Black Diamond Gizmo 20 79g 3 24/?/4 20/?/100 25/?/5 2AAA
Petzl Tikkina 2 19 80g 2 23/10 55/190 23/13 3AAA
Coleman Axis 15 ? 2 33/13 25/66 26/16 3AAA
Coleman Axis HP 20 ? 3 75/43/15 11/20/55 43/31/10 3AAA
The brightest of the bunch is the Coleman.
What's the more efficient light, with more light for longer run time? Is there any way to compare these lights for efficiency? Can they be ranked in terms of "lumens-hours"?
Petzl Tikkina 2: high 20lm x 55hr = 1100 lm-hrs, low: 10lm x 190 hr = 1900 lm-hrs
Coleman HP: med 43lm x 20hr = 860 lm-hrs, low: 15 lm x 55 hr = 825 lm-hrs
Black Diamond Gizmo high: 24 lm x 20 hrs = 480 lm-hrs
I used to feel that way (and still do to a degree) but there are a couple of positive aspects. They generally result in a light that is flatter (closer to the head) than would be the case with AA's. Three AAA's weigh less than 2 AA's and if the light is being used with alkaline batteries at least on high there will be sag. With 3 batteries that load is shared and the resulting sag is less.
On the other hand, 4 AAA batteries cost as much as 4 AA batteries but 4 AA batteries have twice the capacity of 4 AAA batteries. When using expensive lithium batteries it's even more of a factor.
I do think with a good design 2 AA's can be utilized in a small headlamp and using lithium would reduce the weight (but not the size).
I now see both sides of the issue rather than only one side I guess.
They are definitely not outputting the max rated lumens. The standard test is to turn the light on in whatever mode is being advertised (max, min or whatever) and letting it run until it gets down to .25 lux at 2 meters. That's considered to be the equivalent of moonlight (lower than that is not considered to be useful).
This doesn't really tell anyone anything however. Some lights are regulated, some are regulated for a short while and then fall out of regulation, and some are unregulated. It's hard to compare lights under those circumstances.
If you can figure out what emitters each light is using you can just compare the figures from the spec sheets for those emitter and get a rough feeling for efficiency.
The run times are more meaningful in my opinion if you typically use a light on low. If you are using it anywhere near high then those run times are meaningless. You're not going to get more than a few hours from any of them on high anyway.