Fenix LD75C Review (4xXM-L2 U2 & 1xXM-L color, 4x18650 or 8xCR123A)

candle lamp

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This is a review for the Fenix LD75C prototype sample.
The LD75C is a latest member of the LD series from Fenix. It is high-output light using 4xXM-L2 U2 and 1xXM-L color LEDs, with double circuits and new three electronic switches in the head. It runs on 4x18650 or 8xCR123A, and features thermal regulation to avoid overheating the light.

Fenix sent to me only a prototype light. The shipping version will include wrist lanyard, extra o-ring, hoster, user manual, warranty card with cardboard box.
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Manufacturer Specifications from Fenix website :

• Utilizes Cree XM-L2 U2 LEDs and XM-L color LED with a lifespan of 50,000 hours
• Powered by 4 rechargeable Li-ion 18650 batteries or 8 CR123A lithium batteries
• 158mm (6.22’’) x 52mm (2.04’’) x 74mm (2.91’’)
• 430-gram (15.16oz) excluding batteries
• Digitally regulated output - maintains constant brightness
• Double circuit design for flexible power options and better reliability
• Reverse polarity protection guards against improper battery installation
• Over-heat protection to avoid high-temperature of the surface
• Side switches for ON/OFF and output selection
• Made of durable aircraft-grade aluminum
• Premium Type III hard-anodized anti-abrasive finish
• Toughened ultra-clear glass lens with anti-reflective coating

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Anodizing is a matte black, presume to be hard anodized (type III), but there are a couple of chips on my sample (i.e., prototype sample, so it may have already seen some handling (i.e., already used). Labels are minimal.
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The light has mainly 2 parts (i.e. head+battery tube, and tailcap). There is no battery carrier on the LD75C.
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The light comes with a stainless steel scalloped bezel ring. There are thick cooling fins on the head.
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The light seems to use AR coating lens, and the purple hue is reflected on it.
The LD75C uses four cool white XM-L2 U2 (main) LEDs and a XM-L (RGBW) color LED. The head is distinctive with four XM-L2 U2 emitters in relatively deep smooth reflector wells and one XM-L color emitter in a narrow, shallow heavily textured reflector well. Some emitters are not perfectly centered in their own reflector well. But it does not seem to affect the overall beam quality in the real world. Coupled with the overlapping reflector wells with a bit deep depth (,but not as big head as expected), so I would expect peripheral artifacts in the spillbeam and the reasonable throw of beam.
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The LD75C uses side electronic switches on the head to control on-off and mode switching. These switches are very distinctive, and you can make a number of modes by combining main LEDs and colored LED at the same time. Scroll down for user interface.
These switches are conveniently located on the head. The right upper switch controls on-off and output selection of 4xXM-L2 U2 LEDs (main LEDs). The left upper switch with a "C" logo on it controls on-off and mode selection of a XM-L color LED (colored LED). The bottom switch is for instant strobe and Turbo output directly.
The switch feel is good for an electronic switch. There is a reasonable traverse, and the action is firm. All switches provide audible click when engaged. Grip is good with the texturized rubber button cover.
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The light doesn't use a battery carrier, but instead four cut-out wells for the cells. The cells are arranged in 2S2P for 4x18650. Connection is made by raised contact points on the disc in the tailcap. The tailcap disc can spin freely, and locks in place to a set of spring-mounted pins in the body that line up with holes in the tailcap. The positive & negative contact points in the tailcap are all spring-loaded structure, and there are all spring contacts in the head.

