# Fenix LD41 prototype Review



## subwoofer (Apr 8, 2012)

Fenix are updating the LD40 with an XM-L emitter. On test here is a prototype (not even pre-production) of the LD41.

All comments in this review are limited to the prototype sample I have. The final LD41 may differ slightly from this early prototype.


Initial Impressions:

The LD41 prototype is all metal, and has a similar rectangular battery tube to the LD40 to hold the 4xAA that power this light. In this sample the edges of the rectangular profile would benefit from some rounding off to give a more comfortable shape to grip.

The LD41 is a very good size and weight, and odd though it may seem, the light fits well in your hand and makes it extremely resistant to rolling.



What is in the box:

Being a prototype, there was no packaging or spares provided, so this section is not applicable here.

LD41 - as supplied









Looking inside:

Now looking from the top to show the rectangular cross section of the LD41 (compare to the side view shown above)






Looking directly at the tail switch shows the larger forward clicky switch and smaller mode changing switch. The plate holding the switch rubber covers is fixed with four screws and the plate itself in this prototype is steel. There is evidence of minor corrosion from finger prints showing on this plate.






Looking directly at the LED






The contacts in the head are typical Fenix style, but as this is a prototype, the finish is not that neat.






The threads are trapezoid and a single o-ring is used






With the battery holder still in the battery tube, you can see the circular negative contact surrounding the central positive contact. Again as a prototype, the parts used are not of a final production quality






The battery holder has a 4S circuit with 2x2 layout (measure voltage is around 4.7V with Ni-mh depending on charge level). This holder looks like it is the same as the LD40’s.






And switches which are integral to the battery holder (the battery tube only holds the switch rubbers, not the switches themselves)








Modes and User Interface:

The tail-switch is a forward clicky giving instant access to the previously set constant output mode. Next to the power switch is the mode changing switch. The previously set constant output mode is remembered so the light will come on (or can be flashed using the momentary feature of the forward clicky switch) in this memorised mode.

To change modes the mode selection switch is used in two different ways:

To cycle through the four constant modes, a brief press of the mode change switch changes from low->med->high->turbo

If you press and hold the mode switch while the light is on, after ~2s the light enters the two speed strobe, and if you keep holding it for a further 2s an SOS mode is activated.

Switching the light off and on, or a brief press of the mode switch changes back to the constant mode.





Batteries and output:

Supporting only standard AA battery types the LD41 is likely going to be optimised for ni-mh as most Fenix lights are. As there are no specifications or instructions it is not clear if Lithium AAs (1.7V) will be supported, but it is likely they will be. Testing has been carried out with Eneloops.

As this prototype is not the finalised I do not have the output specifications, however I have just built an integrating sphere and have used this to get an approximate measurement of the constant output modes.






Based on my integrating sphere measurements and comparisons to other well known light sources to calibrate the sphere, I have found the following results:

Low – 5lm
Med – 76lm
High – 190lm
Turbo – 510lm

An early promotional material for the LD41 says it will have 458 max output, so this prototype may be performing above the final production models.











The modes are regulated and do not use PWM. When the batteries can no longer provide maximum output, the high mode simply dims gradually. As there is no sudden cut off so you will not be left in the dark and have plenty of warning.



In The Lab

_In an attempt to quantify the actual beam profile I developed the following test. There are probably many flaws in my method, but it is simple and easy to carry out and seems to provide a good enough comparison.

The method used was to put the light on the edge of a table 1m from a wall, with a tape measure on the wall. The zero of the scale is placed in the centre of the hotspot and a lux meter is then positioned at points along the scale, with the measurements recorded. Beam shots are often taken with the light shining on a flat white wall, so this method is simply measuring the actual intensity across the beam on a flat surface, not the spherical light emission.

The results are then plotted on a graph.

For the best throw you want to see a sharp peak with less of the distracting spill. For the best flood light the trace should be pretty flat._

The LD41 is shown here with the RC10 pre-production model I have on test (very similar beam to the TK15) and a ‘standard’ Cree R2 P60 module. The LD41 has a quite diffuse hotspot and nice floody beam.






_Taking this a little further, I calculated an approximate factor to apply to the lux measurements, as each measurement gets further from the centre of the beam, it corresponds to a larger area onto which the light is falling. It seems to me that this should also be taken into consideration, so I applied these area corrections and came up with this odd looking graph.

