I have some questions and I would like your help. I see that many AA flashlights reduce their brightness after 1 or 2 minutes. why this happens? it’s for preventing overheating or a way to extend the battery life? Also if a flashlight reduces its brightness after 1 minute and i close and open it again after 5 minutes, will it returns to its maximun brightness?
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Excellent question.
It steps down due to heat. If it did not do this, it would be dangerous. You can trick it by turning it on and off but that is not a convenient way to operate a light.
I would not worry too much about an AA light. Its only really an issue in more powerful lights.
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It depends on the design. Some good design will only have the output limited by heat. Most will have a timed step down that reduces brightness regardless of the heat. In latter case, you can keep turning off and back on the light to restore full output but it will drain battery fast, and possibly overheat the LED or electronics.
And there is a darker side to this. If a light gives 1000lm for 1 minute, automatically step down to 300lm and run for 3 hours, the manufacturer can advertise the light as having 1000lm for 3 hours. It’s a lie but most consumers can’t be bothered to check the actual runtime graph so the number sells. Not all reviewers check the full length run. Many just turn on the light and say ‘Wow bright’ then quote manufacturer numbers and concludes that this is a very impressive light that gives this much light for over 3 hours! Infact the step down is just enough for them to finish their review!
The verdict? Always check runtime graphs.
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So its very important for a flashlight to be efficient and have stable output for a long time. According to the above i would like to suggest me a tail switch 14500 AA flashlight with stable output and good rutimes. I dont care about having the biggest output. I was looking about the Skillhunt E2A but i see from the runtime graphs that its is not very efficient.
TAC AA EDC Flashlight|AceBeam® Official Store | Flashlights, Tactical Lights
or
E05 II 1300 Lumens High Output EDC Flashlight - Mankerlight Official
There are many others but these are my two favorites.
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The TAC AA does not have constant output with Li-ion battery, only with NiMH – and all of them use PWM for dimming!
The E05 II is much better in my opinion, in every detail (except the LED color and CRI). Review and comparison coming in a few weeks.
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I suggest Convoy T3 or T5–they are not the brightest or smallest but they have stable output and various LED options.
After a reasearch i see that Convoy T3 has very regulated output and it is a good choice for tail switch. I need somthing around 5000k and i think about 519a 5700 version. Whats the differnce with the T5?
T5 has a TIR lens and is shorter. Should be the same apart from that.
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A 30 second burst is sometime useful, but its always useful to check the charts, lots of lights have max and high modes that after the burst are dimmer than their med modes after a couple minutes. I usually focus on how the light performs in the 100-150lm mode.
Here are two reviews with runtime graphs of the Convoy T3. Note that both reviews are using relatively low capacity LiIon batteries. New tech Vapcells are 1250mAh. Double the capacity of the efest purple in 1Lumens review, so expect longer runtimes with higher capacity batteries.
Compare that to a ReyLight Lanapple, which I like for its true Moonlight, programmability, and dual fuel capability. It does OK on LiIon, but on NiMh in this review it does not have a mode that can sustain over 60lm 
Note: Different reviews have different results for ReyLights and I think there have been driver changes.