# Sunwayman T21CS (XM-L U3 1x18650 2xCR123A/RCR) Rechargeable: REVIEW, RUNTIMES, BEAM+



## selfbuilt (Apr 16, 2013)

*Warning: pic heavy, as usual. *











The T21CS is a new offering from Sunwayman, in the rather crowded 1x18650, 2xCR123A/RCR space. What's distinctive about this light? Well, it comes with an in-light 18650 charger, and has a rather unique interface. Let's see how it compares to the competition …

*Manufacturer Reported Specifications:* 
(note: as always, these are simply what the manufacturer provides – scroll down to see my actual testing results).


LED: CREE XM-L U3
Runs on: 1 x 18650 or 2 x CR123A/RCR123A cells (NOT Included)
Working Voltage: 3~8.4V
Output/Runtime: Turbo: 600 lumens, High: 350 lumens/2.4 Hours, Medium: 75 Lumens/12 Hours, Low: 8 Lumens/104 Hours 
[_Reviewer note: There are only three modes – Turbo/Hi appears to refer to a single mode before and after step-down. See Runtimes for a discussion_]
Peak Beam Intensity: 24000cd
Beam Distance: 300m
Tactical tail switch interface coupled with side switch
Constant circuit maintains constant output
Built-in charging module charges li-ion 18650 battery (Does NOT Charge 16340 or RCR123A cells)
Smooth metal reflector
Aerospace-grade aluminum alloy production
Military Spec Type III hard anodized body
Ultra-clear tempered glass lens
Includes: Charger, Holster, O-ring, rubber cap, plug, lanyard
Dimensions: Length: 6" (153.8mm), Head Diameter: 1.8" (41mm), Tail Diameter:1.18" (30mm)
Weight: 5.75oz (163g) 
MSRP: ~$105






The T21CS comes in study packaging. Inside the cardboard box, there are two layers of cut-out foam. The top layer has the light, securely packaged. The lower layer has the holster (with a baggie containing the wrist strap, extra o-rings, and extra charging port cover), USB charging cable, AC adapter, manual, warranty card and product insert.













From left to right: AW Protected 18650; Sunwayman T21CS; Rofis TR31C; Nitecore MH25, P25; Eagletac G25C2-II; Olight M22.

All dimensions directly measured, and given with no batteries installed:

*Sunwayman T21CS*: Weight 161.9g, Length: 154mm Width (bezel): 41.4mm
*Eagletac G25C2-II* (stock): Weight 141.0g, Length: 150.6mm, Width: 39.6mm
*Eagletac TX25C2*: Weight 93.6g, Length: 120.4mm, Width (bezel): 31.6mm
*Klarus RS11*: Weight 158.0g, Length: 160mm, Width (bezel) 34.9mm
*Klarus XT11*: Weight 133.0g, Length: 148.8, Width (bezel) 35.0mm
*Nitecore MH25*: Weight: 145.4g, Length: 160mm, Width (bezel): 40.0m
*Nitecore P25*: Weight: 171.3g, Length: 160mm, Width (bezel): 40.0m
*Rofis TR31C*: Weight: 180.7g, Length: 153.0mm, Width (bezel): 39.8mm

Overall size and weight is in keeping with other lights with built-in 18650 charging options. Note that this typically adds a bit of length and weight, due to the extra circuitry and tailcap/body tube spacing needs.


























Anodizing is a very flat matte black, with no chips on my sample. This is different from the glossier natural finish that I am accustomed to with Sunwayman (and prefer, to be honest). Labels are bright white against the dark background. There is some limited knurling around the body tube, but it is of mild aggressiveness. Grip is not as high as it could be.

In addition to the tailcap forward clicky switch, there is also an electronic side switch in the head. Switch feels are about typical for both. Note that the functions of the switches are different from other lights I've tested – scroll down to the User Interface section for an explanation.

The T21CS comes with a crenaled bezel ring. It looks to be aluminum, like the rest of the light.

There is a spring on the positive contact point in the head, which means flat top cells can be used. Even with the inner sleeve (explained below), the internal body tube is wide enough to take high-capacity protected 18650 cells. 

