Warning: pic heavy, as usual!
The dual-head DT-20 by Skilhunt has been out for a few months, and is now available in a black anodized aluminum body (reviewed here). Let's see how it compares to other single and multi-emitter lights.
Manufacturer's Specifications and Features:
- 2 x CREE Xlamp XM-L U2 LED
- Max output: 1100 lumens, Max runtime: 120 hours
- Output/Runtime (tested on 2x3.7V 2400mAh Li-ion batteries:
- Double High Mode: 1100lm/1.5hr, Double Med mode: 440lm/3.5hr, Double Low mode: 30lm/60hr, Double Beacon: 440lm/7hr, Double Strobe: 1100lm/3h
- Single High mode: 550lm/3hr, Single Med mode: 220lm/7hr, Single Lo mode: 15lm/120hr, Single Beacon: 220lm/14hr, Single Strobe: 550lm/6 hour
- Power: 4xCR123A, 2x18650, 4xRCR123A (16340)
- Operating range: 3~9V
- Peak Beam Intensity: 22280cd
- Peak Distance: 298m
- Reflector: Durable aluminum vacuum plated orange peel reflector
- Body: 6061# aluminum
- Waterproof: IPX-8
- Impact resistance: 1.5m
- Special double LEDs with dual-circuit design providing a reliable safeguard.
- Parallel circuit design offers single led use. Can be powered by single 18650 battery in extreme-circumstances.
- Double holes and wide multi level design offer excellent heat dispersion
- Double side switch offer user-friendly interface to turn on/off and adjust output.
- 304 stainless steel bezel rings effectively protect the light from drops and impacts.
- Toughened ultra-clear glass lens with anti-reflective coating and diamond coating.
- Ergonomic design, Comfortable hold, and solid aluminum construction.
- Wide input range provides more choices of batteries.
- Reverse polarity protection, to protect from improper battery installation.
- Over-discharge protection circuit, protects the batteries effectively.
- Dimensions: Head (max) 73x37mm; Length: 151.5mm
- Weight: 280g (excluding battery)
- Accessories: Holster, 550 paracord lanyard, two spare switch cap rubber boots, four rubber o-rings, operator's manual.
- MSRP: $259 (but can be found online for less)
The DT-20 actually comes in two types of packaging – a presentation-style plastic carrying case (as seen in my earlier Defier series reviews), and the basic cardboard box shown above. Either way, you get the DT-20 light, belt-pouch carrying case, paracord-style wrist lanyard, o-ring lube, extra o-rings and boot covers, and manual.
From left to right: 4GREER 18650 3100mAh, Skilhunt DT-20, Fenix TK35, Nitecore TM11, Eagletac M3C4, Sunwayman M40C.
From left to right: 4GREER 18650 3100mAh, Skilhunt DT-20, Fenix TK35, Nitecore TM11, Eagletac M3C4, Sunwayman M40C.
Skilhunt DT-20: Weight 280.0g, Length: 152mm Width (bezel): 72.8mm and 36.8mm
Fenix TK35: Weight 256.1g, Length 162mm, Width (bezel): 48.6mm, Max Width 52.0mm
Sunwayman M40C: Weight: 258.5g, Length 156mm, Width (bezel) 57.1mm,
Eagletac M3C4 XM-L: Weight: 348.0g, Length: 164mm, Width: 61mm (bezel)
Xtar S1: Weight: 876.0g (est. 1028g with 3x18650 protected), Length: 240mm, Width (bezel): 83.4mm
Nitecore TM11: Weight: 342.6g (476g with 8xCR123A), Length 135.3mm, Width (bezel): 59.5mm
The design of the DT-20 is innovative. As you can see in the earlier photos, the dual-head DT-20 is not much larger than a compact 2x18650 single-emitter light. It's also very narrow for a side-by-side 2x18650 light.
Each head is independent of the other (i.e., the reflector wells don't overlap, separate bezel rings, etc.), although the aluminum frame surrounds both. Anodizing is a black matte finish on my sample, with no chips or damage. Labels are clear and bright against the background. There is no real knurling to speak of on the light, but various build elements do help with grip. Still, it could be a bit slippery if wet.
Switches are electronic switches, with typical feel for this class. The on/off switch is indicated by an embossed power logo, and is on the same side as the Skilhunt handle label. The mode-changing switch has a series of raised concentric rings, and is located on the other face where the model number is located. See my UI discussion below for more information.
Battery wells are physically independent of each other, with separate tailcaps. Note that screw threads are not anodized, so no tailcap lockout is possible. Fortunately, standby current is extremely low for the light - scroll down for a discussion.
