How long, how bright on AA batteries

Recently a picked up a Pelican 2AA light with a 178 lumen high and a 4 hour run time.
http://www.candlepowerforums.com/vb...-178-lumen-(2360-based)-10-with-free-shipping

The specs got me thinking about the claimed specs on many lights. Particularly how long and how bright a light can be. The FL1 specs of course would allow a light to be very bright for just a minute (say 1000 lumens) then drop down to something stupidly low (say 10 lumens) for literally days of run time. Thus we would have a spec of 1000 lumens, 48 hours on high.

So my question is how bright, how long should we expect on a given battery type with no significant reduction in brightness? I know this isn't an exact number as the efficiency of the LEDs and battery capacities change with type, current etc. Still, a while back I had a 111 lumen Energizer elmcl21l light. It had a 1 hour run time on 2 alkaline AAs. It was well regulated and based on what I recall of reviews it didn't dim. These days we see 2AA lights claiming near 300 lumens and run times that are 2-4 hours at full power. I'm sure LEDs are more efficient now but not that much better. So how long/bright can a 2AA light go? Are there any contemporary 2AA lights that don't dim from their high setting?

BTW, I do think there is a practical justification for having a high (turbo) type mode that the light couldn't sustain. Sometimes you do want lots of light for just a short time. Still, when I'm told that a new 2AA light has a high setting of 245 lumens and a 2.25 hour (call it 550 lumen*hours) run time.... well I just don't believe that the new LEDs are that much better than the ones from 6 years back (111 lumen*hours)

How much should a 2AA light output for an hour or two with no drop in brightness (flat regulation)?

See how well selfbuilt's 2AA round-up review answers your question
http://www.candlepowerforums.com/vb...d-up-Review-(D25C-D25A2-D25LC2-XM-L-amp-XP-G)

If you want no drop in brightness for a long time, just start at a lower brightness that the AA can support. They do Ok with low draw applications, so, make it low enough, use flat regulation, and you can run for months at a constant brightness.



After that, its about what the LED puts out at a given draw...and how to get the batteries to support it at a useable output/runtime.

Look at a smoke detector or wall clock that use AA for example...they run a LONG time.

nitedrive said:

Recently a picked up a Pelican 2AA light with a 178 lumen high and a 4 hour run time. ...
How much should a 2AA light output for an hour or two with no drop in brightness (flat regulation)?

Click to expand...

Congrats!
Lumen claims are misleading. You wont get 178 lumens on high for 4 hours. Marketing has succeeded in confusing you.
long run times are at low lumens, dont be misled by the lumen specs, look at the actual runtime charts below, notice what a HUGE difference battery type makes

The best way to get the most out of your light is to Not use Alkalines.

Poppy said:

See how well selfbuilt's 2AA round-up review answers your question
http://www.candlepowerforums.com/vb...d-up-Review-(D25C-D25A2-D25LC2-XM-L-amp-XP-G)

Click to expand...

from that great link, on the chart below:

Fenix LD20 (Turbo, see blue line that starts at 100), has a 180 lumen high, close to yours, will operate on Turbo for 40 minutes on Alkalines (first line in the legend box),
at which point it will have dropped to 90 lumens (50% of its 180 high). This is totally normal.


In the above Alkaline chart, the blue line near 50 is Medium instead of Turbo, it starts out at about 90 lumens, and holds steady for 2 hours and 25 minutes.

Summary, a light rated for 180 lumens goes 40 minutes on maximum before dropping to 90 lumens
the same light on medium, starting at 90 lumens, lasts 145 minutes before dropping below 90 lumens.

Now Eneloop,
Fenix LD20 goes 1 hour and 27 minutes, to drop to 90 lumens.
The runtime on Eneloop is DOUBLE that of Alkaline.
Eneloop has a much flatter discharge curve also, it holds steady for a lot longer, see the flat lines below:

TEEJ said:

If you want no drop in brightness for a long time, just start at a lower brightness that the AA can support.

Click to expand...

great point, agreed, the higher it starts, the harder it falls
two AA seems to support 90 lumens (I wish selfbuilt listed actual lumens in his charts)

Poppy said:

See how well selfbuilt's 2AA round-up review answers your question
http://www.candlepowerforums.com/vb...d-up-Review-(D25C-D25A2-D25LC2-XM-L-amp-XP-G)

Click to expand...

Thanks! Those run time plots are exactly what I wanted to see. The Eagletac 2AA when running for about 1 hour at constant brightness was ~150 lumens for 50 minutes (125 lumen*hours). That would make sense. It puts the new stuff as more efficient but not much more than the LEDs from about 6 years back (I don't have exact numbers for that old light). It also answers my question, more than perhaps 140 lumens and you have to figure a 2AA light will drop output to last more than 1 hour. Of course a lower output will last longer and a higher output without drop will kill the battery faster. If a light claims 4 hours on high with 2AAs then I can assume it's actually doing most of that run at less than 100 lumens. It also goes without saying that the capacity of the battery is dependent on discharge rate. One of the reasons why I actually care about this is because I rarely actually run a light from full to dead. Most of the time I'm going to run in short bursts. Well a light that starts bring then really drops to get a long run time may have rather short run time if you only use it 10 minutes at a time. Thus something that claims say 4 hours on high would deliver more like 1 hour cumulative if the use pattern was intermittent (ie 100% for the 10 minutes then off then 100% for another 10 minutes). That use subjects the light to only the high current part of the run time and thus it wouldn't last close to 4 hours.

Anyway, thanks for the info!

nitedrive said:

The FL1 specs of course would allow a light to be very bright for just a minute (say 1000 lumens) then drop down to something stupidly low (say 10 lumens) for literally days of run time. Thus we would have a spec of 1000 lumens, 48 hours on high.

Click to expand...

Incorrect. FL1 runtime rating is time in minutes until the light output drops to 10% of its original value (measured 30 seconds after turning the light on). So runtime at 1000 lumens would be until output drops to 100 lumens.

Yamabushi said:

Incorrect. FL1 runtime rating is time in minutes until the light output drops to 10% of its original value (measured 30 seconds after turning the light on). So runtime at 1000 lumens would be until output drops to 100 lumens.

Click to expand...

Sorry, yes, you are correct, 10% thus 101 lumens. I do actually know this but forgot it for my example.