Screw threads are square cut (i.e., trapezoidal), and seem of good quality. They are not anodized, as the threads are required for one of the current paths. There is anodization to separate the two current paths (i.e. the inner sleeve from the outer threads). This is all explained below.

Light can tailstand stably. Note there is an external switch retaining ring in the tailcap (black).

As mentioned above, there are actually two current paths for how the tailcap connects to the circuit in the head: 










The external path is illustrated by the red arrows above. Basically, there is a continuous connection between the switch spring and an outer contact ring on the switch PCB. This connects to a non-anodized portion of the tailcap base, which in turns connects through the non-anodized screw threads. As a result, you have a continuous standby connection as soon as you first start screwing on the tailcap. Clicking the switch has no effect on this current. This connection is what allows the electronic switch in the head to draw power and operate (and, I presume allows charging of an 18650 inside the light). 

The second connection path is carried by the inner metal sleeve of the body tube. This sleeve has a non-anodized portion that makes contact with the raised brass ring on the switch PCB (blue arrows above), only when the tailcap is fully tightened. This current path is under control of the switch – you can break this connection by clicking the switch off, or loosening the tailcap a quarter turn. 

See the interface discussion below for the unique way Sunwayman has designed the interface.






















The charging dock uses a standard 12V DC pin-style connector, under a removable red plug (USB charging cable and USB-AC adapter included). Since this plug is not attached, I would be worried about losing it (note that a spare is provided with the package). 

There is a LED indicator on the light, which tells you the charging status when the charger is attached. When charging, the LED will flash red at a slow rate. When fully charged, the LED will switch to constant green.

The AC adapter for the included USB cable list a maximum charge rate of 600mA, which is higher than the standard USB 2.0 specs (which limit you to 500mA charging current). From my testing, when connected through just the USB cable to a computer, the charging rate was 5 hours and 15mins for my 2200mAh 18650 cells. When plugged into AC power through the adapter, the charging rate dropped just over 4 hours. 

This accelerated charging on AC power is similar to the time it takes my Pila IBC charger to charge these cells. It is certainly faster than most of the other USB-only in-light 18650 chargers I've tested (typically, ~6-7 hours). Resting voltage for the cells was a fairly consistent ~4.19V, which is appropriate.










Reflector is basically smooth, and fairly deep. There seems to be some fine texturing of the reflector, which shows up as reflected rings and a slight haze (likely to smooth out the beam). There is an anti-glare coating on the lens. The XM-L (cool white) emitter was well centered on my sample.

*User Interface*

The user interface of the T21CS is unique in my testing - this is possibly the first time that I've seen a light where the state of the tailcap clicky switch causes different behavior of the side switch. I find that it is not described in sufficient detail in the manual, so I will go through it in some detail here.

First, a general comment – "Turbo" and "Hi" refer to the same thing, the max output mode of the light (with supposed timed step-down from Turbo to Hi). See the Runtimes section below for a discussion.

_With the tailcap switch clicked "Off"_ – "Dimming Mode 1" (default)

Due to the constant current path as soon as the tailcap is screwed on, the side switch can activate the light by a simple press. 

Turning on the light by the side switch brings you to Turbo output. Repeated clicking of the side switch advances you through all the modes in the following sequence: Turbo > Med > Lo > Standby Off, in repeating loop. In essence, the light defaults to Standby Off as soon as the tailcap is screwed on, and a single click of the side switch advances you to Turbo. There is no memory mode – the light always follows this sequence.

Double-clicking the side switch when "on" this way gives you a regular strobe mode - Sunwayman call this the "hidden strobe". Double-clicking a second time gives you a SOS mode. Double-clicking a third time brings you back to the regular "hidden" strobe mode. A single click restores you to the constant output modes. See oscilloscope traces below for more information on these modes.

To turn the light "off" by the side switch in this default "dimming mode" method, you need to cycle down to Standby.

_With the tailcap switch clicked "Off"_ – "Dimming Mode 2"

Sunwayman provides an alternate way to use the side switch to control modes. By default, the switch works as described above. But instead of repeated clicks, you can program the light to change modes by a press-and-hold of the side switch. 

