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Thread: Object/Subject Review: XTAR S1 (3xXM-L U2)

  1. #1

    Default Object/Subject Review: XTAR S1 (3xXM-L U2)

    XTAR is a Chinese company that makes not only great flashlights, but batteries and chargers as well. The S1 is XTAR's entry into the large, 3xXM-L class, designed for high output and long throw. The highlights for the S1 are it's control ring interface with customizable brightness preset, and an innovative battery contact system to hold many lengths of "18650" batteries.

    Thanks to for lending the S1 for review.

    I’ll be reviewing the S1 in two sections: first, I’ll discuss the light objectively (the facts about the light itself), then I’ll discuss the light subjectively (my impressions about the light's performance when used for specific applications). With three XM-L U2 emitters and a large deep reflector, this is a large class thrower, and I'll review it as such. XTAR's website currently (11.14.12) lists the S1 as a "Rescue Flashlight" and "coming soon." If you have any other specific applications you'd like the light tested for, let me know and I'll see what I can do.


    Here are the specs on the S1:


    LED: 3x Cree XM-L U2
    Battery: 3x18650/18700 Li-ion
    Working Voltage: 2.7-4.2V
    Output: min. 30lm, max. 2750lm
    Runtime: 1h (2750lm)
    Max range: 359m
    Max Intensity: 32300cd
    Switch: Head magnetic ring switch
    Mode: SOS/Strobe/High/Off/Preset/Select
    Water resistance: IPX-8 standard
    Impact resistant: 1m
    Size: 83mm (head), 47mm (body), 240mm (length)
    Weight: 956g (excluding batteries)

    -3X CREE XM-L U2 LED, independent driver for each LED
    -a leading design for output customize
    -Max output 2800lm
    -Unique design at the negative pole



    My review sample came in a plain cardboard box, wrapped in a little foam wrap. I'm under the impression XTAR is planning some sort of special packaging for the retail version, based on the post they made here:

    Construction Quality

    This light has heft. When you hold it, it exudes a feeling of solidity that makes you confident it will hold together. A closer examination shows that the
    S1 is indeed a very well-made light.

    Here's close-ups of each section of the light, and a shot of the whole thing disassembled:

    Good attention has been paid to detail and style on the S1. The head has some shallow cooling fins to help disperse heat into the air, but in my use I found that the sheer size of the head keeps it from getting too hot. Later, with the shots of inside the head, you'll see the design moves heat from the emitters to the body very well. Beneath the cooling fins is the control ring.

    The ring itself is slanted with small circles cut into it for your fingers, with a symbol indicating its rotating selection nature to point to the mode you are currently on. Above the ring are printed the labels for the different modes you can select. The S1 has detents for each mode, so you can feel it "click" into place. I'll note here that there are no stops on the ring, so you can actually rotate the selector ring all the way around the head, and there are regular detents all around. At any position other than the labeled modes, the light will be off.

    Also, I found the grip on the control ring to be difficult, the circles cut are not very deep, and the ring is angled.

    The body of the S1 has medium knurling, with smooth grooves cut into it for your fingers. There is also a large grip/anti-roll ring built into the tail cap, which is not removable. Three of the six protrusions here have small holes where you could attach a lanyard, though no lanyard was included with my review sample. The tail cap itself if very agressive, with six truncated-pyramid protrusions several millimeters tall. The are evenly spaced, so the S1 can tailstand well. With all the grip, the tail cap is easy to get on and off for battery changes.

    The body has the XTAR logo printed on a flat section of one side, and the model name on the other.

    The S1 implements 3 emitters in one head, so the reflector is actually the shape of 3 reflectors merged together. The emitters seem to be well-centered, and the reflector and lens came free of any debris or grime.

    Here you can see how the inside of the head is designed. Three holes at the base of the reflector fit over the three emitters, which are in small plastic circles with slightly raised rings to keep the reflector in place. The reflector is not threaded, but is pinched in place between the lens and the head when you put the lens and bezel on. Because the reflector is removable, you can take it out and use the light in "candle mode" for a lot of flood instead of through. However, this leaves the emitters unprotected (the lens won't stay firmly in the head without the reflector) so this is only for flood light in a pinch, and probably not condoned by the manufacturer. Also, not that the reflector is smooth, not textured. This will give maximum throw, with a less smooth beam profile.

    The threads on the head are small, but they are squared and anodized, so they should hold up well. There's really no reason to be taking this on and off often anyway.

