Beautifully minimal LED Advent wreath circuit and device

An “Advent wreath” is a horizontal wreath, traditionally with four candles which are lit successively to mark each of the four weeks of Advent in the liturgical calendar of some western-tradition Christian churches. Alexander Weber has produced an elegant little electronic version that uses 4 LEDs, a coin cell, a coin cell holder, a paperclip, and an 8-bit microcontroller chip. It is light-responsive, and uses one of the LEDs in “reverse” mode as a photodiode to detect darkness. The LEDs flicker, and the number of LEDs lit at any point is cycled by briefly cutting the power. Awesome design.