Review of Fenix TK41, with measurements and outdoor beamshots

[candle lamp]

Each bank is 4 cell in series, this increases voltage but keeps current the same.
With banks in parallel the voltage stays the same, but the current increases.

A simple example with two cells, each 1.2 volt 2000mAh:
In series: 2.4 volt, 2000 mAh
In parallel: 1.2 volt, 4000 mAh



And again: The light does not draw 2.8 ampere all the time, but more like 2.2 ampere in average.

Therefore Is the input voltage totally 4.8V (4000mAh capacity) in case of using Eneloop Ni-Mhs?

Do we call it 4S2P?

Thanks for your answer to my previous question.

Best regards,

 

[HKJ]

Therefore Is the input voltage totally 4.8V (4000mAh capacity) in case of using Eneloop Ni-Mhs?

Yes. Just remember that NiMH has a nominal voltage of 1.2 volt, a freshly charger NiMH is above 1.4 volt.

Do we call it 4S2P?

Exactly.

 

[candle lamp]

Thanks a lot for your time. HKJ

One more question please.

How about the batterires connection for TK40, TK45?

Are the both lights 8 cells in series(=8S)?

I could get the above assumption from your TK45 review's table.

 

[HKJ]

How about the batterires connection for TK40, TK45?

Are the both lights 8 cells in series(=8S)?

TK40: 4S2P
TK45: 8S

 

[Sharpy_swe]

As always :goodjob:

Your reviews are always top notch!

 

[Sunflash]

As always :goodjob:

Your reviews are always top notch!

+1
good job.

 

[bbb74]

Thankyou for the review. Out of curiosity I was looking at the cree xm-l specs.

The XM-L maxes out at a max of 3A and a forward voltage of ~3.35V = ~10 watts. Your graphs show the TK41 maxing out around the ~10.5 to 11 watts mark, so after subtracting driver loss, it appears the led is being driven at about 100%.

Note Cree say: "Cree currently recommends a maximum drive current of 1500 mA for XLamp XM-L white in designs seeking the ENERGY
STAR* 35,000 hour lifetime rating (≥ 94.1% luminous flux @ 6000 hours) or 25,000-hour lifetime rating (≥ 91.8%
luminous flux @ 6000 hours)."

Cree also say that at 3A, the XM-L will be at 325% of the rated luminous flux (which is 280-300 lumens @ 700mA for the T6 bin) so 910 to 975 lumens at 3A. Given that Fenix say 800 lumens for the TK41 does that sound right? Only a ~15% drop in output from emitter lumens to ansi lumens??

Again must be something wrong with my maths... but maybe not as xm-l peak out a touch above 1000 lumens with a U2 bin?

 

[HKJ]

Note Cree say: "Cree currently recommends a maximum drive current of 1500 mA for XLamp XM-L white in designs seeking the ENERGY
STAR* 35,000 hour lifetime rating (≥ 94.1% luminous flux @ 6000 hours) or 25,000-hour lifetime rating (≥ 91.8%
luminous flux @ 6000 hours)."

Flashlights are not designed for energy star ratings.

Cree also say that at 3A, the XM-L will be at 325% of the rated luminous flux (which is 280-300 lumens @ 700mA for the T6 bin) so 910 to 975 lumens at 3A. Given that Fenix say 800 lumens for the TK41 does that sound right? Only a ~15% drop in output from emitter lumens to ansi lumens??

You calculations looks fine to me and I agree with you that a getting 85% of the light out the front is a very impressive feat (If they use the T6 bin).
Fenix might not even drive the light at 3A, if you look at my voltage sweep, it peeks at 2.8A. This does not have to be the led current, but probably it is.

 

[bbb74]

Flashlights are not designed for energy star ratings.

I know I know, but am wondering how long a tk41 will actually last if its always in turbo. I'm thinking of getting one but would hate the guilty feeling when going exploring for a few hours in turbo

You calculations looks fine to me and I agree with you that a getting 85% of the light out the front is a very impressive feat (If they use the T6 bin).
Fenix might not even drive the light at 3A, if you look at my voltage sweep, it peeks at 2.8A. This does not have to be the led current, but probably it is.

That 2.8A was at a voltage of about 3.7v or something though right, so at the xm-l's max forward voltage of 3.35v the current could be around 3A?

 

[DavidD]

I read that the lux of the TK41 on Turbo is approximately 55,000. I am wondering how that transfers down to the lower levels. Is the formula linear (cross multiply & divide) or is there a different formula?

Does 55,000 @ 800 Turbo translate to:
23,031 @ 335 High? (335*55,000/800)
7,425 @ 108 Medium? (108*55,000/800)
688 @ 10 Low? (10*55,000/800)

For those familiar with the Streamlight ProPolymer Luxeon 4AA, I believe it was about 3,000 lux @ 42 lumens, give or take - and considered a good thrower at those levels. Adding in 1 more comparison to the above list...

2,888 @ 42 ProPoly Level (42*55,000/800)

Does this indicate that it is about the same degree of thrower as the ProPoly (just able to go a WHOLE lot brighter)?