    You can see here that the rear of the head has a large cylinder of whit plastic that is inserted into the body when you put them together. The threads here are non-anodized, which means they'll wear a little faster, but they will have a better electrical connection.

    The body is made to house the three batteries snugly, with no need for a flimsy battery housing.

    The threads on the tail are squared an anodized. This means that slightly loosening the tail cap will lock out the light, which is good to do if you won't be using the light for a while but want to leave the batteries in it. You can also see that there is an interesting tail cap design to handle the three 18650-18700 batteries.

    To make contact with the batteries, a circular metal plate is on the head for the positive contact, and three spring-loaded pistons are at the negative contact. The pistons for the negative contact ensures that you'll have good connection there for a wide range of battery lengths, they move up and down and also the three of them together spin freely as a unit to keep in line with the batteries as you screw the tail cap on and off. The metal circle for the positive contact might have trouble making contact with flat-top cells. I also found it to be loose on my review sample, I'm not sure if that is intentional or not. It will turn a little bit, but then kind of slide back--it feels like wires connected to it twist when you move it and pull it back when they untwist. This is the only point of the construction quality I'm concerned about failing.

    The function of the battery connections is a little hard to describe, so I'll illustrate it in the video. This shows how the positive contact plate rotates a little bit, the negative contacts rotate freely and are spring-loaded, and also shows how the control ring can be rotated all the way around with no stops.

    User Interface

    One of the highlights of the S1 is the simplicity of the UI. By using a control ring, XTAR has eliminated the need to remember clicking combinations or the like. All you need to do is turn the ring so that the marker on it points to the mode you want.

    Six modes are available (as labeled, from left to right): SOS, Strobe, High, 0, Preset, Select. 0 is actually off, and turning the ring past SOS to the left of past Select to the right will also turn the light off. The Preset-Select system is very simple, but not everyone figures it out right away. Turn the light to Select, and the light will start to ramp up and down between maximum and minimum brightness at a moderate speed. When it reaches the brightness you want, switch from Select to Preset, and you'll lock in your choice for brightness. You can then go to Off, high, Strobe, or SOS, and still be able to come back to Preset for the same brightness that you chose. The S1 will remember your desired brightness at Preset until you move to Select again, or the tail cap is loosened. After loosening and re-tightening the tail cap, Preset will automatically be set to a default brightness.

    Here's a video showing the UI of the XTAR S1:

    Action Shots

    Light in Hand

    I found that I needed at least two fingers to use the control ring, so the pictures is taken like that, even though it's slightly uncomfortable.

    Tail Standing/Candle Mode

    White Wall Beam Profiles
    (ISO 100, f/6.3, 1/8")
    (From High to the lowest I could get on Preset)

    Indoor Shots
    (ISO 100, f/3.3, 1/4")
    (Control, Ceiling Bounce)
    (Default Preset, High)

    Outdoor Shots
    (ISO 100, f/3.3, 1")
    (Control, High)

    (This 4th scene is the same as the 3rd, but zoomed in on the building at ~150 yards)

    Long Range Shots
    (ISO 100, f/3.3, 1", exposure adjusted identically for each shot to match real appearance)
    (Control, High)

    (A zoomed-in version of the previous shot)


    The S1 claims impact resistance and water resistance. I did not test these claims, because the light was only lent to me for review, and I want to be sure to return it in working condition

    The S1 uses PWM (pulse-width modulation) to control the brightness. In normal use, I can't detect it in the beam, but I can see it on lower brightnesses when looking at the head and moving it quickly. There is no audible whine or buzz from the PWM. However, in Select mode, when choosing the brightness, the PWM is very noticeable even in the beam at lower brightnesses. This means that while selecting your brightness, the light will appear to flicker rapidly as it dims, then when you move back to Preset to lock in the brightness the flickering will stop.

    The S1 also has a "soft start", which means when you turn it on the brightness will seem to quickly ramp up to the mode you've selected, either High or Preset, instead of being instantly that bright.

    The S1 has a max current input of 4.2V, so it cannot use CR123 or 16340 lithium ion cells in series. Only use 18650 or similar sized cells in this light.

    Current Draw

    These measurements are made at the tail cap within a few seconds of turning on the light with fully charged batteries.