Note that neither true flat-top (e.g., higher capacity AW cells) nor large button-top cells (e.g. Redilast) will work in the light, due to a raised plastic ring around the positive contact point in the heads. Only small button-top cells will work. Also, button top and/or cell height may be an issue – I had to use a small magnet for my AW IMR-18650 cells to work. But all my longer high capacity button top cells worked fine (i.e., my Xtar 3100mAh and 4GREER 3100mAh, and all my button-top 2200 and 2400mAh cells).
Note also that the battery wells are not actually in parallel (i.e., each has its own contact point and circuit). The circuits respond differently depending on the battery configuration (see my comments later in this review). Moreover, each emitter is not solely linked to just one well/circuit individually – you can run either emitter alone off a single cell in either well. Again, see my discussion below and at the end of the review for more info.
Turn the light on by pressing and releasing the On/Off electronic switch (i.e. the one with the power logo). A faint switch click will be heard. The light will come on in full power Hi mode, with both emitters activated.
The change the number of emitters, click the On/Off switch again. The light will cycle between both emitters > left emitter only > right emitter only, in repeating fashion.
Press and hold the On/Off switch to turn the light off.
Change output modes by clicking the secondary switch on the other side of the head. Light cycles between Hi > Med > Lo > Slow Beacon, in repeating order. Double-click the mode-control switch to access Tactical Strobe.
The light does not have mode memory, and always comes back on in Hi when you turn the light on. Same goes if you switch between the number of emitters using the On/Off button while on (i.e. it jumps back to Hi).
That might be clearer if you watch my video overview, for a more detailed examination of the build and user interface:
As always, the video was recorded in 720p, but YouTube typically defaults to 360p. Once the video is running, you can click on the configuration settings icon and select the higher 480p to 720p options. You can also run full-screen.
PWM on Med:
The DT-20 uses PWM for its Lo and Med output modes, measured at 1 kHz. This is a respectable PWM frequency, but it will still be visible to those who are sensitive to it (especially on Lo). Note that this is improved over the earlier Defier series Skilhunt lights, which were much more noticeable at just under 200 Hz. The DT-20 Lo mode is also lower than it was on the earlier Defier lights.
Slow Beacon mode:
The DT-20s slow beacon mode is at a perfect speed for my tastes, ~1.8 Hz. This means it is on for just under one second, and off for just under one second.
The beacon traces may look a little odd above, but that's because the light is not running at full power in beacon mode (i.e., it uses PWM):
Slow Beacon mode close-up of the On-phase PWM:
The PWM frequency is the same as the constant output modes, 1 kHz. The duty cycle appears to be about 50% - the same as the Med constant output mode (meaning the beacon mode will look to be same brightness as the half-power Med mode, when on).
The "hidden" strobe is a fairly standard fast tactical 10 Hz.
Due to the electronic switch design, the DT-20 will be drawing a small current when batteries are installed. I measured this current on a single 18650 cell, or 2xRCR in one well, as 48uA. For a standard 2600mAh 18650, would translate into over 6 years before being fully drained.
I am unable to measure the effect of 2x18650 properly, as the dual circuits react to the two battery channels separately (see my circuit discussion later in the review). If I insert an 18650 cell into the second well and close its connection – while continuously measuring from an 18650 in the first well - my DMM typically starts dropping rapidly from 48uA all the way down to zero. I suspect the circuits get confused by the partial presence of the DMM (i.e., the resistance in the DMM/leads - on one channel only - may confuse the circuits into thinking two different power sources are installed). It would seem that in this case, the DT-20 quickly shuts down the channel with the DMM connected. As I will discuss at end of the review, the DT-20 circuits are clearly able to distinguish between 2x or 1x 18650 cells.
It any case, I expect the 2x18650 current draw to be similarly negligible - which is fortunate as the tailcap screw threads are not anodized for lock-out
The head of the DT-20 has two independent reflector wells, each with a textured OP finish. Each reflector seems about typical for an individual single-emitter light (i.e. about one and a quarter inch wide at the opening, with reasonable depth). Individual cool-white XM-L emitters both looked well centered on my sample.
And now, what you have all been waiting for. All lights are on their respective max battery sources, about ~0.75 meter from a white wall (with the camera ~1.25 meters back from the wall). Automatic white balance on the camera, to minimize tint differences.
To keep this interesting, I am showing the effect of both emitters and a single emitter on the DT-20, compared to a multi-emitter and single-emitter light.