To change to this "Dimming mode 2", turn the light "on" at the tailcap switch. Press and hold the side switch for 2 secs, release, and immediately hold again for another 2 secs. The light will flash quickly to let you know the side-switch control mode has changed. Click the light "off" at the tailcap.

Now, turning the light on by the side-switch is the same as before – click on the side switch to get Turbo. But clicking the side switch again jumps you to Standby Off. Click again brings you back to Turbo. To access the lower constant output modes, _press and hold_ the side switch. The light will cycle from Turbo > Med > Lo > Standby Off. Simply release the switch to have light stay on in the desired mode. Strobe and SOS are accessed as above by double-clicks.

Personally, I find this secondary "dimming" mode more intuitive – but memory of selecting it doesn't survive a battery change on my sample. If you swap out the battery, the light returns to the default "Dimming Mode 1".

_With the tailcap switch clicked "On"_

The T21CS also has a forward tailcap clicky for dedicated "tactical" functions. 

At any point, you can press it for immediate Turbo output (i.e., press for momentary, click for locked on). It makes no difference what state the light is in from the side switch - clicking the tailcap switch forces you to max output.

One of the unusual features of having the tailcap switch clicked on is that you now lose the ability of the side switch to advance you through regular output modes. Instead, pressing the side switch will gives you access to two new strobe modes - a "police strobe" mode and "slow strobe" mode, to use the Sunwayman terms. You access the "police strobe" - where the light alternates between periods of dark and rapid flashes - by a single click of the side switch. You access the "slow strobe" by a double-click of the side switch. See the oscilloscope traces below for more information. Press the side switch again to return to Turbo.

To restore the full range of output level control, you need to click the light "Off" at the tailcap switch. The light returns to the previously side-switch-set light output mode.

If you find the above confusing, please refer to my video below. :wave:

*Video*: 

For information on the light, including the build and user interface, please see my video overview:



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. 

As with all my videos, I recommend you have annotations turned on. I commonly update the commentary with additional information or clarifications before publicly releasing the video.

*PWM/Strobe*

I didn't see any evidence PWM at the Med or Hi levels, but there was a non-visible reoccurring signal on the Low mode:






Judging from its appearance – and the lack of concomitant signal on Med – I think this is some sort of circuit noise on Lo. At 1.48kHz, this signal frequency is above the visual detection threshold, so you won't see it. The intensity is high enough that you may be able to faintly detect it when shining on a fan, though.

There are two sets of blinking modes available on the T21CS – "hidden strobe" and SOS, accessed by double-clicks from the side switch with the tactical tailcap in the Off position, and "police strobe" and "slow strobe", accessed by a single-click or double-click, respectively, of the side switch when the tailcap is in the On position.

Regular "hidden strobe":





The regular strobe is fairly typical fast "tactical" strobe, of 12Hz frequency.

If you double-click again in the regular strobe, you get a fairly typical SOS mode:






Tactical switch "police strobe":









This "police strobe" is rather unusual – I have definitely not seen anything like it before. You get four rapid pulses at 15.7 Hz (blow-up provided in the second trace above). This takes ~0.25 secs, followed by ~1.25 secs of no light, in a repeating pattern (shown in the first trace above). 

This periodic strobe is mildly annoying, but I don't really see how useful it could be to anyone in a "tactical" situation (i.e. it is less disorienting than the regular strobe mode above). :thinking: I'm guessing it's intended as a more signaling strobe, to direct traffic, etc..

Tactical switch "slow strobe":





The slow strobe is an oscillating 1 sec on, 1 sec off flash of the light.

As an aside, I find it somewhat odd that the debilitating strobe is part of the main side-switch sequence (i.e., the "hidden strobe"), but that the slow and intermittent signalling strobes ("slow strobe" and "police strobe") are part of the "tactical" tail switch mode.

*Standy Drain*

Whenever the tailcap is in contact with the body tube and battery, there is a constant standby current. I measured this current on 18650 as 1.65mAh. For a 2600mAh 18650 battery, that would translate into 65 days before it would be fully drained.

Unfortunately, there is no physical or electronic lock-out mode on the T21CS. As a result, expect your batteries to last less than 2 months while inside the light. 