    3x18650 Trustfire 4.2V ICR
    High: 3.101 A
    Preset Max: 3.724 A
    Preset Default: .544 A
    Preset Min: .027 A
    Standby: 952±2 µA

    Note on the Standby current: If you have the batteries loaded and the circuit connected (ie. the tail cap is fully tightened), and the ring in the off position, there is a small standby current of <1 mA. With that current, you'd drain a set of three 2400 mAh batteries in approximately 315 days. That's not a horrible standby current, but you will want to remember to slightly loosen the tail cap when you're not using the S1.


    Note: The vertical axis of these charts represents a relative brightness measurement using a home made light box. The horizontal axis is time in hours:minutes:seconds. Runtimes are stated in hours:minutes. Each of the graphs are truncated to show the relevant portion of the data.

    Each of these tests was conducted with three fully charged 2400 mAh Trustfire 18650 protected cells. The first graph is for High mode. I've also run tests on Preset mode, set to a few different brightness levels. The last graph is for Select mode, to show how the output ramps while you're selecting the brightness to choose for Preset mode.

    You'll see that High and Preset modes have a bit of regulation, but not much, so the output is held near the original brightness for a while, but is by no means a constant output. After a time, the output drops off, and the PWM gradually becomes very noticeable, to the point where it is just flickering dimly at the end.

    High (Truncated to show detail)

    Time Regulated: 0:57:22 (approximate)
    Time Until 50%: 1:01:53
    Total Runtime: 12:35:40

    Preset, About 55% of High (Truncated to show detail)

    Time Regulated: 1:03:48 (approximate)
    Time Until 50%: 1:11:39
    Total Runtime: 7:43:32

    Preset, About 39% of High (Truncated to show detail)

    Time Regulated: 2:21:54 (approximate)
    Time Until 50%: 2:18:46
    Total Runtime: 18:32:33

    Preset Default, About 5-9% of High (Truncated to show detail)

    Time Regulated: 8:36:40 (approximate)
    Time Until 50%: 10:08:15 (50% of starting brightness)
    Total Runtime: 34:01:36

    This is for the brightness that is the default for when you first go to Preset after tightening the tail cap, before you go to Select. As you can see, the brightness actually increases over time in steps, then drops off. The starting brightness is about 5% of High, and the max brightness it reaches is about 9% of High. I can usually use Select to get to a slightly lower brightness, but not much lower.

    Mode Comparison (Truncated to show detail)

    Select (Truncated to show detail for a single, average cycle)

    Time for full cycle: 14.2 seconds

    This is the time from high to high or low to low, averaged over many cycles. The actual cycle is probably more smooth than my graph shows, but my equipment only has a max resolution of 1 hz. From this data, it does seem pretty certain that the ramping is linear, instead of any sort of logarithmic or "visually linear" pattern.

    Subjective Review


    The XTAR S1 is a very impressive light in 3xXM-L class, and the only one I know of that has infinitely variable output (at least so far). I find myself leaving it by the door so that it's available when I want to step outside, but I don't carry it in a pocket. I've heard rumor of XTAR including a holster for the production version. A holster would be a good idead to have for this light, because it's much too large to carry in a pocket or always have in your hand, but even with a holster I doubt I would just wear it around at night. This is a light that you take with you when to plan to definitely use it, otherwise it just takes up too much space and weight.

    My impression is that XTAR is waiting for comments on this first sample run of S1's to make tweaks to the model before they go into production, which is probably a good idea for a smaller company looking to make a big, high end, probably high cost light. So, the production model will most likely be at least slightly different than the model I tested.

    Here's some things I liked about the S1:

    +great grip on body and tail
    +bright, good use of U2 bin
    +solid construction
    +great negative battery contact and battery housing
    +smooth reflector, with great beam (good spot and spill ratio)
    +good UI

    A note on the beam, it looks pretty lumpy around the edges when you do white wall hunting, and even in outdoor use you can still tell it's got three separate reflector sections, but it throws great, and I like the balance between spot and spill. The spot could be ever so slightly tighter, but right now I really like the beam pattern. They've made the head very big, and used the space well to put three big reflectors in it.

    The UI is really nice for this. I like that High is always available easily, that's a very handy feature. The Strobe and SOS are available for people who like to use those, but for me, I just like having them out of the way, so it's easy for me to avoid them. I had very few accidental activations of Strobe, which makes me very happy . The Preset and Select system is a good way to implement ramping that we've seen before. I do wish that the ramping pattern were a little different, but I'll get to that. Overall, great UI, a pleasure to use.

