I’m all for the idea of making us cyclist more safe on the roads. But this one is only a gimmick.
The Firefly bicycle light uses a passive Infrared sensor to detect vehicles approaching from behind – the closer they get the brighter it shines. Its other clever trick is that it uses a set of white LEDs to illuminate the rider’s back and the road beneath the bike.
I take it that this is to be used at night, but if other road users fails to see you with your normal rear light in normal your riding position. Then they will still fail to see you with this on. Its up there with the laser light I talked about a few weeks ago.