*Beamshots:*

For white-wall beamshots below, all lights are on Max output on an AW protected 18650 battery. Lights are 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.





























































Beam pattern and overall output is certainly in keeping with the other in-light 18650 charging models shown above. Throw is reasonable for the class, about the same as the Rofis TR31C (but less than the Nitecore P25). Scroll down for detailed comparison testing results.

*Testing Method:* 

All my output numbers are relative for my home-made light box setup, as described on my flashlightreviews.ca website. 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. Please see http://www.flashlightreviews.ca/FL1.htm for a discussion, and a description of all the terms used in these tables. Effective July 2012, I have updated all my Peak Intensity/Beam Distance measures with a NIST-certified Extech EA31 lightmeter (orange highlights).
















The first observation above is that the T21CS is brighter on 2x battery sources than 1x (e.g., like the Klarus XT11). But there are additional differences between how these modes operate (i.e., timed step-down only on 2xRCR). See runtimes below for more information and a discussion of relative output levels.

Sunwayman ANSI FL-1 specs seem over-stated for throw, as my direct beam intensity measure on 1x18650 (18,500cd) is lower than what they report. I have also tested the light on 2xRCR (not shown in the table above), and got 21,700cd, which is still lower than their reported 24,00cd. In any case, the throw for my T21CS is still quite good for the size and relative output levels.

*Output/Runtime Graphs:*
























As previously mentioned, the T21CS is brighter initially on 2xRCR or 2xCR123A. Runtime patterns are different however, with an apparent timed step-down only on 2xRCR (but not 2xCR123A or 1x18650), after 5 mins. The light is typically fully regulated, except on Turbo with 1x18650, where you see a semi-regulated runtime pattern on Hi (i.e., direct-drive-like). 

As a result, it seems that the specs are bit misleading in this regard - Sunwayman reference to the "Turbo" and "Hi" modes appears to refer to the before and after stepdown, but only the 2xRCR actually steps down. 

To summarize the output results: 1x18650 only shows a "Turbo" of 620 estimated lumens (no step-down), 2xCR123A only shows "Turbo" of 750 estimated lumens (no step-down), and 2xRCR shows an initial "Turbo" of 740 estimated lumens with a timed step-down to "Hi" of 480 estimated lumens. :wave:

Note that on the fully regulated modes (i.e., all modes except the semi-regulated Turbo 1x18650), there is step-down to Med and/or Lo as the batteries near exhaustion. This is a nice feature, and one that I would like to see more often (i.e., as opposed to a complete shut-down). :thumbsup: The semi-regulated Turbo 1x18650 doesn't need defined step-downs, as the gradual drop-off accomplishes the same effect.

Overall efficiency is good on all batteries, consistent with a typical XM-L based current-controlled light. ANSI FL-1 runtime specs are believable for 1x18650 (recall that the FL-1 standard is for runtime down to 10% of initial output, and most manufacturers use higher capacity batteries than my AW 2200mAh cells used here).

*Potential Issues*

The user interface is unique, and has a few unusual features. The main issue for me is that the function for the side switch depends on the status of the tail switch. Many times during testing, I would forget which switch had been pressed first (or last), and wound up strobing myself trying to change output levels.  This is because if you turn the light on by the side-switch (comes on in Turbo), and then subsequently press the tactical tailcap switch, nothing apparently happens (i.e., you are still in Turbo). But now if you press the side switch again, you now get the "police strobe" instead of Medium. In other words, when in Turbo, there's no way to tell if the tail switch is in the On- or Off-position until you press the side switch and see what happens. See my video overview for more information.

The "police strobe" mode seems to be more of an unusual signaling strobe than a tactical one. I find to be less distracting than the regular "hidden" constant frequency strobe (which is not available if you are in the tactical tail switch On mode).

Standby current is rather higher at 1.65mA, which will drain typical cells in about two months. There is no way to physically lock out the light, and there is no electronic lock-out provided. As a result, you will need to recharge your batteries frequently.

The charging port cover is fully removable, and could potentially be lost during charging cycles. Sunwayman provides an included replacement plug, however.

The side switch is difficult to locate by touch or sight, as the charging port cover actually stands out more.