    I really like the way the battery compartment has pistons to make contact with the negative ends of the batteries. In theory, you could use cells of different sizes in here and have them all make contact, but I wouldn't recommend that, because it's important for you battery capacities and discharge rates to match. Putting batteries in and out is pretty fluid with this setup, which is very nice. This pistons should provide some impact resistance for S1, though as I mentioned earlier, I can't test this light for impacts because it's a loaner. I also really appreciate that the battery holder is designed into the body of the light, so it's super-solid, and not a removable battery carrier. The plastic ones especially, but even some of the metal ones, always seem flimsy and fragile to me, so I'm glad for the solid feel of a huge hunk of metal here . The only disadvantage I can think of to this setup is that in some lights it might conduct more heat from the emitter to the batteries, but in the S1 heat hasn't been an issue for me because of the large mass and surface area.

    Here's a few areas that I'd like to see improvement in for the production version:

    -markings might wear off
    -poor grip on on control ring
    -PWM flicker on Select mode
    -"0" instead of "Off"
    -might need magnetic spacers to use flat-top cells.
    -hard to get to minimum brightness

    The biggest change that needs to be made to the S1 is the physical design of the control ring. The slanted nature of it, combined with the shallow grip, makes it tricky to change modes, especially with only one hand. Something needs to change here.

    I would also recommend finding some different way to mark the modes on the S1. As it is, I'm worried that they might wear off over time, and it's impossible to read in the dark. Maybe some sort of raised lettering or marking would be helpful. It wouldn't be as big of a deal if the ring was confined to working modes, but it can also go to any number of off positions outside of the modes, and you wouldn't know it. Also, it seems silly to spell out all the full names of the other modes, and then to print "0" instead of "Off".

    Also, with the positive battery contact being a flat circle, flat-top cells probably won't be able to make contact here. I'm not sure how this would be fixed with the current design, but it might be worth permanently attaching the head to the body in order to be able to have springs or some sort of raised contact here. Otherwise, I'd suggest XTAR include three magnetic conductive spacers as accessories.

    The last thing: it's hard to get to the minimum brightness, or much of the lower brightnesses. The Select mode doesn't spend much time on the lower brightnesses, so it's hard to get to from there. You can get fairly low with the Default Preset by loosening then tightening the tail cap, but this isn't the lowest low available. I'd recommend making the Default Preset for the production version be the minimum brightness.

    Overall, a great light so far, and I'm excited to see the improvements XTAR makes.


    XTAR made a lot of good decisions that help the S1 throw it's lumens like a pro, however, it's not solely a thrower. The S1 has a high output, they didn't skimp on the head/reflector size, each emitter has it's own parabolic section of the reflector, and the whole reflector is smooth (instead of textured) and very reflective for maximum throw. The parabolas for each emitter overlap a bit, but there is even a "spike" (I'm not sure how well you can see it in the pictures) that comes up between the emitters, to catch the few photons that might try to escape that direction. The S1 can throw impressively far. However, as I mentioned, it's not solely a thrower. I find that in practical use, the hot spot is larger and the spill brighter than one a light designed solely for throw. My own opinion is that this is a good thing, especially seeing XTAR advertise this as a "Rescue Light," which would need a medium sized hot spot and good spill, instead of a tight hotspot and minimum spill that you'd aim for if you just wanted a thrower.

    So, in short, the S1 will most likely fulfill your need for throw by sheer force of lumens, though it isn't optimized for it.

    Rescue Light

    XTAR's website advertises the S1 as a "Rescue Light". So, my impression is that they want to sell it to people who do search and rescue operations as part of their job. This isn't really part of my job, nor is it something I do often (at least in the intended sense), so I'm not able to do a 1st hand review of the S1 for search and rescue applications. However, I'll do my best to speculate based on what I know of search and rescue operations, and what I have experienced of the S1. (If I have time before returning the light, I'll have a friend go hide in the woods at night and I'll try to find them. )

    The performance of the light is very good for SAR (great high output, great throw), but I'd like to see a few changes. Number one: the control ring. It really needs to be either not slanted or have the grip improved, as I wouldn't want to be fumbling with the ring while someone's life is on the line. The Strobe and SOS are good features for SAR, so that's a plus. As I've mentioned before, I'd like easier access to low modes, and I think for SAR this is even more important. You probably don't need high output all the time (though quick access to it is good), and having maximum runtime is important when you don't know how long you'll be using the light. The quick battery change ability is plus, for when you do run out of power. Ideally, a good SAR light would have a charging dock so you could just set it down when done, and have the batteries be charged and ready when you need it next, but I know that would be a lot of extra R&D, so it probably won't happen for the S1. I'd also like to see a holster in the production version, including a clip at the top and bottom. This isn't the kind of light I'd keep on my hip with a belt, but I'd rather attach it to my backpack and use the holster more like quiver, pulling it over the shoulder, because the light is so bulky. My initial thought is that it would be nice if the S1 had the ability to accept primaries as well (6xCR123) so that you could have some on hand when you needed the light quickly but your lions were depleted; I don't know how often that might happen for someone involved in SAR regularly.