-- just trying to get a handle on the throw at the lower levels...
David

 

[HKJ]

I read that the lux of the TK41 on Turbo is approximately 55,000. I am wondering how that transfers down to the lower levels. Is the formula linear (cross multiply & divide) or is there a different formula?

Does 55,000 @ 800 Turbo translate to:
23,031 @ 335 High? (335*55,000/800)
7,425 @ 108 Medium? (108*55,000/800)
688 @ 10 Low? (10*55,000/800)

That is correct.

For those familiar with the Streamlight ProPolymer Luxeon 4AA, I believe it was about 3,000 lux @ 42 lumens, give or take - and considered a good thrower at those levels. Adding in 1 more comparison to the above list...

2,888 @ 42 ProPoly Level (42*55,000/800)

Does this indicate that it is about the same degree of thrower as the ProPoly (just able to go a WHOLE lot brighter)?

Not really, there are many beam shapes that will have the same lux at the same lumen level. You can have a very small hotspot and lot of flood or you can have a large hotspot with no flood and anything in between.
i.e. due to the higher lux the TK41 will throw much further than the ProPolymer, but does not necessary have the same beam shape.

 

[ScaryFatKidGT]

Like the beam shots THX! wish you would of put in a TK35. Is the LD40 really that dull? and the TK45 is all flood?

 

[HKJ]

wish you would of put in a TK35. Is the LD40 really that dull? and the TK45 is all flood?

Just click on the picture with all the lights and you will get many more beamshots that includes a TK35.
The LD40 is not dull, but it is less than half the lumen of the TK40/TK41/TK45 lights. TK45 is not all flood, but it is much more flood than than TK41.

 

[AMD64Blondie]

Great.. I already own a TK40 and now you're tempting me again? Sigh...

 

[burpee]

I really love all the great information posted here. And I'm about to pull the trigger on a TK41 purchase. But I'd like to hear whether someone who has already collected many remarkable torches whether I should just go ahead and make the move into flashlights using protected 18650 cells. I already own 40 or fifty AA NiMH cells and various chargers.

How many of you have 2x18650 torches that have nearly the throw of the TK41? Can I get a torch, charger and cells for about $150 US? Don't mean to warp the thread, just asking?

 

[Fern]

Hi HKJ and thanks for the review.

I recently purchased a TK41 and have a question regarding the beam profile.

My sample has a dark area where the hot spot should be which is encircled by a very bright ring before transitioning into the corona/spill.

This is ONLY noticeable beyond a distance of 4-5 meters. Any distance under that and the hot spot looks a normal solid white.

Here's a link to a video clip I took showing the effect:

http://www.mediafire.com/?qmc2mi2tpha07y2

This beam shot was taken at 20 meters.

Please note that the dark hot spot/bright ring effect was difficult to capture on camera and is much more apparent and obvious to the naked eye.

Does your TK41 sample exhibit this beam pattern?

I would like to establish if this is typical or if I have a defective unit. I have emailed Fenix but have received no response yet.

Feedback appreciated from any other TK41 owners.

 

[trooplewis]

No donut hole in my hotspot, but my emitter is off-center and that may be why.

 

[Fern]

Hi trooplewis thanks for responding.

My emitter is perfectly centered and so is my donut hole :shakehead

What distance have you checked your beam? As I mentioned this artifact only shows up at ranges exceeding 4-5 meters, and is very obvious even against targets such as foliage, textured surfaces etc. Definitely noticeable against a smooth wall.

 

[Red-T]

My TK41 shows a similar pattern: very close (around 10 cm) a dark clover-shaped center, beyond that fairly smooth. At larger distances the hotspot has a more yellowish center with a brighter and bluish outer ring.

 

[burpee]

This beam shot was taken at 20 meters.
Please note that the dark hot spot/bright ring effect was difficult to capture on camera and is much more apparent and obvious to the naked eye.
Does your TK41 sample exhibit this beam pattern?
I would like to establish if this is typical or if I have a defective unit. I have emailed Fenix but have received no response yet.
Feedback appreciated from any other TK41 owners.

I just received my TK41 yesterday and by no means any expert. However, I can tell you that I do indeed see the "center hole" effect, although I couldn't see it in your video.
My TK41 emitter is perfectly centered any for anyone FYI - perfect switch operation every click.
I pointed my TK41 at a white wall 3 or 4 meters and at first glance did not notice the "hole effect." As I moved forward and away from the wall I can see the "center hole" effect appear and disappear in the hot spot. This lightening and dimming of the center of the hot spot is most definitely observable. Its not all illusion.

I doubt this pattern can be described as a defect. Like yourself, I guess the next thing I would want to do is have some one else stand beside me and substantiate the changing nature of the hotspot in conjunction with my own perception. In addition, I wonder if the color of the wall or other factors will amplify or cancel this effect.

Hey I reviewed your video again - and now I see the effect - could you try holding the hotspot steady on the door and walk toward and then away -I think you'll see the "change" I describe.