Greetings to all friends out there, i ve been a flashlight addict and collector during the past ten years in which i have purchased, used and experimented with 15 more or less flashlights. Most of them badget friendly like Convoy, Wurkoss etc but also a pricy Fenix as well with different emmiters including xml2, sst40, sft40, xhp50.2, xhp50.3, xpg2 and so on… In each and every case i have experienced a significant and PERMANENT maximum output drop after a few tenths of usage hours in the range of 10 to 20 per cent . To my understanding the hotter the emmiter the faster the occuring of the forsaid phenomenon. In the case of the sst40 i have also experienced a change in the color spectrum emmited over time.
Needless to say i am using as a reference the initial output of a cold body flashlight powered by a fully charged quality battery. Noteworthy also that my batteries are at the early stages of their life cycle and being charged strickly externaly on a smart charger. I take care of them as much as the rest of my gear. I never use turbo mode for more than 30 secs and in very rare cases did the safety power drop feature actually kicked in.
I understand best way to back up my observation would be to use precise equipment (which i have not) and relate luminance and intesity measurements of an emmiter both at the start of its life out of the box and lets say 50 hours of usage later. I only got my visual perception on the same phenomenon in many different occasions under the same light conditions . Especially when it comes to intensity i believe its unquestionable since when the emmiter was out of the box i used to perform the " burning black paper trick " but not being able to repeat it later.
Seems kind of strange to me that after hundreds of youtube reviews i have watched even by amateurs and hundreds of written articles never have i came across a reference that justifies my observation. Did anybody out there have a similar experience in the past and even better can he provide technical explanation on that ? Please share…In case there has allready been a discussion in the blf forum under my radar please excuse the waist of space and time.
Looks at flashlight reviews by ZeroAir and 1Lumen, which all include runtime graphs that clearly demonstrate the stepdown phenomenon. It happens for a combination of reasons, including:
(1) Programmed/intentional stepdown by the driver because if the maximum output is sustained indefinitely, the equilibrium surface temp of flashlight will burn your skin, and
(2) Voltage sag in the battery and resistances within the circuitry drops the amount of current that the battery could supply.
This strikes me as very strange–noticeable degradation of the emitter over the course of a few tenths of hours, i.e., on the order of tens of minutes? Perhaps the heatsinking is inadequate, due to various factors from poor soldering/reflow to improperly applied thermal paste. Or the emitter is overdriven too far beyond its comfort range.
Is it a situation where you tested for max output of a light when you first have it, and then could never get the same output level again?
I have observed anecdotally in some of my lights the same phenomenon and have always been puzzled by it. But as an amateur with limited number of lights, batteries, and amateur grade measuring devices, I never could rule out other variables such as battery decay, measuring errors, and never knew what to make of it for sure.
At any rate, I think this process is referred to as light decay, lumen decay/depreciation, luminous flux decay, etc., and yes in LEDs. I am of course no expert, but from googling I believe one of the main reasons is heat’s damaging effect on the LED itself. Other factors include quality control (not all LEDs created to same quality), humidity, damage to power supply circuit, etc. The only question I still have though, is if this is supposed to be a slow process over thousands of hours only, or could it happen quickly (as in after a year of Turbo output and extreme heat “abuse”) as well.
This is interesting–most manufacturers rate 10000+ hours till 70% output, and AFAIK nobody has quantified just how much this process is accelerated by suboptimal operating conditions.
I’ve seen lots of Convoy S21D/S21Fs with burnt-out 519A’s, and other modes of failure with other emitters. I’ve even damaged a 519A myself with excess heat during reflow–up to 500mA or so the LED is normal, but above that the phosphor immediately saturates and makes a dim blue-green beam.
There is evidence to suggest that certain budget lights are way overdriving the emitters (519A especially due to its low Vf and tendency to be paired with 5A drivers that output significantly more than 5A). The overdriving may be happening to such extent that a lower current would actually result in more output, and it would be unsurprising to see much faster damage from overdriving past peak output.
Everything dies.
The shiny new thing is not as shiny on the second day.
Totally shocking there’s a ‘burn-in’ effect.
Heat is the enemy! I want a cryo- flashlight.
Seriously, don’t push too hard, it’ll last longer.
Live fast, die young- o mighty lantern, thou warst valiant in battle!
I any reasonably well designed flashlight (aluminium shelf, copper MCPCB, thermal paste, proper contact, sane driving levels, temperature control) this is not going to happen.
You won’t be able to see any degradation after 50h when the manufacturer states 50.000h to 50% - it will take much much longer.
Interesting question! One interesting point of comparison would be capacity of batteries, which drops off roughly exponentially as a function of the number of cycles. However, since the later cycles are shorter due to the reduced capacity, the capacity drop-off, as a function of usage time, actually ends up being roughly linear.
I see, thank you for clarifying! I think the most probable issues are (i) overdriving and (ii) overheating. The latter happens a lot with poor quality control, but it shouldn’t happen to all of your lights. Do you use the maximum output a lot (e.g., leaving maximum on continuously for minutes) on all of your lights? Or do you mostly use lower modes and occasionally use maximum?
If this phenomenon is universal and has simply gone unnoticed (which is possible since many of us upgrade to the newest emitters as soon as they are released), it definitely merits more discussion.
Seems you ve got it right and at first i blaimed my budged friendly choises. Then i happened again in a even worst way to a xml2 1000 lumen Fenix edc with triple the cost of a equivalent Convoy…
A sample size of n=2 is by far not large enough to make general conclusions. You had - probably - just bad luck.
I’ve never seen any noticeable degradation on any of my led lights. Well, except one with a 365nm UV LED that wasn’t properly heat-sinked and it killed itself on turbo in about 20 seconds.
Since i notice the recurring of the phenomenon to all my flashlights i strickly purchase flashlights with momentary mode for short turbos, this only buys me a few more hours of the out of the box experience untill the inevitable decay.
Noticeable emitter degradation after 50 hours of operation is not normal, which is why nobody’s talking about it.
I’ve seen that sort of thing happen when an LED is driven really hard without an adequate thermal path, but it’s surprising to hear about it happening with multiple units from reputable brands.
