A Supernova E3 Taillight can be used with the Beacon as long as a 60Ω resistor is placed in series between headlight and taillight.

In a pinch, a 100Ω resistor can be used, although the taillight will be dimmer.  100Ω is more likely to be available from an electronics store.  At least 0.5W is recommended.

For more information, see our page on taillight compatibility.