The key quantity here is the area under the graph line. This should correspond to the total light output._

The LD41 has a lot of light in its spill and a very impressive output.








The beam of the LD41 protoype

As a general purpose light, the LD41 has a well rounded beam. Great for shorter distances with a bright floody spill and still enough power for mid range use.

With the exposure set for a similar look to the naked eye (indoors on maximum is bright!)






And a reduced exposure to highlight the shape of the beam






Taking the LD41 outside I ran it next to the TK41 on a driving range

First the awesome TK41






Then the LD41






Moving to a nearby track, again first the TK41






Then the LD41








Using the LD41

The LD41 has proven itself to be an excellent midrange light. A bit too large to EDC, but not as large and heavy as the TK41 and TK45.

There is plently of power on offer here and a really useful beam for everything but searching long distances.

A rectangular cross section is not that common (though there are some other examples on the market) but it actually give a very positive grip and feels good in the hand. I have asked people with both large and small hands to try it, and they all liked it saying they felt they could hold it firmly and even the person with the smallest hands was happy using a cigar grip to turn it on and change modes.

Hopefully the final version will have the same maximum output as this prototype (which measure over 500lm) and the same beam profile.

With its unusual shape, the LD41 has proven a surprisingly good performer in every regard and gives a real AA powered alternative to the common P60 host 18650 form factor lights.




Test sample provided for review by The Photon Shop.

I’ll update post 2 of this thread once I have some more comments to add....


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## subwoofer (Apr 8, 2012)

reserved for further comments...


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## glugo1969 (Apr 8, 2012)

great review, all i can say is wow!


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## igoman (Apr 8, 2012)

Very nice review. Can you post a beam comparison with the TK21 or perhaps with the Jeatbeam PA40? The tint sure looks very similar to the TK21 and not as warm as on the LD40.

When did you take this picture, is that the moon? Looks like the sun .


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## subwoofer (Apr 8, 2012)

igoman said:


> Very nice review. Can you post a beam comparison with the TK21 or perhaps with the Jeatbeam PA40? The tint sure looks very similar to the TK21 and not as warm as on the LD40.
> 
> When did you take this picture, is that the moon? Looks like the sun .



If I remember I'll try to get a shot of the TK21-U2 with the LD41 next time I'm out doing beam shots.

Taking the raw integrating sphere measurements, the TK21-U2 gave 30.2, and the LD41 prototype gave 30.8, so the LD41 has a marginally higher output.

My TK21-U2 review:

http://www.candlepowerforums.com/vb/showthread.php?317515-Fenix-TK21-U2-–-A-review-in-four-parts

Does have a similar driving range shot of the TK21 vs the TK41, so this may give you an idea.

The LD40 uses a neutral emitter so appears warmer than the TK21 or LD41. The TK21 I have has a slightly green tint, but the LD41 is cool white.

It was a full moon when I took the photos, I included it in shot for atmosphere.


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## kj2 (Apr 8, 2012)

Very nice  thank you so much for the review


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## Harry999 (Apr 8, 2012)

This looks very nice. The LD40 is a good thrower and the LD41 looks to take advantage of the floody characteristics of the XM-L led. Personally this is one I am interested in. An neutral led would suit me better and I wonder in the production model like the LD40 will have a neutral tint. If not I may be asking for someone to mod it for me.


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## Enzo (Apr 9, 2012)

The look and interface appears similar to my TK35. Just wish Fenix would switch to a metal battery carrier which is my complaint on the TK35. 
Great review, thanks!


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## Chicago X (Apr 9, 2012)

Very nice review, thanks for sharing.

The looks of this light are very appealing - almost an amalgam of the TK35 and LD40.

Do you know if the heads are interchangeable with the LD40 or PA40 ?

How is the tint? Any hint of green?


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## Racer (Apr 9, 2012)

I'm not sure I understand Fenix's motivation for this. Prototypes by definition are something which are subject to change before they hit the shelves. That's why you rarely if ever see prototypes being reviewed for any product, not just flashlights. Because the thing being reviewed is almost always different by release time. Seems like Fenix is just fishing to see if there's enough interest in even bringing this product to market in the first place. I'm not sure I see the point of reviewing something that doesn't technically exist.


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## HKJ (Apr 9, 2012)

Racer said:


> That's why you rarely if ever see prototypes being reviewed for any product, not just flashlights.