The DT-20 does a surprisingly good job at focusing the reflectors into a single hotspot, even at this incredibly close distance. But you could comfortably use the light on a single emitter if you wished
UPDATE May 9, 2012: Outdoor beamshots have now been added to the review. These are done in the style of my earlier 100-yard round-up review. Please see that thread for a discussion of the topography (i.e. the road dips in the distance, to better show you the corona in the mid-ground).
I thought I would compare for you above the difference between a single emitter and both emitters activated on the DT-20. I have also thrown in the Fenix TK35 as a comparator, because it is roughly similar in overall size.
Note the TK35 has a larger and and deeper reflector, so throw will be greater. Also, keep in mind that this location - and the camera settings - were chosen to best illustrate the relative throw of lights. In real life, the overall output of the TK35 appears to be roughly intermediate between the single and dual-emitter Hi modes of the DT-20.
The above is a comparison to higher-output 3xXM-L lights. Again, in real life, the DT-20 lit up this whole scene quite well (i.e. the camera settings don't really capture the overall brightness well).
All my output numbers are relative for my home-made light box setup, a la Quickbeam's flashlightreviews.com method. You can directly compare all my relative output values from different reviews - i.e. an output value of "10" in one graph is the same as "10" in another. All runtimes are done under a cooling fan, except for any extended run Lo/Min modes (i.e. >12 hours) which are done without cooling.
I have devised a method for converting my lightbox relative output values (ROV) to estimated Lumens. See my How to convert Selfbuilt's Lightbox values to Lumens thread for more info.
Throw/Output Summary Chart:
My summary tables are reported in a manner consistent with the ANSI FL-1 standard for flashlight testing. Effective March 2012, I have updated the Max Output ANSI FL-1 lumen estimates to represent peak output measured at 30 secs (my earlier gray tables were based on a later time point for Max output). Please see http://www.flashlightreviews.ca/FL1.htm for a discussion, and a description of all the terms used in these tables.
The reported ANSI FL-1 output specs are quite believable at all levels. In addition to values in the table above, I would estimate the double-emitter Med mode as ~500 lumens on 2x18650 (spec is 440 lumens), and the single-emitter Hi mode as ~580 lumens (spec is 550).
Note that the Lo mode is lower than the earlier Defier lights, and Lo/Med/Hi is better spaced now.
Throw is quite reasonable for the DT-20, given the size and shape of the reflector wells (and again consistent with reported ANSI FL-1 specs).
Let's start with an overview of 1x and 2x 18650 (AW protected 2200mAh) on the various levels and number of emitters.
Something interesting happens when you compare performance on 1x and 2x 18650 cells. You'll remember from my build discussion what each battery well appears to have its own circuit – but it turns out these are not uniquely linked to just one emitter, and can respond rather dynamically to different battery configurations.
With both emitters illuminated, output drops slightly if you run the light on 1x18650 instead of 2x18650. Although the effect is not huge, it is noticeable (i.e. unscrew one battery compartment tailcap and watch output drop slightly - reconnect the tailcap and watch it jump back up). It is not as noticeable on the Hi runtime above because I am using an IMR-18650 for the comparison 1x18650 run – but with standard ICR cells, you can see the drop when going down to 1x from 2x18650.
Even more interesting, this is NOT the case when you run it on a single emitter – 2x or 1x 18650 makes absolutely no difference in output.
So the dual circuits are clearly able to distinguish whether one or two 18650 cells are present – but the light responds differently depending on how many emitters are activated.
This is particularly interesting, as you can light up either emitter from a single battery in either well (i.e., each is emitter is not limited one specific battery well/circuit). The dual circuits are somehow able to compare the input sources in each well, and provide consistent power to whichever emitters are activated. This is pretty distinctive. It also suggests something of a backup feature – if one emitter/circuit were to fail, the other should be able to carry on from its dedicated cell.
In terms of overall performance on 18650, the light obviously lasts for a lot longer on 2x18650 than 1x18650. It is also somewhat more efficient to run both emitters at Med than it is to run one emitter at Hi, as you might expect.
Note an interesting feature here – the light shuts-off abruptly shortly after ~50% output is reached (i.e. some time after it drops out of regulation). The same occurred on my unprotected IMR-18650. This confirms the built-in low-voltage protection circuit feature in the DT-20, allowing you to safely use unprotected cells.
Let's see how it compares to other high-output lights on 18650:
The DT-20 is certainly efficient on Hi, compared to other lights that use multiple emitters. Med level efficiency also seems reasonably good for the number of emitters (although PWM lights are never as efficient as current-controlled ones).
