# Why does every LED flashlight I use flicker and dim so much? **URL:** \ **Category:** Factual Questions\ **Created:** [December 19, 2017, 5:43am UTC](https://boards.straightdope.com/t/why-does-every-led-flashlight-i-use-flicker-and-dim-so-much/804842 "2017-12-19T05:43:40Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![swampspruce](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/swampspruce/32/261_2.png) [@swampspruce](https://boards.straightdope.com/u/swampspruce)\ **Post date:** [December 19, 2017, 3:04pm UTC](https://boards.straightdope.com/t/why-does-every-led-flashlight-i-use-flicker-and-dim-so-much/804842/21 "2017-12-19T15:04:36Z")
I’ve done the LED Maglite conversion for the 3D cell in SWMBO’s car and my 2 AA version at work; they are alright and the battery life is almost doubled, the beam throw is better too. Having said that, I also have a Klarus XT11 with an 18650 rechargeable and although it is roughly the same size as a AA Maglite, it is miles better in performance and if I use the lower settings, lasts much, much longer. I also have a Jetbeam 3m Pro w/ 2 18650 batteries for my car and it really lights the night up! I bought both on sale at [batteryjunction.com](http://batteryjunction.com) and did a fair bit of research on candlepower as well before \i bought. ---
**Author:** ![scr4](https://avatars.discourse-cdn.com/v4/letter/s/59ef9b/32.png) [@scr4](https://boards.straightdope.com/u/scr4)\ **Post date:** [December 19, 2017, 3:48pm UTC](https://boards.straightdope.com/t/why-does-every-led-flashlight-i-use-flicker-and-dim-so-much/804842/22 "2017-12-19T15:48:48Z")
LEDs are far more sensitive to overheating than incandescent bulbs. The incandescent bulb in a Maglite isn’t very different from the one in your oven. It doesn’t need any cooling. LEDs are semiconductors, and they degrade quickly if they are allowed to overheat. Each LED needs to be mounted to a heat sink with a thermally conductive compound. If this isn’t done correctly, it will have a short life. You even see this in commercial applications - LED traffic lights sometimes have a few LEDs out near the middle, which are more prone to overheating than the ones near the edge. Also, LEDs can’t just be connected to a voltage source. It needs to have the current limited, otherwise it will burn up and die. Good LED flashlights have current regulators, so the current through the LED is always within spec regardless of the voltage of the power supply. You could get away with just a resistor to limit current, but then it needs to be sized conservatively, to make sure the current is within spec even when the power voltage is as high as it can get (i.e. a brand new or fully charged battery). An unscrupulous LED manufacturer may use an undersized current limiting resistor which will increase the brightness but shorten the life of fthe LED. ---
**Author:** ![Mangetout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/mangetout/32/19_2.png) [@Mangetout](https://boards.straightdope.com/u/Mangetout)\ **Post date:** [December 19, 2017, 4:02pm UTC](https://boards.straightdope.com/t/why-does-every-led-flashlight-i-use-flicker-and-dim-so-much/804842/23 "2017-12-19T16:02:58Z")
> [@Face\_Intentionally\_Left\_Blank](#): > > You know, reading the reviews of the flashlights on Amazon, my issue seems to be a fairly common one. Ppl complain about the lights suddenly getting weaker for no discernible reason, they’d bang on it or change batteries to little effect, and then they’d give up and give it a bad review. > > Surely if this happens that much, the flashlight enthusiast community has noted this and maybe knows why it happens. IMO, consumer purchases of flashlights are not something people typically research before first purchase, because they are not perceived as complex devices. If you’re buying headphones, or a camera, or a smartphone, you want to know a lot about it before you buy, so you typically read reviews, watch an unboxing or two, etc, but a flashlight is just a light, right? So you just buy one that looks like it promises what you want within your budget, and are later disappointed. Reply gave a good summary of the technical reasons upthread; cheap lights use cheap components and don’t configure the product properly. The nature of LEDs anyway is such that they require a certain forward voltage before you get any light, so rather than dimming smoothly as battery voltage drops, they suddenly cut out when it drops below the threshold. ---
**Author:** ![am77494](https://avatars.discourse-cdn.com/v4/letter/a/d2c977/32.png) [@am77494](https://boards.straightdope.com/u/am77494)\ **Post date:** [December 19, 2017, 4:37pm UTC](https://boards.straightdope.com/t/why-does-every-led-flashlight-i-use-flicker-and-dim-so-much/804842/24 "2017-12-19T16:37:39Z")
Many times i’ve Resolved similar problems by spraying WD40 and cleaning out the battery contacts. YMMV ---
