Two O-rings, a micro cord lock and a short length of 1mm Dyneema transforms this 9 gram wonder into an 11 gram wonder. At 45 lumens for 1 hour or 1 lumen for 48 hours (or anywhere else in between) this Nitecore Tube Light is a wonderful torch. The 1 lumen setting is quite adequate for reading of a night (if you still use books) or for finding your way around in the dark once your eyes are adjusted.
These little guys weigh less than the AA battery used to power most ultralight torches (such as this excellent example: http://www.theultralighthiker.com/mini-super-torch-a-weeks-light-weighs-50-grams/) so it is well worth carrying a couple in your pack especially if you have the means of recharging them (such as this: http://www.theultralighthiker.com/charging/) or this: http://www.theultralighthiker.com/powerfilm-usb-aa-solar-charger/
PS The onboard lithium battery is approx 100 milliamp hours (printed on the battery).
For those who cannot resist tinkering, there is a mod which will produce 73 lumens from this torch: https://www.reddit.com/r/flashlight/comments/3m13l8/how_to_hotrod_a_nitecore_tube/