 11 ring mold, 15 wraps will comfortably fit in the ring mold, and produce a bright LED. Also know that different charging devices (the primary coil) will give you different amounts of power, so the ring might not work with every charger the same way. Generally, the more wraps, the brighter your LED. If your LED does not seem to be working, try again with a increased number of wraps. I would do no less than 15. If you want to play it safe, go for the maximum number of wraps, with the lower power LED like yellow or red.