My review sample suffered from a physical failure that prevented reliable operation of the Tactical tail switch control mechanism. The problem was that the inner sleeve slowly separated from the body, preventing contact as it slightly slid down the inside body (due to pressure from the tail switch, pushing it away). Sunwayman traced the issue back to a residue on the inner sleeves of some of the early pre-production review samples that prevented the glue from fully bonding to the body of the light. Sunwayman assures me that this was a limited case to a couple of the pre-production units, and has been resolved going forward on the production runs. However, it does illustrate a potential longer-term concern, as you are dependent on the glue successfully holding the inner sleeve to the body (in spite of ongoing pressure from the tailcap).

*Preliminary Observations*

I have been reviewing a lot of 1x18650 in-light charging solutions lately. This is the first model I've tested from Sunwayman, and it shares many of the same potential benefits (and limitations) to others using this approach - along with a few novel twists.

As a 1x18650-class light, the T21CS does what you would expect – it has a reasonable number of modes, decent throw and output for the size, and support for multiple battery configurations. There are some output and runtime pattern differences (depending on battery source), but overall efficiency is good - certainly consistent with the typical XM-L-based, current-controlled lights of this class. One thing I really like here is the brief step-down to Med/Lo on the regulated modes before the Li-ion protection circuits cut-off. :thumbsup: 

The ability to charge an 18650 inside the light is a bonus, and the charging solution worked well in my testing. Charging directly through a USB port is faster than most other lights I've tested (5 hours 15mins for my 2200mAh 18650), and it can be charged even faster with the bundled AC adapter (~4 hours). The cells were consistently charged to a reasonable level (i.e., ~4.19V in my testing).  Note that the light uses a custom USB-DC connector cable instead of a standard micro-USB cable and port.

So what's the problem? Well, like a few lights that use a similar two-current path approach (e.g., Klarus RS11), there is a constant standby mode that cannot be locked-out. In the case of the T21CS, this is high enough to fully drain a standard 18650 in two months. :sigh: 

That said, the two-current path approach does allow you to become more creative with the user interface design. Unfortunately, I find some of the choices made in this case to be non-intuitive. While it's great that a tailcap press or click will jump you to max output, the fact that it changes the behavior of the side switch means that you can't always predict what will happen next (i.e., pressing the side switch will move you to Med or "police strobe" depending on the state of the tail switch – which you cannot always tell ahead of time). I also find it odd that the signaling strobes are associated with the "tactical" tailcap, whereas the debilitating fast strobe is in the regular control set (i.e., you cannot access the classic "tactical" fast strobe when the "tactical" tailcap is switched on). :thinking:

These tailcap interface quirks aside, I do like the regular side switch interface – especially the option to choose between a repeated-click or press-and-hold control scheme. Unfortunately, memory of your control scheme choice is lost when you break the current to change the battery. But either way, the side switch interface performs as you might expect for a general purpose/tactical light (i.e., Turbo first, without memory, and strobe hidden behind a double-click).

Output and beam pattern is about typical for a light of this class and size, with good throw. 

At the end of the day, the Sunwayman is another option to consider in the in-light 18650 charging class. It has some commendable points, but l would encourage Sunwayman to reconsider some aspects of the "tactical" tailcap switch user interface. As always, I leave it up the user to decide what is best for their usage pattern and needs. Hopefully the results and review are helpful in that regard. :wave:

----

T21CS was provided by Sunwayman for review.


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## holylight (Apr 16, 2013)

*Sunwayman T21CS (XM-L U3 1x18650 2xCR123A/RCR) Rechargeable: REVIEW, RUNTIMES,*

Tks for the good review. Hardly any single cell flashlight (14500,16340) can beat v11r till now. Sunwayman goto bring back the v11r aura.


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## kj2 (Apr 16, 2013)

*Re: Sunwayman T21CS (XM-L U3 1x18650 2xCR123A/RCR) Rechargeable: REVIEW, RUNTIMES,*

Thanks  was really waiting on this review 
Is that "tactical" strobe not the Police Strobe as Sunwayman calls it?


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## selfbuilt (Apr 16, 2013)

holylight said:


> Tks for the good review. Hardly any single 14500 or AA flashlight can beat v11r till now. Sunwayman goto bring back the v11r aura.