**Author:** ![DPRK](https://avatars.discourse-cdn.com/v4/letter/d/4491bb/32.png) [@DPRK](https://boards.straightdope.com/u/DPRK)\ **Post date:** [December 19, 2017, 5:49pm UTC](https://boards.straightdope.com/t/why-does-every-led-flashlight-i-use-flicker-and-dim-so-much/804842/25 "2017-12-19T17:49:33Z")
> [@am77494](#): > > Many times i’ve Resolved similar problems by spraying WD40 and cleaning out the battery contacts. YMMV WD40 has oil in it, though. I would use a bit of 2-propanol, unless the contacts are covered with rust or something. I agree it is worth checking that the batteries are reliably connected to the circuit and not jiggling around. ---
**Author:** ![nate](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/nate/32/13085_2.png) [@nate](https://boards.straightdope.com/u/nate)\ **Post date:** [December 19, 2017, 6:15pm UTC](https://boards.straightdope.com/t/why-does-every-led-flashlight-i-use-flicker-and-dim-so-much/804842/26 "2017-12-19T18:15:55Z")
I’m glad someone started this thread, as I’ve had the same experience as the OP. I’ve bought 3 LED headlights and after a battery change, each one is really bright for about 30 mins of runtime. After that, the brightness very noticeably drops off. One is a Coast, one is Energizer-branded, and the other I think is Ray-o-vac. It’s really annoying. Does anyone know of a good headlamp that doesn’t do this? ---
**Author:** ![swampspruce](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/swampspruce/32/261_2.png) [@swampspruce](https://boards.straightdope.com/u/swampspruce)\ **Post date:** [December 19, 2017, 6:56pm UTC](https://boards.straightdope.com/t/why-does-every-led-flashlight-i-use-flicker-and-dim-so-much/804842/27 "2017-12-19T18:56:23Z")
[Petzl](https://www.petzl.com/US/en/Sport/Lighting), [Black Diamond](http://www.blackdiamondequipment.com/en_CA/search?cgid=lighting), or [Fenix](https://www.fenixlighting.com/product-category/headlamps/) are all pretty good. ---
**Author:** ![kayaker](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/kayaker/32/441_2.png) [@kayaker](https://boards.straightdope.com/u/kayaker)\ **Post date:** [December 19, 2017, 6:59pm UTC](https://boards.straightdope.com/t/why-does-every-led-flashlight-i-use-flicker-and-dim-so-much/804842/28 "2017-12-19T18:59:42Z")
There is a two-for-Tuesday deal at [meh.com on LED Flashlights today](https://meh.com/). Can sell out at any time. ---
**Author:** ![Stranger\_On\_A\_Train](https://avatars.discourse-cdn.com/v4/letter/s/13edae/32.png) [@Stranger\_On\_A\_Train](https://boards.straightdope.com/u/Stranger_On_A_Train)\ **Post date:** [December 19, 2017, 7:04pm UTC](https://boards.straightdope.com/t/why-does-every-led-flashlight-i-use-flicker-and-dim-so-much/804842/29 "2017-12-19T19:04:53Z")
> [@Mangetout](#): > > IMO, consumer purchases of flashlights are not something people typically research before first purchase, because they are not perceived as complex devices. Leading to my self-ascribed law, “Any sufficiently mature technology is as simple to use as a flashlight.” > [@Mangetout](#): > > Reply gave a good summary of the technical reasons upthread; cheap lights use cheap components and don’t configure the product properly. The nature of LEDs anyway is such that they require a certain forward voltage before you get any light, so rather than dimming smoothly as battery voltage drops, they suddenly cut out when it drops below the threshold. This is absolutely the case. LEDs (light emitting diodes) have an optimal voltage where they perform at peak illuminating performance, and a threshold voltage below which it will perform inconsistently (flickering or varying in output) or not at all, as well as the thermal performance issues and damage mentioned above. Good LED flashlights, such as those made by SureFire, Streamlight, and Olight, actually have sophisticated power management systems which limited the supplied current and balance the circuit to maintain above the voltage threshold for the useful life of the battery. Cheap LED flashlights do not have sophisticated power management and may use poor quality LEDs and other components leading to poor performance and life. The o.p. does not indicate what brand of flashlights he has had experience with but does say that he uses “name brand alkaline batteries” which are presumably AA or AAA alkalines. It should be noted that alkaline batteries which are nominally rated at 1.5 V actually show a precipitous drop in voltage relatively early in their lifecycle, and drop to 1.2 V fairly quickly with sustained use. The batteries will “rebound” to a