    I really like that it uses 3x18650, because this should give you plenty of power for your search. I also really like the distribution of the light--the medium-large hotspot and bright spill area are good for helping you see an entire area in the distance, instead of just a small spot. The durability and solid feel of the S1 are also great for SAR applications.

    As it is, right now if I were to go on a search and rescue op, depending on the environment we'd be in (indoor/outdoor, close/long range), I'd probably take a smaller and lighter torch (single 18650 with good runtime), and have the S1 in my backpack for when long throw and high output is required. As it is, I wouldn't want to have the S1 in my hand all the time, as you can't really just let it hang on a lanyard or hold it in your mouth if you temporarily need both hands free.

    Overall, this is a light that I would take with me for rescue operations, but more as a backup/special use than for primary lighting.

    Long Term Impressions

    I'll fill this part in after carrying the light for a while. If nothing get's added here, either I find nothing else worth noting about the light, or I end up not using it often. I probably won't be able to do much for long term impressions, because the light is only loaned to me for a limited period of time.

    1.27.12 - While doing long-range shots in cold weather (about 20 degrees F), I found that whatever lubrication is used for the control ring thickened up a bit, making it slightly harder to turn. It wasn't much harder, but it was noticeable. However, with cold hands, I found myself wishing again that the ring wasn't angled and the grooves for grip were deeper.
    Last edited by Bigmac_79; 01-28-2012 at 01:49 PM.

  2. #2
    Flashaholic* firelord777's Avatar
    Join Date
    Jul 2010


    Nice review so far

  3. #3

    Default Re: Object/Subject Review: XTAR S1 (3xXM-L U2) - In Progress!

    Thanks firelord!

    I've added some runtime plots, and also a graph of the ramping on the Select mode.

  4. #4

    Default Re: Object/Subject Review: XTAR S1 (3xXM-L U2) - In Progress!

    White wall beam profiles now up!

  5. #5
    Flashaholic* firelord777's Avatar
    Join Date
    Jul 2010


    Nice man, appreciate the work you clearly have put in here, I know how much work these take

  6. #6

    Default Re: Object/Subject Review: XTAR S1 (3xXM-L U2) - In Progress!


    I've added the runtime graph for the Preset Default, the brightness Preset gets set to after loosening and tightening the tail cap, before you use Select. It's not quite the minimum brightness available by using Select, but it's pretty close--it starts at about 5% of High.

  7. #7

    Default Re: Object/Subject Review: XTAR S1 (3xXM-L U2) - In Progress!

    Mode Comparison graph is now posted.

  8. #8
    Flashaholic* firelord777's Avatar
    Join Date
    Jul 2010


    Still watching this thread, thanks man

  9. #9

    Default Re: Object/Subject Review: XTAR S1 (3xXM-L U2) - In Progress!

    New beamshots added, subjective review begun.

    Quote Originally Posted by firelord777 View Post
    Still watching this thread, thanks man

  10. #10

    Default Re: Object/Subject Review: XTAR S1 (3xXM-L U2) - In Progress!

    Objective and Subjective review complete!

    I'd like to add some more long range beam shots if the weather cooperates, so keep an eye on this thread for updates.

  11. #11
    Flashaholic* firelord777's Avatar
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    Jul 2010


    Quote Originally Posted by Bigmac_79 View Post
    Objective and Subjective review complete!

    I'd like to add some more long range beam shots if the weather cooperates, so keep an eye on this thread for updates.
    Sure will

  12. #12

    Default Re: Object/Subject Review: XTAR S1 (3xXM-L U2)

    Some good long-range shots added, along with a "long-term impressions" note.

  13. #13

    Default Re: Object/Subject Review: XTAR S1 (3xXM-L U2)

    XTAR has made some updates to the S1, and the production version is now available. You can see some details on the changes here:

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