Yes, the V11R remains one of favourite EDC lights. 



kj2 said:


> Is that "tactical" strobe not the Police Strobe as Sunwayman calls it?


Yes, that is what Sunwayman calls it. They differentiate it from what they call the "hidden strobe" (which I refered to as the regular strobe above). I will edit my review post to use their official names for these two modes, to avoid any confusion.


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## tobrien (Apr 16, 2013)

yeah that red plug is gonna get lost in a second with most users. I guess there isn't truly any graceful or aesthetically pleasing way to attach it on there though


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## holylight (Apr 23, 2013)

In my signature below comparison, v11r give the best white beam with no obvious contrast of rings. The beam is same or not more brighter than sc52 ( I am very impressed with this light). Now the sunwayman charging system need to improve to usb type or do away with with the charger. Than I buy another sunwayman


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## selfbuilt (Apr 24, 2013)

tobrien said:


> yeah that red plug is gonna get lost in a second with most users. I guess there isn't truly any graceful or aesthetically pleasing way to attach it on there though


Yes, although most makers have opted to permanently attach the plugs in some way (which generally makes them more prominent, though). The end result is often that the charger plug is more easily identified by touch or sight than the side switch (which I find is the case here too). :shrug:

Some makers (like Nitecore on the MH-series) have opted for a metal screw-down cover (with o-rings for waterproofness). But it's difficult to verify the o-rings are there, since they are not visually apparent. One interesting solution is the Rofis TR31C, which doesn't use a plug cover at all - apparently, they have somehow waterproofed the connector socket (based on preliminary evidence in a video from a dealer who tested it). I suppose it is possible to pot the connector in some way, but of course that isn't accessible to end user to verify.

No perfect solution yet for an in-light charging feature, I guess.


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## kj2 (Apr 24, 2013)

selfbuilt said:


> No perfect solution yet for an in-light charging feature, I guess.


Klarus does a good job with their magnetic charging connection


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## selfbuilt (Apr 24, 2013)

kj2 said:


> Klarus does a good job with their magnetic charging connection


Yes, that is a good body design for a charging port at the tailcap (as there is no open voltage or exposed entry). However, the dual-circuit design means that PWM is used. I recommend people check out my review of that light for a more thorough discussion of the magnetic charging cable design.


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## kj2 (Jun 13, 2013)

After reading and watching your review again  I noticed that the holster is somewhat to small for the light. The hard-velcro-part can touch the flashlight, which can cause scratches. 






Now, I don't know if you use the light and holster much- but if you are using it (a lot), are you noticing some marks on the HA-III coating?


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## selfbuilt (Jun 13, 2013)

kj2 said:


> After reading and watching your review again  I noticed that the holster is somewhat to small for the light. The hard-velcro-part can touch the flashlight, which can cause scratches.


Interesting observation, I could see that would be possible. I haven't noticed, as I have not been using the light.


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## kj2 (Jun 13, 2013)

selfbuilt said:


> Interesting observation, I could see that would be possible. I haven't noticed, as I have not been using the light.


Have this same problem with the Fenix TK21 holster. Because of that, I use a Maxpedition holster now for that light.
I can imagine you can't use all the lights, manufacturers send you for review


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## tubed (Jun 13, 2013)

I own a Nitecore MH25 and love the self-charging ability but that light has some limitations (the low setting mostly). Thought this might be better but...... 
what blows me away is that they make a light with that much complexity in the UI and do not give it the ability to come on in low (unless I missed something). It seems anyone who follows this forum even a little would know that that is a very common desirable trait. Instead, they use the complexity to add addtional strobe modes (??) Are there really a lot of folks out there wishing they had more strobe functions on their lights?
Light makers (IMHO) seem to have this incredible knack for making a really good light and then just screwing up one key (simple) thing, that diminishes it greatly. 
Thanks for the great review.


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## evolution80 (Jun 24, 2013)

^ i hope there is some way to allow this model to come on in low - i just ordered one along with a nitecore srt7 - should arrive today - 

i am not so sure about the complex user interface too 

i wonder what the main difference between the t20cs and the newer t21cs is? i figured the t21cs can be used in 600 lumen mode with a 2.2 hour runtime? also more aluminium (heavier) means better heat absorption? :thinking:


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