Above image is from Wikipedia.

Tip: if it does not work at all, try switching the wires of the inductor. It's easy to get it wrong with them being paired.

I purchased some candle LEDs to put in the circuit and they seem to work quite well.

One disadvantage of this circuit that I did not foresee was the noise. There is a very high pitched noise coming from the coil ("coil whine"). I could have tried making the frequency even higher (maybe with a different coil) but I'm afraid my cats will not like that, since apparently cats can hear up to 65 kHz or so.

Idea: Purchase a 'bat-detector' to find sources of high frequency noises. Or maybe even a better idea: Make one!

To hopefully lessen the coil whine, I put glue (BISON kit transparent glue) all around the coil. And after a day waiting for it to harden, I notice it works! I hear no more irritating noise. Actually...after a while I do notice it again but barely audible. Is there anything else to be done?