That is not correct, I have had 4 prototype/pre-production lights for review in the last couple of months.


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## Racer (Apr 9, 2012)

In my mind, there's a big difference between a prototype and a pre-production unit. I would normally consider a prototype to be something experimental, where pre-production is something that's on its way to being mass produced. Not all prototypes see production. Where pre-production (by definition) is something that's definitely going into production.

I do understand that flashlights are a different animal than the tech industry I'm normally used to dealing with. For example, I think of Apple, whose prototypes are usually a closely guarded secret.


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## marc123 (Apr 10, 2012)

The tint on it looks to me more towards the neutral spectrum than cool white in those beamshots. Looks warmer than the TK41 anyway. I think I will be in for this one, it would be neat to know what the runtimes are. That might be the decider for me.


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## whiteoakjoe (Apr 11, 2012)

I have been waiting for this one, I have the LD40 and Jetbeam PA40neutral, and the PA40 has become my favorite light. Looks like that might change...


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## jamesmyname (Apr 12, 2012)

I contemplated for a long time between the LD40 and PA40 for my first "real" light. I went with the PA40W for the XML and neutral tint, but I think I would have been happy with either light. I think I'll appreciate the PA40's battery indicator, but the LD40's mode switch would be very nice to have. It would be amazing if the battery indicator could be depressed like a switch and change modes. 

Anyway, I look forward to seeing the LD41. I don't think I'll regret getting the PA40; I love that light. And hey, isn't the motto here, "just get them both!"


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## braddy (Apr 16, 2012)

marc123 said:


> The tint on it looks to me more towards the neutral spectrum than cool white in those beamshots. Looks warmer than the TK41 anyway. I think I will be in for this one, it would be neat to know what the runtimes are. That might be the decider for me.



I was told today by the Fenix Store that the LD41 would burn 3 hours at 458 Lumens, and 300 hours at the 4 Lumens, I didn't ask about the other ranges.


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## braddy (Apr 16, 2012)

Thanks for the review, having only learned about the LD41 this morning, I sure didn't expect to see a review about it this afternoon.

Is there protection to keep our NiMH batteries from over-discharging?


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## marc123 (Apr 17, 2012)

braddy said:


> Thanks for the review, having only learned about the LD41 this morning, I sure didn't expect to see a review about it this afternoon.
> 
> Is there protection to keep our NiMH batteries from over-discharging?



Thanks for the info on runtimes. Did they give an updated release date?


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## subwoofer (Apr 17, 2012)

braddy said:


> Thanks for the review, having only learned about the LD41 this morning, I sure didn't expect to see a review about it this afternoon.
> 
> Is there protection to keep our NiMH batteries from over-discharging?



I can't think of any Ni-Mh powered device that has over discharge protection, as Ni-Mhs are difficult to damage even if you wanted to. In my experience it is only li-ion powered devices that may have built in protection. Also in order to make the most of the very last bit of power from, say a set of alkalines, the LD41 will draw whatever power it can to maintain some output. Bear in mind that the LD41 is a 4S battery configuration so it is likely that when running very low, it will reverse charge the lowest cell however well you try to match the cells. This is in no way a weakness or problem with the LD41, but is perfectly normal for a multi-cell light.


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## mocha_jo1 (Apr 22, 2012)

Great beamshot. I like the separate mode changing switch as well.


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## eebowler (Jun 27, 2012)

subwoofer. Thank you for the great review. I in particular like your beam profile graph!


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## kj2 (Jul 13, 2012)

Had this light in my hand yesterday. Feels good, looks good  Only the specs aren't that great. 520lumens is good, but 10000cd and 200meters throw- that isn't very much. Do think this light won't be a best-seller. Think that the E40 will do much better.


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## subwoofer (Jul 13, 2012)

kj2 said:


> Had this light in my hand yesterday. Feels good, looks good  Only the specs aren't that great. 520lumens is good, but 10000cd and 200meters throw- that isn't very much. Do think this light won't be a best-seller. Think that the E40 will do much better.



The nice wide hotspot makes the beam a great all purpose light and the lack of peak beam intensity and throw is exactly why I would buy this. If you want throw, buy a thrower, if you want a bright AA powered light for general use then the LD41 fits the bill very well.