True flat-tops, wide and small button-tops of 18650's should work fine, as all contact points in the head and the tailcap are raised. All my longer and wide protected high capacity cells fit fine. You should be careful to insert the 18650's into the battery wells in the correct polarity. But you need feel no concern about the improper battery installation. The light has reverse polarity protection to protect from improper battery installation (i.e., the electronics of the LD75C has in-built reverse polarity protection).
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You can see the fully loaded battery wells with unprotected 18650 cells. I don't have any issue with inserting my short & long 18650's then completely closing the tailcap. It introduces no rattle even when shaking the light laterally in case it's fully loaded with unprotected 18650's in my sample. Note that you can use 2x18650 or 4xCR123A the same way as above, thanks to 2S2P arrangement. The 18650 (or CR123A) batteries go in alternating orientation, as indicated by the "+", "-" labels on the body end and springs in the head.

One of the most obviously distinctive features of the LD75C is a double circuit design. Each circuit controls 2xXM-L2 U2 LEDs and 1xXM-L color LED. So when using 2x18650 (or 4xCR123A), main LEDs have each half-reduced output with same runtime - note that only two main XM-L2 U2 LEDs will work in case of using a half of cells. But colored LED maintains full output with half the runtime in the same case.
So you can turn on the light and use it, provided all two circuits do not break down. This is a very good circuit design. To check it, scroll down for runtime part.
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Screw threads are square cut, and seem good quality. Both male & female threads on the body and tailcap are fully anodized, but lock-out is somewhat complicated. A quick turn of the tailcap doesn't prevent activation through the head switches, but the standby current persists until the tailcap is loosened about 4 full turns (i.e., you will need to unscrew the tailcap 4 turns from tight to completely block the standby drain) when not in use. Note that it takes about 5 full turns to fully tighten - remove the tailcap. I found screw threads to be a bit rough, due to lack of lube on the screw threads on my sample. It seems this is due to the used prototype sample.
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The body tube continues the cylindrical shape. The overall embossed pattern of the handle has many shallow ribs which have eight-number of horizontal ridges running the length of the body tube. This pattern gives adequate grip, as there are sufficient grip elements to help with grip. Tube wall is thick and sturdy.
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There are a couple of holes at the rear end of the tailcap for lanyard attachment.
I found the light can tailstand with the lanyard attached stably.
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From left to right, VicLite 18650 protected, Lumintop PS03 (3xXM-L2 U2), Imalent DDT40
(4xXM-L2 U3 & 2xXP-L), Fenix LD75C (4xXM-L2 U2 & 1xXM-L Color), Supbeam X40 (3xXM-L2 U2), Fenix TK75 (3xXM-L U2)
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The head size & body weight excluding battery of each light are as follows :
PS03 : 54.8mm / 313g, DDT40 : 54.5x54.6mm / 369g, LD75C : 73.9mm / 431g, TK75 : 87.9mm / 506g
Despite the addition of the extra emitters, the LD75C has a smaller head than the TK75.
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The gripability is good. The build feels solid, and handling & balance of the light is good. The overall build quality is excellent.
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Measured Dimensions & Weight

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User Interface

Main LEDs (4xXM-L2 U2) :
Press and hold the upper right switch with "power" logo for 0.5 seconds to turn on the main LEDs. While on, click the same switch repeatedly to cycle between the five main output levels in the following repeating sequence : Eco -> Low -> Mid. -> High - > Turbo. Turn the light off by pressing and holding the same switch for 0.5 seconds again. The light has mode memory, and will return to the last level used when turned back on from off.

Colored LED (1xXM-L RGBW):
Press and hold the upper left switch with "C" logo for 0.5 seconds to turn on the colored LED. While on, click the same switch repeatedly to cycle between the six modes in the following repeating sequence : Blue -> Green -> Red -> White -> Red slow flashing -> Red/Blue Strobe. Turn the light off by pressing and holding the same switch for 0.5 seconds again. The light will activate in the last memorized colored mode from off. The Red/Blue strobe is similar to that use by police services, in my view.

Note that you can get max. output (4,200lms) by combining "Turbo (4,000lms)" of the main LEDs and "white color (200lms)" of the colored LED. Like this, you can make a lot of different combinations of the main modes and the colored modes.

