Fenix TK35UE (MT-G2, 2x18650, 4xCR123A) Review: BEAMSHOTS, RUNTIME, VIDEO+

Swedpat

Flashlight Enthusiast
Joined
Jan 5, 2008
Messages
3,448
Location
Boden, Sweden
Consequently TK35UE would be a great between complement to Wildcat and TN35. And when I read your runtime graphs and compare to TN35 it seems that TK35UE actually is more efficient than TN35: if I calculate correct lumen-hours are higher compared to the number of cells. And that despite TN35 much more massive head will make a better heat dissipation. Not a big issue anyway, but having three MT-G2 lights in the collection isn't that bad...
 

selfbuilt

Flashaholic
Joined
May 27, 2006
Messages
6,936
Location
Canada
And when I read your runtime graphs and compare to TN35 it seems that TK35UE actually is more efficient than TN35: if I calculate correct lumen-hours are higher compared to the number of cells.
One comment there - my relative output scale (on the graphs) is not the same as lumens. My estimated lumen scale is based on the power relationship coversion of raw lightbox output. So you would need restate the runtime graphs in estimated lumens (at least approximately) in order to do a true lumen-hours comparison.

All that said, my TK35UE is indeed an unusually good performer for a MT-G2 light. :whistle:
 

MichaelW

Flashlight Enthusiast
Joined
Dec 8, 2007
Messages
1,789
Location
USA
Actually, it's even simpler than that. The step-down from Turbo actually resets the level to Hi. So in order to get back to Turbo, you just need to press the mode select once (i.e., it jumps right back to Turbo on a single press). :)
Ah, I see.
But how many presses will it take before the 'Over-heat protection' decides to veto your vote?
 

selfbuilt

Flashaholic
Joined
May 27, 2006
Messages
6,936
Location
Canada
But how many presses will it take before the 'Over-heat protection' decides to veto your vote?
Hard to say, but I would expect it's a reasonable one.

I have gone and done repeated re-starts every 5 mins on Turbo (below) - but these were all done under a cooling fan, and giving the light a few mins to cool before re-starting. I've edited out the pauses to better show what to expect (the spikes show the time I shut-down). I've also plotted it on my estimated lumen scale, for better resolution.

TK35UE-Restart.gif


As you can see, the light seems to be largely direct-drive on Turbo, eventually dropping to the Hi level around the time that the batteries are nearly exhausted.

Swedpat said:
*What would you expect for total effective runtime at turbomode?
Based on the above, a little over an hour on my 2200mAh cells. Should be proportionately longer on larger capacity.
 
Last edited:

MichaelW

Flashlight Enthusiast
Joined
Dec 8, 2007
Messages
1,789
Location
USA
You'd figure Fenix would have the step down on Turbo, be to a somewhat higher output than just High, say 1200 lumens.
That level should allow flat regulation with 4x cr123A or 2x 18650, and probably shouldn't overheat in the real world (and if it did, step down to the 800 lumen mode)
 

selfbuilt

Flashaholic
Joined
May 27, 2006
Messages
6,936
Location
Canada
You'd figure Fenix would have the step down on Turbo, be to a somewhat higher output than just High, say 1200 lumens.
That level should allow flat regulation with 4x cr123A or 2x 18650, and probably shouldn't overheat in the real world (and if it did, step down to the 800 lumen mode)
I'd have to let those with more circuit experience comment, but my impression (based on the early MT-G2 lights I've tested) is that it seems to be hard to keep them flat-stabilized at higher current draws. Note sure how much it matters, but the forward voltage of these MT-G2 emitters is higher than standard flashlight LEDs. :shrug:

Of course, the step-down decision here may simply have been one of convenience - unlike many lights, the TK35UE "officially" changes mode to Hi as a step-down feature (i.e., which is why a single mode-click brings you back up to Turbo).
 

Swedpat

Flashlight Enthusiast
Joined
Jan 5, 2008
Messages
3,448
Location
Boden, Sweden
One comment there - my relative output scale (on the graphs) is not the same as lumens. My estimated lumen scale is based on the power relationship coversion of raw lightbox output. So you would need restate the runtime graphs in estimated lumens (at least approximately) in order to do a true lumen-hours comparison.

All that said, my TK35UE is indeed an unusually good performer for a MT-G2 light. :whistle:

Hard to say, but I would expect it's a reasonable one.

I have gone and done repeated re-starts every 5 mins on Turbo (below) - but these were all done under a cooling fan, and giving the light a few mins to cool before re-starting. I've edited out the pauses to better show what to expect (the spikes show the time I shut-down). I've also plotted it on my estimated lumen scale, for better resolution.

As you can see, the light seems to be largely direct-drive on Turbo, eventually dropping to the Hi level around the time that the batteries are nearly exhausted.


Based on the above, a little over an hour on my 2200mAh cells. Should be proportionately longer on larger capacity.


What I thought about was your measured values for TK35UE compared to TN35 at Hi mode vs level 4:

TK35UE: 2h 28m at 800lm - 2,47h x 800lm = 1976 lumen hours

TN35: 2h 43m at 1010lm - 2,72h x 1010lm = 2747 lumen hours

Then I calculate: 2747/1976 = 1,39 = 39% more lumen hours with TN35 despite the battery capacity is 50% higher. Yes; the 800lm does not fall completely straight down as with level 4 of TN35 so the difference will be slightly less.

