It is physics, the current protects the active zone from degradation
Watch this video
The picture before it plays shows the aging with current, the solid line shows longer life for 350mA, while the other for 100mA shows less for the same LED temperature, a DTP star keeps the LED a lot cooler than conventional cheap aluminum stars that are used in most application to save costs
There are tests that clearly show that if the LED keeps cool enough on the LED die a higher current makes in fact the LED age less than on lower current
LED ages from a process that is mainly rapidly increased at low currents like moonlight or low the LED can age 10 times faster than on full current
I watched this video multiple times
And I am native german, so I did understand well why low currents are far worse than heat to kill LEDs
The current protects the very thin active light emitting zone from electrically defective spots to migrate into it from the surrounding material, this active zone is a lot thinner than the rest so migration is a huge issue
Of course heat also increases the migration of electrically defective spots
On our CC moonlight flashlight the LED can age over 10 times faster than on max. rated current
You see the plot at 16:00 of the video
And that plot shows the LED running on 3% of its normal current
Our moonlights and firefliey modes on CC lights get below 0.1%
The odd thing is if we get good cooling an overdriven LED ages slower than at rated current when they got the same junction temperature
Pwm modes at LED nominal currents will be fine for lifetime
For XPL this means 0.35-3A on a cheap star if the junction stays within specification temperature limit
Basically the cooler it runs and the more current it gets the less it ages
Thanks for the video, I'll check it later, but I can say immediately something is wrong in "less current - less lifetime" logic,
if this is correct then worst case for LED lifetime is not to turn LED at all (leave it in reel for 1 year).
If 10x lifetime decrease at very low currents (0mA must be the worst by this logic) is true, then completely new,never used LED 1 year after production would be at the end of its life (1 year is ~8000hrs, 10x is ~80000hrs).
Your claim that "more current - less ageing" is completely wrong, you can check some L70 tests for various LEDs, at same Tj, LED at higher current ages faster.
This picture summarizes temperature and current effect on LED lifetime(btw check LED lumen output at 350mA - no drop at all after 100000 hrs):
In the Osram video they talk about a 350mA LED
At 100mA and 150dC it ages slower than on 10mA with 55dC, if you compare both pictures
So why do have Luxeon LEDs the opposite lifetime correlation?
Likely because at some point another factor comes in play.
Maybe thermal stress, who knows
In any case if you cool the LED better the lifetime gets rapidly better as well.
At very low currents the LED gets damaged by diffusion of defective spots in the active zone.
At zero current or close there is not enough energy present to move defective spots.
Even if he drives a XHP70 at 6V 7.2A with a DTP star he gets thousands hours to 70% brightness
If he drives a XHP70 at 50mA it will age probably as fast as with 7.2A
In flashlight use noone will probably see a significant degradation of brightness with a lot normal use
Nice! I’ve been on the fence about this mod ever since I noticed that one bank of leds is a tiny bit dimmer than the other two when in low mode.
It looks quite do-able and I love ramping on my other lights (Q8 and D4).
Any challenges or bumps in the road to look out for? How was it taking off the bezel to get at the emitters? Wasn’t there a warning from Astrolux about removing the bezel and damaging the leds?
So in other words making a moonlight with very low duty cycle PWM should increase LED life while the same moonlight with constant current will make it wear much more rapidly (altough with little more lumens per watt)…
I wonder if 20+ kHz range PWM can have any negative effect on LED though…
PWM increases the LED life in 2 ways the low current age is a lot less plus the LED is only 1/100 of the time on
so that would increase the lifetime by a couple hundred times at least
new version of MF01 needs to get a MCPCB modification as well
you can ignore the cables I put in there, basically you can wire it like you want, just make sure the red circles and the black circles are connected towards each other
the cables of me are in the 3 120° sections just different approaches
you cut so that 2 LEDs are together in series, while to board had originally 6 in series, so 2 cuts per 120° section
absolutely sure its 6S on the output of the driver
It wont be able to deliver Turbo much longer, the light pulls 120W from the cells and at like 30% discharge of the cells, it will fall out of Max brightness
The 2S driver can go to DD if the Buck regulator falls out of regulation while the boost driver gets more and more inefficient with dropping cell voltage and higher input current
Thanks! Freeme confirmed this as well. Really interesting development here. Ok I understand less cell voltage means more current is required for 120W with boost driver. But how how do you know the figures that with 30% discharge it will fall out of max brightness? Secondly, how many lumens would you loose? Just 5, or 25? Isn’t an actual test required to know these values?
I do know from my own ceiling bounce test using the M43 as a reference that with 3.75V for the 30Q in the MF01, I get less output (about 6000 lumens) than my M43. I’m curious then how many lumens the new boost driven MF01 will pump out… Output as a function of cell voltage is what I’m after.
Basically this new MF01 needs to be tested again. M43 can push turbo with cell voltage as low as about 3.5V with GAs (my own test), and the TM38 can push turbo with cell voltage as low as 3.3V TM28 4x XHP35 HI Review Video. New TM From Nightcore
Of course different settings, but we’re talking boost drivers here. Curious, curious, curious.
Seriously, if this new boost version can push 10000 Nichia lumens with cell voltage less than 3.7V, I’m probably getting it (again)! :sunglasses:
LED lifetime in ultra-low/moon mode is in any case academic. Whether very low constant current, or PWMed at much higher current.
They will last forever, in our usage.
People who need to understand the detail are making e.g. streetlamps or warehouse lighting that must last 25 years plus, on for maybe 12 hours/day on average in the northern latitudes, where I live. Cree e.g. provide copious data for professional engineers to deeply understand, run the LEDs at their most efficient current level (lumens/watt), understand how the silicone domes can degrade due to environmental contamination, even incorrect choice of e.g. o-ring seals than can outgass degrading chemicals, this is more and more a precisely understood engineering subject, and the likes of Cree etc. are continuing to refine their products for their real markets, which is not us.
Worry more about our over-driven turbo etc. modes, where heat and current density kills.We are usually pushing these things way beyond datasheet parameters.
Except for things like the MF01, where the extravagant use of e.g. 18 decent LEDs to kick out e.g. 10,000 lumens i.e. 555 per LED is very modest indeed. This is one of the last “mega torches” that I would have any concern about over-stressing the LEDs, assuming good thermal protection, which by reports it seems to have, maybe even over-cautious.
10 minutes in turbo getting the torch roasting hot (who knows what LED junction temperatures, upper limit is melting point of solder, where the none-lead stuff is better) might be equivalent to decades in moonlight.
Interesting to discuss, academically, but of no practical relevance, IMHO.