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## kj2 (Jul 13, 2012)

subwoofer said:


> The nice wide hotspot makes the beam a great all purpose light and the lack of peak beam intensity and throw is exactly why I would buy this. If you want throw, buy a thrower, if you want a bright AA powered light for general use then the LD41 fits the bill very well.



IMO the Fenix E40 will fit people more. Cheaper, yes also less lumens- but higher intensity and more throw. But specially the lower price makes it nice.


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## subwoofer (Jul 13, 2012)

kj2 said:


> IMO the Fenix E40 will fit people more. Cheaper, yes also less lumens- but higher intensity and more throw. But specially the lower price makes it nice.



Cheaper, yes many will choose it because of that, but throw?

What do most people want a light for? Walking about the house, looking under the stairs of in a cellar. In the garage, walking the dog etc, hardly any of these would need a beam range over 50m.

When you have a high peak intensity, you will find that at closer ranges you get what I call hotspot blindness, the effect of a tiny very bright hotspot making it so you can't actually see anything outside of the hotspot, unless you ceiling bounce the beam. It is much more natural to have a wide hotspot and loads of spill (and less throw). Throwers are fun and can impress friends but are of limited practical use.

A great number of cheap lights with relatively low output make up for it by focusing the beam into a tight hotspot. It looks impressive until you actually try to use it. I have several lights which I cannot use around the house or even out walking as the hotspot is too bright and small, yes they are great for throw, but not much else.

So in summary, I might agree that the cheaper price point will be attractive, but at the cost of a better beam for general use, and the higher overall output of the LD41.


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## kj2 (Jul 13, 2012)

subwoofer said:


> Cheaper, yes many will choose it because of that, but throw?
> 
> What do most people want a light for? Walking about the house, looking under the stairs of in a cellar. In the garage, walking the dog etc, hardly any of these would need a beam range over 50m.
> 
> ...


Would like to see the difference between both. Hope that video's will hit YouTube soon. 
And 10000cd is for indoors still a lot. I have the TK21, does 11489cd on turbo, and that's way to much for indoors.


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## igoman (Jul 16, 2012)

The LD40 throws 207m and the LD41 200m. Is the diference really so negigible?


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## PhantomAntichrist (Aug 11, 2012)

Just ordered mine at at Light Junction for $64.95 including shipping. My first high power flashlight. How will Duracell 2000 Mah batteries work in this light?


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## martinaee (Nov 4, 2012)

Honestly looking at the second shot comparison between the LD41 and the TK41 on turbo I am very impressed with the LD41. It looks as though it actually is brighter at midrange lighting up a larger hotspot though not throwing quite as far. I think this shows that the perceived brightness difference between 520lm and the 800(first version xm-l I presume) tk41 is not that big. If the LD41 had a slightly deeper parabolic reflector it would look more or less like the tk41 with maybe a third stop difference brightness in photographs?

I'm have to hold myself back right now in terms of flashlight spending so I'm torn whether I want to splurge on something like a LD41 or something like the upcoming TK22... Also the TK15-S2 is still VERY attractive to me as a tougher light than the LD41, but with sorta similar brightness. Hmmm.... If only one of these three used a T6 neutral xm-l that would make my decision a lot easier. I'm kinda pizzed that only the upcoming E50 is getting a neutral xm-l.


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## Jash (Feb 5, 2014)

I really wanted an LD41 when they first came out, but the output wasn't enough to justify it over the LD40 I already had, plus 10k lux wasn't exactly impressive.

The updated LD41 with 680 lumens and 18k lux is much more attractive, and I should have one in my hands by lunchtime today. 

Seems the TK40 will finally be replaced


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## Labrador72 (Feb 5, 2014)

Remember what you said a while ago... :devil:


Jash said:


> I ain't ever getting rid of my TK40!


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## Jash (Feb 8, 2014)

Labrador72 said:


> Remember what you said a while ago... :devil:



Hey, hey, hey... I said I'd never sell it. Didn't say it wouldn't be replaced. The LD41 has become the new bedside light to accompany the Quark NW Regular. That *was* the domain of the TK40.

I've given the TK40 to my son. His old 4D Maglite with Terralux dropin just doesn't cut it anymore. His eyes nearly popped out of his head when I told him he could have it to use.

Should be interesting going on camping trips now when his friends pull out their 20 lumen cheapies, and my son pulls out the awesome TK40. They like to play spot light a lot. Me thinks the game won't be so fair now.


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