! WARNING !
Dealing with mains voltage is no joke, please be careful
Running your LEDs from AC voltage is pretty efficient, you can light up a whole lot of LEDs with little effort. Most Christmas lights you buy nowadays already do this, but as Matt points out in the video they flicker a lot. Matt decided to set up a bridge rectifier, and a capacitor to smooth out the flickering. As shown on the oscilloscope those simple modifications make a huge improvement!
Of course you can’t just plug the LEDs into the wall and expect it to work (and not catch fire). A little planning is needed. By calculating the collective voltage drop of the LEDs in series you can run a lot of LEDs with very little current limiting. Cool hack Matt.