Full power main LEDs strobe is activated by clicking the bottom switch. This works from both On and Off. Turn the light off by clicking the same switch.
You can jump to Turbo directly by pressing and holding the same switch for 1 seconds from Off. Turn the light off by clicking the same switch.

You can make some combinations of the Strobe mode and the colored modes.
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Standby Current Drain

Due to the electronic side switches, the light has a small current when batteries are making contact. I measured this current as 48.0μA with 2xVicLite 18650 (2600mAh) cells. Since the cells are arranged in 2S2P and the light has double circuits, that would translate into around 6 years before the cells would be fully drained. This is quite small and reasonable for a standby current, not a concern. If you want to break this current, store the light locked-out by unscrewing the tailcap 4 turns from tight or remove the batteries from the light when not in use for a very long time (i.e., a quick turn of the tailcap from tight will not completely block the side switch standby drain).
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PWM

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The light shows no sign of PWM at any output modes. I do think the light is actually current-controlled. I notice there is no buzzing sound on my sample.
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Runtime

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The above is the runtime with continuous cooling applied. Four runtime tests were carried out with 4x18650 and 2x18650 cells for Turbo and High.
The LD75C has the over-heat protection function in the light. You could see a gradual step-down and step-up even under cooling around 10 mins running on Turbo from an unbroken red line. I suspect this is because my cooling fan's rpms or a high temp. set point of the thermal sensor of the light seem to be lower than expected (i.e., it's a prototype sample). Then the light features additional automatic step-downs (High -> Mid. -> Low -> Eco) in output as battery capacity depletes. I think this automatic step-down feature is a very good idea. Most fully regulated lights shut off abruptly without warning, once the battery protection circuit is tripped, and this can leave you in the dark. So this kind of fully-regulated step-down pattern is good, in my view.
In case of 2x18650 cells on Turbo, you have a half-reduced output on every step-downs, but longer runtime than expected. This seems to be due to the battery's characteristics such as age, number of uses, and environmental condition.

Runtime performance is very good, and flat regulation is evident on High. Again, you could see the light dropped down to a Mid. output, instead of completely shutting off, as battery capacity depletes from an unbroken dark blue line. When using 2x18650 cells on High, you have a half-reduced output on each step-down, and almost the same runtime as 4x18650.
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For Turbo (i.e., max.), output, overall efficiency and regulation pattern are very good. The LD75C is a top performer.
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The above is a run without cooling to measure the surface temp. of the head with a thermal probe. The thermal probe was placed in-between the first cooling fins just above the switch part. The room temp. was 24.8~25.9 degrees C, and window was ajar in the test room. The resting temp. for LD75C was 27.5 degrees C.
Note that left y-axis is the relative output. The dotted brown line represents surface temperatures of the light in degrees centigrade should be read off the right y-axis.
The light gradually step-down and stabilize at the High output level to abate, and gradually step back to Turbo. This oscillations are continued on the Turbo runtime.
Maximum external temperature of the light leveled off around 61.1 degrees C.
The light steps down from Turbo to High detecting the temperature (i.e., not a timed step-down, but automatically adjust the output of current brightness to avoid overheating). It also shows some distinct step-downs at the stage of battery depletion.
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This is a comparison with and without fan cooling to compare how the light activate. I mentioned before in my review, a lower cooling fan's rpms may not make the light stepped-down. The lack of cooling caused a more initial drop in output, but it's practically impossible for you to see the difference visually. The oscillations in output for thermal control resulted in longer runtime.
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Beamshot