higher output after resting but will quickly drop back down to the reduced level, leading to marginal performance (flickering). Nickel metal hydride (NiMH, 1.2 V) and lithium (Li, 1.5 V) batteries have much flatter discharge curves and maintain a threshold voltage for much longer. See [URL=[BU-106: Advantages of Primary Batteries - Battery University](http://batteryuniversity.com/learn/article/primary_batteries)]this article from Battery University[/URL= for some more detail. Most good quality full-sized LED flashlights either use the 18650 recharchargable or A123 primary (non-rechargable) lithium ion cells. Although people complain about the costs of these cells, for a given output lifetime in high draw applications such as a flashlight and the long storage life they’re actually comparable or better than alkaline batteries. And spending ~$100 on one flashlight that works well is better than spending $20 every few months for one that works poorly or chews up alkaline batteries. You can find SureFire G2 or comparable polymer bodied flashlights on sale online for $60 to $70, and they’ll last for years of service in all kinds of conditions. Stranger ---
**Author:** ![jz78817](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jz78817/32/1028_2.png) [@jz78817](https://boards.straightdope.com/u/jz78817)\ **Post date:** [December 19, 2017, 7:11pm UTC](https://boards.straightdope.com/t/why-does-every-led-flashlight-i-use-flicker-and-dim-so-much/804842/30 "2017-12-19T19:11:51Z")
one other thing to consider is that LEDs will typically draw far less current from the battery for a given amount of light. if you have a tiny bit of corrosion on any electrical contacts, it may cause flickering and dimness due to poor contact whereas the higher current of an incandescent bulb might “break through” the corrosion/oxidation. also, incandescent bulbs take time to reach full brightness; even if there’s a brief momentary loss of electrical contact you might not notice it because the filament’s retained heat keeps it bright. LEDs turn on and off virtually instantaneously so any interruption is immediately noticeable. ---
**Author:** ![ZonexandScout](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zonexandscout/32/544_2.png) [@ZonexandScout](https://boards.straightdope.com/u/ZonexandScout)\ **Post date:** [December 19, 2017, 7:41pm UTC](https://boards.straightdope.com/t/why-does-every-led-flashlight-i-use-flicker-and-dim-so-much/804842/31 "2017-12-19T19:41:26Z")
(ahem…) Why is anyone banging on his/her flashlight? There’s nothing wrong that’s likely to be helped by banging on it. Change the batteries, clean the contacts, tighten the bulb (if it’s an incandescent with a removable bulb), but don’t just bang on it. If there’s an intermittent connection that momentarily reconnects when you bang on it, you need to get another flashlight. It will just fail you again when you most need it. Posted on Behalf of Flashlight Bangers Anonymous ---
**Author:** ![Face\_Intentionally\_Left\_Blank](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/face_intentionally_left_blank/32/288_2.png) [@Face\_Intentionally\_Left\_Blank](https://boards.straightdope.com/u/Face_Intentionally_Left_Blank)\ **Post date:** [December 19, 2017, 8:05pm UTC](https://boards.straightdope.com/t/why-does-every-led-flashlight-i-use-flicker-and-dim-so-much/804842/32 "2017-12-19T20:05:02Z")
> [@jz78817](#): > > one other thing to consider is that LEDs will typically draw far less current from the battery for a given amount of light. if you have a tiny bit of corrosion on any electrical contacts, it may cause flickering and dimness due to poor contact whereas the higher current of an incandescent bulb might “break through” the corrosion/oxidation. > > also, incandescent bulbs take time to reach full brightness; even if there’s a brief momentary loss of electrical contact you might not notice it because the filament’s retained heat keeps it bright. LEDs turn on and off virtually instantaneously so any interruption is immediately noticeable. But flashlights essentially use the same battery-retaining mechanism that any handheld battery device does. If this is the case, wouldn’t calculators and handheld video games suddenly fritz out and need turned off/on? Surely they would be more sensitive to dropped power than even an LED. ---
