i recently posted about the knog boomer usb bike lights, and was eager to give them a try. the original boomer design required two AA batteries per light, but essentially this design is exactly the same from the outside. the front and back lights, although almost identical in size, actually use different mouldings and attachments, as you can see from the above and below photos.
one of the things that would worry me about the design of the back light is the attachment. compared to the front light, it feels like the rubber moulding is a bit thin where it joins the clip. i presume they've been designed to sit flush down the seatpost, but i think it'd feel a lot stronger if it was identical to the front light. not too big a problem really though.
once you remove the rubber sleeve the sealed internals are revealed, and to get to the usb interface you simple remove the cap at the back. it is simple enough to use, you simple plug it in to an available port on your computer or laptop, or into a usb charger at the mains. each light took about 4 hours to charge from a usb port on my computer.
one thing for potential users to bear in mind is the size of it, as certain laptops and computers place usb ports very close together. the size of the light can prohibit you from putting anything next to it when it's plugged in, and similarly if you put it in a standard apple usb charger at a plug socket against the wall it struggles to fit. i use a usb hub so this wasn't really a problem, so if it's a problem i suggest you use something similar!
having said that, the rechargeable ability is the main strength of these lights, and the main reason you'd buy them. they do cost a bit more than the equivalent battery powered light, but regular commuters and cyclists will know that bike lights eat up batteries. although batteries can be comparatively cheap, it feels so much better to not be putting in new ones and throwing out old, but simply recharging them.
the lights are very bright compared to my previous lights, the knog frog's. they are marketed as 'secondary lights', which means they may not be suitable if you're cycling through the woods at night, but for a city cyclist these are plenty bright enough.
the front light is a super-bright white led with an output of up to 55 lumens, and the rear light has a super-bright central red led with two peripheral flashing leds, with an output of up to 15 lumens. with four modes each, the lights will last for 3.5 hours in steady mode, and up to 12 in flashing mode.
the lights are available in a range of colours, and cost around £35 each. it is a very nice design, and being able to recharge them is a real bonus. all awkwardness with charging them aside, the extra cost is well worth it when compared to the wastefulness of battery powered lights. i really think these lights are great, perfect for the city cyclist!