1. White door beamshot (about 50cm from the white door) on max. output on 4x18650 (2600mAh) VicLite protected cells
- ISO100, F/8.0, 1/250sec, Auto white balance
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- ISO100, F/8.0, 1/500sec, Auto white balance
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- ISO100, F/8.0, 1/1250sec, Auto white balance
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Due to the smaller and shallower reflector design, the LD75C has a wider spillbeam than the TK75. Coupled with the overlapping reflector wells, there are spillbeam artifacts that are typical for this class. But, it absolutely depends on what distance and what output level you are using the light.
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- ISO100, F/2.8, 1/160sec, Auto white balance
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As you can see above, the Red, Green, and White LED mode are brighter than the Blue LED mode. The intensity of the colored LED seems much better than expect. There are some artifacts in the color beams, but it depends on what distance you are using the light. As mentioned in my review, you can make a lot of different combinations of the main LED modes and the colored LED modes.
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2. Indoor beamshot (about 7m from the target) on max. output on 4x18650 (2600mAh) VicLite protected cells
- ISO100, F/2.8, 1/15sec, Auto white balance
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- ISO100, F/2.8, 1/2sec, Auto white balance
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The Red, Green, and White LED modes provide a fair amount of light.
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3. 55m Outdoor Beamshot on max. output on 4x18650 (2600mAh) VicLite protected cells
- ISO100, F/2.8, 1sec, Auto white balance
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4. 60~65m Outdoor Beamshot on max. output on 4x18650 (2600mAh) VicLite protected cells
- ISO100, F/2.8, 1sec, Auto white balance
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The LD75C has a bright spillbeam, not much as much dedicated throw as the TK75. But it is a fairly high-output light with not only good throw, but reasonably flood beam.


The LD75C was provided by Fenix for review.
 
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Kalpn

Newly Enlightened
Joined
Aug 14, 2014
Messages
54
Thanks for the review! Can't wait for my LD75C to arrive.
 

MJ23

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Apr 2, 2015
Messages
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Thanks for the review! I would like a moonlight mode, but all in all i like it!
 

NoNotAgain

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Jan 25, 2014
Messages
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Location
Blue Ridge Mountains, VA
Thank you for the review.

Below the run time chart is a statement that the light was tested with the thermal control function turned off. Do you know how to turn it off?

The lumen ratings for the colored led's in the same chart don't by my eye align with what my limited use of the production light shows.

Also the blue led is close to the ultra violet spectrum as a comforter that I have on my sofa has a patch work that shows a florescence like I see when using a Nitecore P20UV or a Led Lenser V2UV light.
 

candle lamp

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Messages
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Thanks for all your supports! :)

Below the run time chart is a statement that the light was tested with the thermal control function turned off. Do you know how to turn it off?

Sorry. There's no way to turn it off for the users like you and me. As far as I know, Fenix tested the light without thermal sensor in the light in their lab.

The lumen ratings for the colored led's in the same chart don't by my eye align with what my limited use of the production light shows..

The lumens for the colored LEDs are somewhat bright to use the light indoors (or at very close distance).

Also the blue led is close to the ultra violet spectrum as a comforter that I have on my sofa has a patch work that shows a florescence like I see when using a Nitecore P20UV or a Led Lenser V2UV light.

Actually I don't know the wavelangth range of the lights. Is it about 365nm?
Now I'm wondering what the specific wavelength ranges are for the XM-L colored LED.
Fenix doen't provide this in their website (,and I don't have a manual). But according to the Cree XM-L color LEDs document, dominant wavelength range of the Blue is 450~465nm.
 

newbie66

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Mar 2, 2013
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Malaysia
Come on newbie66. Slide on up to the plate and get yourself one of these beauties.

All the colors under the rainbow in one light. Hot spot isn't bad either.

Lol! I am quite tempted to get one I will admit, but good thing my local dealer has not brought it in yet for some reason. Sooo a good excuse to not get it....for now. :p
 

candle lamp

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Joined
Jun 16, 2010
Messages
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South Korea
All the colors under the rainbow in one light. Hot spot isn't bad either.

The throwy lights tend to have more artifacts than floodier lights in the spillbeam part, in my view. The LD75C is a throwy light than floodier one. Its overall beam is not bad comparing to other throwy lights with multi-LEDs installed. Personally I like the main beam. :thumbsup:
 
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