**Author:** ![Face\_Intentionally\_Left\_Blank](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/face_intentionally_left_blank/32/288_2.png) [@Face\_Intentionally\_Left\_Blank](https://boards.straightdope.com/u/Face_Intentionally_Left_Blank)\ **Post date:** [December 19, 2017, 8:21pm UTC](https://boards.straightdope.com/t/why-does-every-led-flashlight-i-use-flicker-and-dim-so-much/804842/33 "2017-12-19T20:21:03Z")
> [@Stranger\_On\_A\_Train](#): > > Leading to my self-ascribed law, “Any sufficiently mature technology is as simple to use as a flashlight.” > > This is absolutely the case. LEDs (light emitting diodes) have an optimal voltage where they perform at peak illuminating performance, and a threshold voltage below which it will perform inconsistently (flickering or varying in output) or not at all, as well as the thermal performance issues and damage mentioned above. Good LED flashlights, such as those made by SureFire, Streamlight, and Olight, actually have sophisticated power management systems which limited the supplied current and balance the circuit to maintain above the voltage threshold for the useful life of the battery. Cheap LED flashlights do not have sophisticated power management and may use poor quality LEDs and other components leading to poor performance and life. > > The o.p. does not indicate what brand of flashlights he has had experience with but does say that he uses “name brand alkaline batteries” which are presumably AA or AAA alkalines. It should be noted that alkaline batteries which are nominally rated at 1.5 V actually show a precipitous drop in voltage relatively early in their lifecycle, and drop to 1.2 V fairly quickly with sustained use. The batteries will “rebound” to a higher output after resting but will quickly drop back down to the reduced level, leading to marginal performance (flickering). Nickel metal hydride (NiMH, 1.2 V) and lithium (Li, 1.5 V) batteries have much flatter discharge curves and maintain a threshold voltage for much longer. See [URL=[BU-106: Advantages of Primary Batteries - Battery University](http://batteryuniversity.com/learn/article/primary_batteries)]this article from Battery University[/URL= for some more detail. Most good quality full-sized LED flashlights either use the 18650 recharchargable or A123 primary (non-rechargable) lithium ion cells. Although people complain about the costs of these cells, for a given output lifetime in high draw applications such as a flashlight and the long storage life they’re actually comparable or better than alkaline batteries. And spending ~$100 on one flashlight that works well is better than spending $20 every few months for one that works poorly or chews up alkaline batteries. You can find SureFire G2 or comparable polymer bodied flashlights on sale online for $60 to $70, and they’ll last for years of service in all kinds of conditions. > > Stranger Yeah, AA or AAA alkaline batteries. This may be the core of the problem. I think the battery voltage is dropping quickly under heavy drain, and the bulbs are not receiving the necessary volts, causing the dimming. This would lead me to believe that a change in battery tech might address the issue. Rechargeables, or lithium batteries, would probably fix much of the issue, with the rechargeables giving a flatter 1.2v output and the lithiums standing up to the heavy drain. If I get a flashlight specifically designed to use a rechargeable, it will probably not demonstrate this issue. Think I’ll get one that comes with a battery and can be charged without removing it. Such a flashlight should be able to handle 1.2v without dimming, and the batteries won’t drop in voltage significantly until they’re nearly discharged. Cheaper to operate than throwaway lithiums too. Thanks for the help, Stranger. And thanks to the others that have contributed links to read, links to flashlights they like, thoughts and ideas, etc. I’ll see if anyone has any more for us. ---
**Author:** ![Whiskey\_Dickens](https://avatars.discourse-cdn.com/v4/letter/w/9fc348/32.png) [@Whiskey\_Dickens](https://boards.straightdope.com/u/Whiskey_Dickens)\ **Post date:** [December 19, 2017, 9:31pm UTC](https://boards.straightdope.com/t/why-does-every-led-flashlight-i-use-flicker-and-dim-so-much/804842/34 "2017-12-19T21:31:50Z")
Regarding the rechargeable 18650 batteries, is there a flashlight that has a trickle-charging mode? I’m thinking I would leave my flashlight perpetually plugged in unless I was using it. The manuals I’ve looked at assume you will disconnect the flashlight when it is charged. I also suffer from the problem the OP is experiencing. I do have a Cree light with AAA’s but I probably replace the batteries every 4th-5th time I use the flashlight as I’m going a couple of weeks between each use. ---
