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Thread: Fenix LD40 Review

  1. #1

    Default Fenix LD40 Review

    for submission in the Reviews forum

    Fenix LD40

    Manufacturer Specifications

    Cree XP-G Neutral-White LED (R4) (50,000 hour lifespan)

    Battery: 4 x AA (NiMH, Alkaline)


    -Length: 180mm

    -Diameter: 40mm

    -Weight: 170 grams (excluding batteries)

    - Digitally-regulated circuit maintains constant brightness

    - Patented physical structure avoids circuit damage from reverse battery polarity

    - Tactical push-button tail cap switch for momentary-on

    - Dual switches for simple, fast operation

    - Emitter housing/head made from aircraft-grade aluminum

    - Flashlight body made from high-quality plastic

    - Toughened ultra-clear double glass lens with anti-reflective coating

    Output Modes

    -Turbo: 248 lumens, 3 hours 13 minutes

    -High: 110 lumens, 9 hours 42 minutes

    -Mid: 43 lumens, 27 hours

    -Low: 4 lumens, 245 hours

    -Strobe: 278 lumens

    -Slow flash: 64 lumens

    -SOS: 64 lumens

    -Impact resistance: 1.5m

    -Waterproof: IPX-8, 2 meters

    The Fenix LD40 arrived in normal Fenix packaging with the usual included accessories (holster, lanyard, spare o-ring)


    The design of the LD40 is for me a first, with 4xAA batteries in a 2xAA side-by-side format. This gives the flashlight a unique shape which fits into the hand very comfortably. With the more common 2xAA format, the handle portion of the flashlight tends to be a rather slim, perfectly round tube which does not offer the best grip. As far as I am concerned, the knurling on standard cylindrical flashlights is done as a way of adding extra grip but to me the shape of the actual part of the flashlight that is in my hand is what is ultimately most important for grip. Further on the topic, the majority of my tools don’t have perfectly cylindrical handles, whether it be hammers, axes, etc. I always find that I prefer a somewhat flat surface up against my palm when I am holding something. On this aspect, I believe Fenix has hit the mark perfectly.

    The handle on the LD40 is not metal but seems to be some sort of plastic polymer (perhaps acrylonitrile plastic) which seems durable and definitely not cheap. I can imagine that this will be a topic of debate for most people but there are positives and negatives for both sides.

    First the positives. The plastic allows Fenix to be more flexible with the design of the flashlight which in this particular case resulted in a rectangular body which is great for grip. If I am not mistaken, all of Fenix’s previous metal designs have been cylindrical. The plastic is also going to be better for colder temperatures where metal can get quite cold to bare skin. The plastic also saves some weight, albeit not a significant amount. An important consideration which must not be overlooked is the price factor. I’m assuming Fenix will be able to offer this flashlight at a more competitive price because an all metal casing will likely cost more to produce. Whether or not that leads to a decline in quality is yet to be seen and is a good transition into the negatives.

    The rounded end of the LD40 means that it cannot tail stand.

    Over the years I have learned that there is no replacement for metal parts. They are just stronger and will last longer. This is not to say that these newer plastics are not durable, but I will have my reservations until it passes the test of time. Also, I can foresee there being problems with the threads between the head (metal) and the body (plastic). It seems that over time, the plastic threads will be worn down by the metal threads from the friction and twisting and this may compromise the seal. Some people also prefer the entire body to be made of metal in order to aid in heat dissipation from the LED. I will for now accept the new plastic design as something innovative and will see if it performs as it should in the future.

    Stock photos show various screws in the tail-cap area which have been removed in this production model. It seems the plastic has now been molded from the same piece so the tail “plate” no longer needs to be screwed onto the body. In my opinion, the fewer openings, the better. It’s hard to get a picture of the tail-end of the flashlight from inside the battery tube but this picture should give you an idea of how the “switches” on the outside do not include the actual switches, which are on the battery carrier itself. These buttons merely press up against the battery carrier switches when the battery carrier is placed inside.