I think the much more substantial head of TN35 should weigh up when it comes to heat dissipation for the slightly higher output in this case.
But: at turbomode with TK35UE it's really obvious according to your runtime graph that two cells can't handle the output as good as three cells with TN35.
As you show TK35UE isn't regulated at all at the 1800(2000)lm mode, while TN35 can provide almost flat output until end at ~2400lm.

Therefore in my opinion it would be more fair to name turbomode of TK35UE as a boost mode. It had been better if TK35UE had turbomode as 1400-1500lm. Maybe it could then be regulated and not limited to 5min step down. But as we know: lumen number sells better than flat output or useful runtime and therefore we see many lights of different brands with many lumens as a selling argument even if these lumens hardly are useful.
Malkoff Devices flashlights is a great example of the opposite.

Having that said: TK35UE is still an attractive light.
 
Last edited:

selfbuilt

Flashaholic
Joined
May 27, 2006
Messages
6,936
Location
Canada
What I thought about was your measured values for TK35UE compared to TN35 at Hi mode vs level 4:
... Therefore in my opinion it would be more fair to name turbomode of TK35UE as a boost mode. .
Yes, I'd say those numbers are an accurate distillation from my runtime graphs.

To be fair though, flat-regulation is really more of a selling feature for those who look at runtime graphs. ;) In practical terms, you wouldn't notice that sort of Turbo output drop off in use (i.e., it is only a ~5% reduction over 5 mins - far too slow to detect visually).

I suppose another way to look at it as that each time you re-start the light after a 5 min Turbo mode run, you are down another ~5% from max Turbo. So after ~1 hour of restarts, you are down to the Hi level (at least on my 2200mAh cells - you'd do better with higher capacity cells).
 

ma tumba

Flashlight Enthusiast
Joined
Oct 7, 2013
Messages
1,341
Location
Russia
is it possible to take the smooth reflector from the original tk35, and put it to the new tk35 in order to check if it makes it a bit more of a thrower?
 

selfbuilt

Flashaholic
Joined
May 27, 2006
Messages
6,936
Location
Canada
is it possible to take the smooth reflector from the original tk35, and put it to the new tk35 in order to check if it makes it a bit more of a thrower?
Well, you would have to modify the original TK35 reflector to increase the opening for the larger MT-G2 emitter. And judging from the sealed head design, you would have to remove the circuit housing/pills etc to access the reflectors from behind. Not sure it is worth the effort, as any change from texturing to smooth would be minimal on the beam (i.e., all texturing really does is fuzz-out the edges of the hotspot, and increase the corona). I doubt you would see much of a difference at all. The MT-G2 is never going to be any kind of thrower in this build.
 

Swedpat

Flashlight Enthusiast
Joined
Jan 5, 2008
Messages
3,448
Location
Boden, Sweden
Yes, I'd say those numbers are an accurate distillation from my runtime graphs.

To be fair though, flat-regulation is really more of a selling feature for those who look at runtime graphs. ;) In practical terms, you wouldn't notice that sort of Turbo output drop off in use (i.e., it is only a ~5% reduction over 5 mins - far too slow to detect visually).

I suppose another way to look at it as that each time you re-start the light after a 5 min Turbo mode run, you are down another ~5% from max Turbo. So after ~1 hour of restarts, you are down to the Hi level (at least on my 2200mAh cells - you'd do better with higher capacity cells).

Yes, it's not that bad when I think about it. If I think correct: after 1 hour at hi mode(without any minute at turbo) I should get at least 1400lm at turbomode so that is pretty good.
 

scintillator

Enlightened
Joined
Jan 21, 2008
Messages
309
Great review selfbuilt you are really a great asset here on the forums.
I have the original tk35 and have not really been pleased with the tint,but still like the light.
This looks promising.
 

selfbuilt

Flashaholic
Joined
May 27, 2006
Messages
6,936
Location
Canada
I have the original tk35 and have not really been pleased with the tint,but still like the light.
This looks promising.
Yes, that was one of my issues with the original TK35 as well (i.e., my XM-L sample had one of the greenest tints I have ever seen in a commercial light).

The nice thing MT-G2 emitters is that they are all a pleasing (to my eye) neutral white. Although this some range in the samples I've seen, most would fall into the ~5000K to ~4500K range. It is just the relative lack of throw on the TK35 build that may give some people pause to consider.
 

leon2245

Flashlight Enthusiast
Joined
Apr 4, 2008
Messages
2,335
We don't know the spot intensity on high correct, because that 17,800cd is measured during its 5 minute mode?
 

selfbuilt

Flashaholic
Joined
May 27, 2006
Messages
6,936
Location
Canada
We don't know the spot intensity on high correct, because that 17,800cd is measured during its 5 minute mode?
That's right, I don't typically do beam intensity measures outside of the ANSI FL-1 standard time window for Peak intensity. I can try to to do this on Hi next time I'm testing some lights, and report back.
 
Top