If you're reading this post, I'll ask you to consider your time and effort reading/responding to be charity work for the cause of education of a neophite. Thanks in advance.
Eneloop Pro NiMH cells have a capacity of ~2500 mAh and weigh 30g, a weight efficiency of about 83 mAh per gram. 18650 Li-ion's that I use aren't the most weight efficient for capacity (NCR18650GA), but have about 3500 mAh and weigh 48g, weight efficiency of 73 mAh per gram. By this measure, my AA Eneloops should allow flashlight designers to make lights that are more weight efficient by about 14%. Even if you choose 18650's that are more efficient, AA flashlights should at least be equally efficient at changing Amp-hours into lumen-hours.
But, when trying to find weight efficient AA flashlights, I've seen the exact opposite. A Zebralight SC600 can produce a 600-700 lm spot/flood for 74 minutes with a total weight of 112g. One of the most weight efficient AA lights I could find is the Eagletac GX25A3, which might produce slightly more lumens (a little over 700) for slightly less time (less than 65 minutes). Even granting that the light output from both lights is equally useful, and is a similar light output and duration, the Eagletac weighs 148g...empty! With 3xAA, it weighs 238g, more than DOUBLE the Zebralight weight.
I only give that single comparison as an example. I've tried a few other runtime and lumen combinations, with different types of lights, and seen very similar results--the AA lights are double (or more) the weight of their 18650 counterparts when you try to find equal light output and duration combinations.
Even at low outputs it seems true, even within a single (Zebralight) brand. Zebralight rates their SC63 at 160 lm for 12 hours, with a total weight of 112g. The Zebralight SC5 OP will put out 115 lumens (a bit less) for 3.5 hours (29% of 12 hours). That means, to be equally weight efficient as the SC63, even if we say that 160 lm approximately equals 115 lumens, the SC5 would need to weigh 32g including the battery (29% of the SC63 weight). At 88g, the SC5 OP is a featherweight, but crazily weight inefficient by comparison to the SC63.
So, what gives? I actually can't find a single lumen/time combination where any AA light beats 18650 lights. Why can't a flashlight designer build AA lights to be at least the same weight as their 18650 counterparts for a given lumen/time combination?
The theories I can imagine don't seem to add up to the large difference, but maybe they do. Let me know what I'm missing or underestimating:
1. flashlight structure of AA lights weighs more to hold multiple batteries, while 18650's can have fewer cells and therefore simpler/lighter structures
2. voltages of 18650's are more efficiently matched to today's LED and drivers
3. people are willing to pay big bucks for awesome 18650 lights, and consider AA lights to be "throwaway", so R&D money goes into 18650 lights and not into AA lights
4. consumers don't really care about weight efficiency, so designers just do what they have always done with respect to tube wall thicknesses, materials, heat sinks, design, and layout for AA lights.
5. I haven't found the "sweet spot" for efficient AA output/time
Eneloop Pro NiMH cells have a capacity of ~2500 mAh and weigh 30g, a weight efficiency of about 83 mAh per gram. 18650 Li-ion's that I use aren't the most weight efficient for capacity (NCR18650GA), but have about 3500 mAh and weigh 48g, weight efficiency of 73 mAh per gram. By this measure, my AA Eneloops should allow flashlight designers to make lights that are more weight efficient by about 14%. Even if you choose 18650's that are more efficient, AA flashlights should at least be equally efficient at changing Amp-hours into lumen-hours.
But, when trying to find weight efficient AA flashlights, I've seen the exact opposite. A Zebralight SC600 can produce a 600-700 lm spot/flood for 74 minutes with a total weight of 112g. One of the most weight efficient AA lights I could find is the Eagletac GX25A3, which might produce slightly more lumens (a little over 700) for slightly less time (less than 65 minutes). Even granting that the light output from both lights is equally useful, and is a similar light output and duration, the Eagletac weighs 148g...empty! With 3xAA, it weighs 238g, more than DOUBLE the Zebralight weight.
I only give that single comparison as an example. I've tried a few other runtime and lumen combinations, with different types of lights, and seen very similar results--the AA lights are double (or more) the weight of their 18650 counterparts when you try to find equal light output and duration combinations.
Even at low outputs it seems true, even within a single (Zebralight) brand. Zebralight rates their SC63 at 160 lm for 12 hours, with a total weight of 112g. The Zebralight SC5 OP will put out 115 lumens (a bit less) for 3.5 hours (29% of 12 hours). That means, to be equally weight efficient as the SC63, even if we say that 160 lm approximately equals 115 lumens, the SC5 would need to weigh 32g including the battery (29% of the SC63 weight). At 88g, the SC5 OP is a featherweight, but crazily weight inefficient by comparison to the SC63.
So, what gives? I actually can't find a single lumen/time combination where any AA light beats 18650 lights. Why can't a flashlight designer build AA lights to be at least the same weight as their 18650 counterparts for a given lumen/time combination?
The theories I can imagine don't seem to add up to the large difference, but maybe they do. Let me know what I'm missing or underestimating:
1. flashlight structure of AA lights weighs more to hold multiple batteries, while 18650's can have fewer cells and therefore simpler/lighter structures
2. voltages of 18650's are more efficiently matched to today's LED and drivers
3. people are willing to pay big bucks for awesome 18650 lights, and consider AA lights to be "throwaway", so R&D money goes into 18650 lights and not into AA lights
4. consumers don't really care about weight efficiency, so designers just do what they have always done with respect to tube wall thicknesses, materials, heat sinks, design, and layout for AA lights.
5. I haven't found the "sweet spot" for efficient AA output/time