    When first taking the LD40 out of the package and holding it, I was fearful that the balance would be completely top-heavy towards the aluminum head. It was very heavy on the head compared to the body and when held in my hand it would want to point down and slide out. This uneven balance can be attributed to the plastic yet again, but I was happy to note that when the batteries were installed, the balance was much better. It is still heavier in the front but not enough to make the balance uncomfortable. The balance/center of weight is approximately 80mm from the tip of the head. (The entire light is approx. 180mm in length)

    Design(head and reflector):

    The LD40 head is very large in comparison to Fenix’s 2xAA flashlights, having a diameter of approximately 40mm. The side-by-side battery carrier design has afforded Fenix the ability to make a wider flashlight with a much larger head and deeper reflector. This of course means more throw and the inclusion of a smooth reflector seems to assert this fact that Fenix intended this flashlight to be primarily a thrower. This is not to say that there is no spill, but the throw is definitely its strong point. Fenix claims the beam reaches 207m under FL1 standards.


    The LD40 uses an R4 Cree XP-G neutral white LED, providing a rated 248 lumens on its maximum setting. The color tint of this LED is slightly cooler than the TK20 but definitely a much warmer color than the normal cool tint on the Fenix L2D or LD20. Overall the beam is near-perfect with a nice warm color and no artifacts whatsoever. For outdoor purposes, which is where I will be using the flashlight, I believe neutral white is the way to go. The color rendition is far superior and enables me to identify objects at a distance far quicker because I can identify colors faster. Cool white LEDs make colors pale and for me this makes objects harder to identify. The LD40 is most definitely an outdoorsman’s light. The far reaching beam and color rendition are perfect for this.

    There is a very, very slight dark spot in the center of the beam. This is barely perceptible to the eye but in full discloser it is there. I almost did not notice it until I looked at the beam on a white wall out of the corner of my eye, which is more sensitive. For my purposes and I believe for any practical non white-wall hunting purposes, this small darker area is so small that it is irrelevant. The beam is otherwise flawless. The hotspot is very well defined and there is also a very bright spill just around the hotspot, an area perhaps 3 times larger in diameter than the hotspot itself. After that, there is an even brightness all the way to the outer rim of the beam.

    This comparison of beam tints show a TK20 on the right side in both pictures. In the top picture, the beam on the left is an L2D Q5 while on the bottom the left side is the LD40. You can see that the TK20’s beam is much warmer than the L2D but only barely warmer than the LD40.

    User Interface

    The LD40 has 4 different constant modes as well as 3 blinking modes.

    4 constant modes:

    The 4 constant modes are low (4 lumens), medium (43 lumens), high (110 lumens), and turbo (248 lumens). These modes are accessed by a completely separate metal button on the tail-end of the flashlight (different from the power button). By pressing this button and releasing, the mode will increase to the next higher setting. The light also has memory meaning it will switch on at the mode it was turned off at. Also to note, the LD40 has momentary-on meaning that the power switch does not need to be fully “clicked” on for the light to power up. A slight amount of pressure will turn it on. This is an important consideration for tactical use. The 4 lumen low mode is something which in my opinion should be looked at once again by Fenix. From personal experience, if I want a low mode, I want a low mode that is between 0.5 and 1 lumen. 4 lumens is simply too bright. That is not to say that it is not necessary, I believe the 4 lumen mode is perfect for walking around the neighborhood at night, but for inside the tent with a sleeping companion inches away, a lower low mode would definitely be appreciated. Having said this, I do believe it’s important to note that Fenix is heading in the right direction by continually lowering the output of its low modes. The L2D Q5 has a low mode of 12 lumens while the TK45 has a low of 8. This steady decrease in low mode lumens is a welcome trend by the manufacturer and I hope that it will continue.

