Note the original poster said the PSK in question was very small - I would assume size is a significaint issue for this application.<br><br>For a extreme condition light (esp in 24hr dark) it would be understandable the selection would be different.<br><br>The other thought is that lithium batteries should work better in cold environments. <br><br>Of course small (coin type) cells just don't have enough juice in them (for primary lights in exterme conditions). They make both AA and D size lithium batteries, although the D cells are 3V so you would need to intermix a dummy battery (
http://www.hdssystems.com/ActionLightAccessories.htm#DummyBattery ) to get the correct voltage for most lights.<br><br>In regard to D cells working best, it isn't supprising -- an AA cell has 2,850 mAh in it where a D cell has 18,000! A coin cells like the CR2016 typically has under 90mAh.<br><br>The gotcha is the D cells output a lot of their power at very low voltages - a regulated light seems the optimal way to resolve this. Blackdiamond makes regulated headlamps, although they don't have any that take D cells directly (NxAA and rechargable). However, the regulated light advantage still applies with other alkalines like the AAs.<br><br>A light to check out for extreme use might be the ARC LS. Very sturdy, bright LED (similar to 10-14 "normal" LEDs), is regulated and takes a variety of battery configurations (1xAA, 2xAA, 1x123A).
http://store.yahoo.com/flashlight/arcls.html<br><br>Regarding single cell lights, I would submit that the current crop of single cell, LED lights like the ARC AAA and the CMG Ultra DO measure up. The ARC AAA and CMG Ultra are both as bright as a Photon II because they are (more or less) regulated lights.<br><br>Which of course dosen't mean you want to change a piston on your snowmobile in 24 hour darkness with one, but on the other hand, a full 17-25 hrs (CMG Ultra) of Photon class light when you don't have anything else is a big win IMO. And it's small enough to always live in your pocket, or tiny PSK. They are tough as nails and very reliable. <br><br>I'd be curious how the UK 2L would hold up to very cold conditions. It's quite a sturdy little light, VERY waterproof, runs on 2 x 123A cells and runs for 3 hrs. It's beam isn't great, but not horrible either. I'd certainly recommend it for almost any other emergency kit w/o question.<br><br>http://www.brightguy.com/detail.tpl?cart=103371491286155&sku=UND12005<br><br>-john<br><br><br>3V Lithium D cell:<br>http://www.hdssystems.com/LithiumBattery.htm