Photon Torch: At 7 grams this keychain light has to be about the lightest (adjustable beam) torch (4.5 lumens). Some models are also waterproof. The Maxell CR 2106 batteries for it can be bought from eBay for approx $5 for 10. Each pair lasts 12 hours, so that would be enough light for at least a ten days’ trip (at 6 hours per day) giving a total weight of approx 27 grams! You can use one CR2032 instead which last approx 2 ½ times longer. ($7 for 10 = 37 grams for 50 days!). The CR 2032 are 20mm in diameter and 3.2 mm thick – that’s how it works! The ‘necklace’ arrangement can double as a head torch. I often use it for this purpose, or you could make your own with a piece of very light cord and a micro cord lock. You can attach it eg to your hat with a Velcro dot. I always carry one as an emergency torch (in case my main one gives out, or I lose it!)http://www.photonlight.com/led-flashlights/photon-freedom-micro-led-keychain-flashlight/