    3 blinking modes:

    While I understand the purpose of including a blinking mode, I have become increasingly frustrated by the inclusion of these modes by various manufacturers who keep the blinking modes in the same “menu” as the normal modes, forcing the user to cycle through the blinking modes to return to a lower constant mode. This was a minor issue in the L2D and LD20 but I’m happy to report that Fenix has moved away from this by including blinking modes in a completely separate menu which can be entirely skipped by the user if he does not want to access it. This smart move by Fenix should keep everyone happy. On the LD40 the blinking modes are accessed by holding the brightness level button down for approximately one second. This brings the light into the blinking menu, in which there are 3 modes: SOS (64 lumens), slow flash (64 lumens), and a various frequency strobe (278 lumens). This latest option is one which I have yet to see on a flashlight. The strobe is not constant but rather varies between 15Hz and 6Hz every 2 seconds. I must say that it is incredibly disorienting as your eyes are not given a chance to adjust to the constant switching of frequencies. When I accessed this mode for the first time I was unaware that it changed frequencies and actually thought there was something wrong with my vision. If the purpose of strobe is to disorient, I think Fenix hit the mark with this new various frequency strobe.


    A strong point with the LD40 which is common in Fenix flashlights is the use of normal AA batteries which are easily obtained in the field. As a backpacker, it is important to me that my gear uses the same battery type so that I do not have to carry different battery types with me. It’s also important to me that I can stop by a gas station or convenience store and purchase spares.

    The battery holder is made of plastic and has a very slight rattle when the flashlight is shaken. The battery holder only fits into the battery tube in one direction and on one end has the buttons used for on/off and mode switching.

    This is the first time I have seen the battery carrier itself with the switches for mode operation. The tail end of the flashlight simply has covers for these buttons. Since the TK40 allows you to use half the required batteries (4 instead of 8) in emergency situations, I was curious to see if the LD40 would work with 2 instead of 4 batteries but it will not.

    Size and Form Factor:

    The LD40 is a flashlight that I would consider the best of two worlds. Previously, I would use an L2D, LD20, or TK20 for portability and outdoor use and a TK45 for sheer power and brightness. The LD40 takes a bit of both and combines it into one flashlight. The 4xAA batteries obviously will give me twice the runtime as smaller 2xAA models and it will also allow me to output 250 lumens for extended periods of time. While the TK40, TK30, and TK45 are excellent lights, they are simply not practical to use for backpacking and camping because of their size and weight. The LD40 is pocketable and weighs less than it looks like it should, perhaps because of the plastic housing. There is one gripe which I have which regards the location of the switches. While it may be just a personal preference, with a flashlight like this, I hold it by my waist in the palm of my hand. It would be much easier for me to switch modes if the switches were on the side of the head like on the TK45. I believe that rear clickies work well with smaller tactical lights sized 2xAA or under because of how they are generally held, in a tactical over the shoulder grip. I feel that with a 4xAA flashlight where weight and size are more of a factor, a traditional button placement on the side of the body near the head would be more practical and easier to access with one hand. For example I thought this was great improvement with the TK45 over the TK40.


    Overall, I believe the LD40 fits a category of flashlight that is not well represented in today’s market. The 4xAA configuration gives you runtime and power in addition to being portable. The multiple modes ranging from 4 lumens to 248 lumens makes it very practical to use for both low and high light situations and the larger and deeper reflector gives it great throw in the outdoors. This flashlight seems to have been designed as a “jack-of-all-trades” light for the typical outdoorsman and I believe that this is an accurate assessment of it. While I wish that the switches were on the side and not at the rear, and while I have certain fears about the plastic body, I have for the most part been very impressed with this latest offering from Fenix. It gets a big thumbs-up from me.

  2. #2

    Default Re: Fenix LD40 Review

    Thanks for the great review. This might be my solution for >100 lumens that go all night. Do you know if the LD40 has a lock out mechanism to prevent accidental turn on in my bag? For instance on many Fenix lights, unscrewing the tailcap a quarter turn will disable the light.


  3. #3
    Flashaholic* eebowler's Avatar
    Join Date
    Dec 2003
    Trinidad and Tobago.

    Default Re: Fenix LD40 Review

    Nice review OGreviews. Thanks.
    When was the last time you washed your feet?

  4. #4

    Default Re: Fenix LD40 Review

    I'm with you on the placement of the rear switch. They should just move it to the side and make the thing tail stand.

    Now that they are into these side by side configurations, I wonder when we can see a side by side 2AA version?

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