**Author:** ![GusNSpot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gusnspot/32/436_2.png) [@GusNSpot](https://boards.straightdope.com/u/GusNSpot)\ **Post date:** [December 20, 2017, 1:10am UTC](https://boards.straightdope.com/t/why-does-every-led-flashlight-i-use-flicker-and-dim-so-much/804842/35 "2017-12-20T01:10:51Z")
How bad do you need a flashlight? If it quits, how much trouble are you in? If the answer is “A lot.” then you need to skip a few evenings out and get a good one and if you won’t have time to change batteries when it goes out, best to carry a spare. Lessons learned in a long life. Do not be penny wise and pound foolish. Especially if it can get you into do or die territory. Your Lumens May Vary ---
**Author:** ![Weisshund](https://avatars.discourse-cdn.com/v4/letter/w/ba8739/32.png) [@Weisshund](https://boards.straightdope.com/u/Weisshund)\ **Post date:** [December 20, 2017, 2:25am UTC](https://boards.straightdope.com/t/why-does-every-led-flashlight-i-use-flicker-and-dim-so-much/804842/36 "2017-12-20T02:25:33Z")
On cheap LED flashlights, this is usually because of the crappy on/off switch. Put a little finger pressure on it and watch. Sometimes also the contacts for the battery holder, but mostly for me, its the junk switches. ---
**Author:** ![GaryM](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/garym/32/241_2.png) [@GaryM](https://boards.straightdope.com/u/GaryM)\ **Post date:** [December 20, 2017, 2:27am UTC](https://boards.straightdope.com/t/why-does-every-led-flashlight-i-use-flicker-and-dim-so-much/804842/37 "2017-12-20T02:27:15Z")
> [@GusNSpot](#): > > How bad do you need a flashlight? > If it quits, how much trouble are you in? > If the answer is “A lot.” then you need to skip a few evenings out and get a good one and if you won’t have time to change batteries when it goes out, best to carry a spare. > > Lessons learned in a long life. Do not be penny wise and pound foolish. Especially if it can get you into do or die territory. > > Your Lumens May Vary Gus makes s good point. The amount of money you should spend on a light depends on how bad of you’ll be if it fails to work. If the light not working means I can’t find that can of beans, not to big a deal. No light means I can’t change that flat tire and make it home, I’m willing to spend some cash. I’ve lots of lights, most run on 18650 cells, but some can also run on CR123a cells as well. If I’m out where I may not be able to recharge I carry CR123a cells to use if my 18650 cell dies. GaryM ---
**Author:** ![swampspruce](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/swampspruce/32/261_2.png) [@swampspruce](https://boards.straightdope.com/u/swampspruce)\ **Post date:** [December 20, 2017, 3:03am UTC](https://boards.straightdope.com/t/why-does-every-led-flashlight-i-use-flicker-and-dim-so-much/804842/38 "2017-12-20T03:03:04Z")
This ---
**Author:** ![Fubaya](https://avatars.discourse-cdn.com/v4/letter/f/c2a13f/32.png) [@Fubaya](https://boards.straightdope.com/u/Fubaya)\ **Post date:** [December 20, 2017, 4:38am UTC](https://boards.straightdope.com/t/why-does-every-led-flashlight-i-use-flicker-and-dim-so-much/804842/39 "2017-12-20T04:38:21Z")
> [@Stranger\_On\_A\_Train](#): > > Leading to my self-ascribed law, “Any sufficiently mature technology is as simple to use as a flashlight.” You might have to change that if modern flashlights continue on their path of feature creep. It’s getting pretty hard to find a decent flashlight that isn’t laden with tacticool features. On and off, that’s what I want. I don’t need to cycle through a tactical map light, strobe disrupter, SOS signal and three levels of brightness every time I turn it on. ---
**Author:** ![GusNSpot](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/gusnspot/32/436_2.png) [@GusNSpot](https://boards.straightdope.com/u/GusNSpot)\ **Post date:** [December 20, 2017, 4:53am UTC](https://boards.straightdope.com/t/why-does-every-led-flashlight-i-use-flicker-and-dim-so-much/804842/40 "2017-12-20T04:53:42Z")
> [@Fubaya](#): > > You might have to change that if modern flashlights continue on their path of feature creep. It’s getting pretty hard to find a decent flashlight that isn’t laden with tacticool features. On and off, that’s what I want. I don’t need to cycle through a tactical map light, strobe disrupter, SOS signal and three levels of brightness every time I turn it on. Two of mine are the same, Olight M20 X WARRIOR. Has 3 brightness levels. Off/on brings it up in the last brightness you were using. Totally different switch for strobe. I am smart nuff to do my own SOS signal, if I am so bad I can’t do it or I am in a place or condition that it is a moot point, it won’t bring help in time. I leave it on ‘medium’ and if that is not what I want, I go up. So, one setting, ‘on & off’ works just like you say you want. YLMV 😃🆒😉 [Previous page](https://boards.straightdope.com/t/why-does-every-led-flashlight-i-use-flicker-and-dim-so-much/804842.md?page=1) [Next page](https://boards.straightdope.com/t/why-does-every-led-flashlight-i-use-flicker-and-dim-so-much/804842.md?page=3)