But the light output is pretty steady despite the varying current draw. Doesn't make sense to me either. After all, the voltage will drop over time during discharge too, so the power will drop even faster. Not a clue how that works. If anyone can explain it, I'd like to know. The only thing i can think of is a "burn in" of the LED as it was essentially new when the runtimes were done and some LEDs do have a forward voltage that drops as they "burn in". AFAIK lithium cells are born with all the capacity they are ever going to have and capacity drops from the date of manufacture - at least for the common lithium-cobalt chemistry which has higher capacity than most other lithium chemistries.
Hey, that's half the fun! 
Sorry I have thing for runtime, must be because I never had enough batteries when I was a kid and I appreciate things that run a long time.
Extremely professional review here brted, extremely informative and great shots. Frontpaged.
I decided to give them all some exercise, it was very, very bright in here last night.
I'll do a low runtime now. It'll probably be a day or so till it is done - it ought to run for 16-18 hours on low.
After 2 hours, output is now down 7%. Quite a long time to go.
Watched battery chargers are even slower than watched kettles - which, of course, never boil. And I have 10 more of them to charge.
Output now down to 86%. Quite a way to go.
Output now 82%. Still going strong.
78%. Not dropping appreciably. Got the 18650s all charged again.
Wow now that is pretty good.......
76% and going strong. There sure are going to be a lot of data points on the runtime graph.
76%
Down to 74% now. Wonder if it'll still be lit in 9 hours time when I get up in the morning?
72%. Off to bed so I'll stop boring you with updates till the morning when a runtime graph will appear. Assuming it has decided to turn off by then. I reckon another 3-5 hours should see it.
Long enough Mr. Admin? Or do I need to get some higher capacity cells?
Dude with higher capacity cells that light should last a year with low running...lol.
This has been a real white-knuckle thriller for me, percentages trickling in all day long, I love it!
24 hours or I'll eat my hat.
58% and still going. Better look out the hat seasonings!
We're now below 50% but it is still emitting light. I'll let it run till the cell protection cuts in. Now 47%
Still lit. Down to 29% Now 15,555 data points.
Looks like it'll still be lit when I go to work. It is just possible that hat eating won't be necessary.
Now down to 6%. Don't think I'm getting a whole day out of it.
How are you going to cook your hat?
Steamed....lol......with a little bbq sauce for good tasting. Thanks for doing the runtime....the light is still doing a good job at lighting up, have you tried turning the light off to see if it will come back on.