And now compared to single-emitter XM-L lights on Hi:
Finally, on 4x CR123/RCR sources:
I don't have a lot data here, but you can see the 4x DT-20 typically matches the output and runtime of the 6x 4Sevens S18. This is due to the lower efficiency of the SST-90 emitter compared to multiple XM-L emitters.
The On/Off button and the mode-changing button are difficult to distinguish from each other. Due to the symmetrical nature of the light, you can only tell the difference by very subtle tactile or visual differences on the boot covers (or indirectly by the various labels on the body). In the dark, you are likely to confuse the two buttons (i.e., changing emitter number instead of output mode, etc.). It would be better if the mode-changing button were in a different location.
PWM is improved from the earlier Defier series, now at 1 kHz. But this is still visible to those who are sensitive to it (especially on Lo).
The electronic switch requires a standby current, but this was measured at a negligible 48uA on my sample (i.e. over 6 years to drain a single 18650 2600mA). Note screw threads are not anodized, so no tailcap lockout is possible.
There was some noticeable hum on the Med modes on my sample (and Slow Beacon, which shares the same output level). This is presumably due to inductor whine, which is very variable from sample to another.
Ergonomics are good on the light, although grip could be enhanced with some actual knurling.
Light gets warm quickly on max output. Something to keep in mind if you leave it tailstanding for awhile and then go to pick it up.
The light comes in a number of body segments, with screws holding the base and the head to the handle (e.g. like the Eagletac M2- and M3-series lights). Screws seem good quality (hex-head), and all were tightly fixed on my sample. But you should keep an eye on them to ensure they don't loosen with time, which could affect waterproofness.
The DT-20 is a distinctive light. While there are a few other dual-head options on the market now, single- and triple-emitter lights remain the norm. The DT-20 is remarkably compact for a dual-head light, with a surprisingly responsive dual-circuit design (i.e., it has an unusual user interface and battery control mechanism).
Let's start with the output – thanks to the ability to indepently control emitters, you have 6 constant output levels, 2 beacon levels, and 2 strobe levels (i.e., you can run either or both emitters, at all relative output levels). Note however that the Hi mode on one emitter is about the same as the Med mode on both emitters, so there aren't quite as many discrete levels as this might suggest. The Skilhunt ANSI FL-1 specifictions seem quite accurate for output and throw, at all levels. Runtimes also seem quite believable (note that I use lower capacity 2200mAh 18650 cells in my testing).
Compared to the earlier Defier series, I am happy to see the wider range of output level spacing (i.e., a lower Lo now). I am also glad to see they have raised the PWM from 200Hz to 1kHz for the Lo/Med modes. While this is still detectable by eye for those who are sensitive to it (especially on Lo), it is a great improvement. Oh, and the built-in low-voltage protection feature is a nice touch – you can safely use unprotected Li-ions in the light.
What I find particularly distinctive is how the light's dual circuits handle the batteries and emitters. Each battery well in the handle appears to have its own circuit (i.e., it is not like other lights where the wells are directly wired to one circuit, in parallel or in series). But this doesn't mean that one circuit controls one emitter independently - rather, the circuits are able to work together. For example, a single battery in one well can power either or both emitters, and dual-emitter (but not single-emitter) output dims slightly if only one battery is installed. It thus seems that the circuits can interpret whether one or two cells are installed, and respond collaboratively depending on the number of emitters engaged. I realize that these effects are probably irrelevant to the average user, but as someone who tests a lot of lights, it is always interesting to see something novel.
As for the interface, the switches are well-placed for easy access near the head. But I'm not crazy about their symmetrical location on either face of the light (i.e., you have to look carefully to figure out if you about to change output modes or turn On/Off). I personally like to see a lock-out mode on any light, to prevent the risk of accidental activation – and particularly on lights with electronic switches, which by their nature require standby drains. But in this case, the standby current is pretty negligible at under 50uA, so that is not really a concern (i.e., you have years before it would fully drain a battery).
I like the hand-feel overall - the light seems well-balanced. It is also remarkably compact - typically no larger than many side-by-side 2x18650 single-emitter lights (and in fact narrower than some). That's pretty impressive when you consider you get almost twice the max output on the DT-20, compared to single-emitter lights.
I'm glad to see Skilhunt has continued to expand beyond their original Defier series with the DT-20 - an innovative dual-head light with improved PWM and mode spacing. Dual-head lights are something an intermediate market when it comes to maximum possible output, but the DT-20 clearly slips into the lower size/weight class, while maintaining fairly high output. It is definitely something to consider if you want more power in a compact size.
DT-20 provided by Skilhunt for review.