Rating: 4 / 5
The RadTech iSight (http://www.radtech.us/Products/ISight.aspx) is a product you'd expect to see as a prop in a near-future scifi movie: a single-LED task light that wraps over the ear like a mobile phone headset. And that's what it is.
And it weighs 18 grams.
It's six times heavier than the Photon lights sold here on BPL, but three times lighter than the more mainstream but still lightweight Petzl Zipka headlamp. Its single LED is available in white or green, the former for bright, accurate light and the latter for preserving your night vision (great for fiddling with camera controls during night photography).
I'm afraid I've only used this in the mountains above 40° F, so I can't comment on cold-weather performance, but it's certainly bright enough for any conceivable in-camp task use, and is more than enough light for reading. The beam is fairly narrow but with a surprising throw...it's a task light, not a navigation light.
It weighs very little, fits anywhere, stores flat, and the ear clip also connects to rings, clips or gear lofts for top-down lighting in a tent. Adding a small strip of Velcro on the outside can allow it to be attached anywhere. :-) It's all plastic, so won't turn your ear to ice in the cold (and it fits under a tight earflap or beanie).
It gets a 4/5 because of on-the-ear comfort could definitely be better, it's not the world's sturdiest light, and its reliance on watch batteries for power. At the same time, all these factors still make it incredibly light and handy. I carry one as a and as a main light when car camping (how I often start the first night of a backpacking trip to acclaimate to the altitude) and as a backup to a Petzl Tikka in the backcountry...it's lighter than a set of spare Lithium AAA batteries. ;-) It also sits on my desk at home for crawling behind recalcitrant computers and for running wires through crawlspaces.
And since it's not marketed as Ultralight Camping Gear, it's reasonably priced: $12.95.