Klarus FlatTac X1

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Klarus FlatTac X1 Specifications & measurements

Brand & Model	Klarus FlatTac X1
Flashlight category	EDC, Flat Light, Tactical
Battery config.	Built-in
Switch type	Dual rear
Dimensions:
Length	148 mm
Head diameter	15 mm
Weight with battery	124 g
LED & Beam
LED type	Unknown
High CRI	No
Focusable beam	No
Features
Onboard charging	USB-C
Power bank	No
Specifications and measurements
Specified output	4,200 lm
Measured output (30sec)	118 lm
Max. measured output	3,445 lm
Specified beam distance	230 m
Measured beam distance (30sec)	191 m
Specified beam intensity	10,800 cd
Measured beam intensity (30sec)	9,081 cd
Overall rating	4.5 stars
Review publication date	September 2025

Klarus prides themselves on tactical dual-switch flashlights and now offers a flat tactical dual-switch line, aptly called the FlatTac. This particular light is the X1 model, which has two variations: The X1K, which has a tactical ring on the side, and the X1E, which is plain. Besides the ring, they’re both the same. This review covers both at once! Two for one, just like Klarus’ tactical switches! Let’s take a look at the X1!

What’s in the package

The FlatTac X1 comes in a two piece, full color, cardboard box with glossy photos of the light. Upon lifting the top half off, you’ll be presented with a quick start card on top of the light itself, held firmly in place by a molded plastic insert. There’s another compartment in the plastic insert for the USB-A to USB-C cable, while the full instruction booklet is underneath.

The full contents of the package include:

• Klarus FlatTac X1
• USB-A to USB-C cable
• Quick Start card
• Instruction manual

The FlatTac X1 is Klarus’ first flat light! The extra-thin aluminum unibody and steel bezel are advertised to be protected by 40μm thick anodization, which I believe should fall under HAIII spec. It comes in two versions: X1K, which has a tactical ring, and X1E, which does not have the ring.

Otherwise they’re identical. Think hard before choosing as there’s no adding a ring after the fact; it’s screwed into the body, and there are no screw holes on the X1E. The tactical ring has a ceramic glass breaking bead at the top, though I’m not testing it out. This is just speculation, but the ring appears to be aluminum.

I don’t test glass breaking claims to begin with, but I’d predict that if you tried punching out a window with the ring’s bead, the thin aluminum structure of the ring would likely just crumple under the force and pin your finger to the light. It’s big enough to hold with a gloved finger, though.

I do think the ring helps with drawing the FlatTac X1 out of your pocket more quickly. The downside is that the ring is right at the level of the clip, so it may force you to clip it to the pocket further towards the middle than you would otherwise, depending on where you clip it (left front pants pocket, for example).

Additionally the clip, on either model, leaves about 3cm (more than an inch) sticking up out of your pocket. If you prefer a deep carry, you won’t be getting it with this light. Part of it may have to do with the fact that it’s almost 6 inches long, and that’s a bit on the long side for pocket carry. If I don’t clip it to the edge, it will still stick out at the shallowest part of my pocket.

Regardless of where it sits in your pocket, one thing is for sure: This light is flat. While there may be other flat lights which manage to squeeze the front part of the body below the FlatTac X1’s height of just under 15mm, they bulk up towards the tail end. The FlatTac X1, however, is 14.8mm thick from tip to tail. I have pens thicker than that! My wallet is thicker than that! Lengthy, yes, but the FlatTac X1 is definitely not bulky.

Using the FlatTac X1 is easy. The extra length outside of your pocket allows you to grab and pull if you don’t have the X1K version with the ring, and lends itself perfectly to the overhand grip, with a 10-degree slant to the tail cap, allowing your thumb to naturally line up perfectly with the buttons.

If you carry it on your right side, that is. When in your left pocket, the 10-degree slant is opposite and while it can still be used, it’s harder to line up your thumb with both buttons. I put emphasis on in, because if you carry it on the outside of your left pocket, it’s just as easy to use if it’s on the inside of your right pocket.

But how often do you carry a light on the outside of your pocket? It’s definitely designed for right-hand use. What they should’ve done (or do for the potential next generation) is have screw holes for the clip on both sides of the light so you can reverse it. But then that would get in the way of the screen…

Oh yeah, the FlatTac X1 has a screen! This little display can show you how much battery is left, the output level you’re on (and its spec lumens), a countdown from 15 for turbo, the company name of course, and whether the light is overheating (HOT!) or the proximity sensor is activated (NEAR!).

The FlatTac X1 only has an IPX6 rating, likely due to the USB-C charging port. The rubber cover isn’t terribly snug, so I wouldn’t test this underwater. But you have to have onboard charging if you have a built-in battery, and that’s a standard downside, unless you have a very tight cover.

Likewise, since you can’t unscrew a tailcap to lock it out, it has electronic lockout. Three clicks of the aux button and you won’t have to worry about accidental activation. What’s nice is that you can still use momentary “moonlight” while it’s locked out.

I put that in quotes, because what they call moonlight is actually 15 lumens. That’s more of an extra-low level to me. True moonlight is generally around 1 lumen. Momentary moonlight is also available while not locked out by holding down the main button.

A click of the main button will turn the light on. Holding the aux button down will give you all 15 seconds of momentary turbo, while a click will give you instant strobe. Plenty of options available via a single click or hold from off!

The FlatTac X1 is covered by a 2 year warranty against defects if purchased through their website. I assume if it’s purchased elsewhere, you have to go through that reseller for any warranty support.

Klarus doesn’t provide information on the emitter they used for the FlatTac X1, but you can see them through the clear TIR optics. Based on the fact that they’re quad-core and the placement of the bond wires, it looks to me like it’s powered by a pair of Luminus SST-70s. These are 5050 (5.0mm²), domed, quad-core, 6V/12V emitters which could easily reach the specified 4200 lumen output on turbo. 

On the lower levels, the wide hotspot has a noticeably green tint but by the time you get to medium high, it gets more neutral, but the DUV is still pretty high. Both the hotspot and spill have vague edges and though it’s a dual emitter setup, the output is very circular rather than oval unless you’re very close to your target.

Speaking of getting too close, the FlatTac X1 has a proximity sensor which will drop the output to 200 lumens (medium) when the light is a few inches or so from an object and above that level. The display also reads, “NEAR!” When you move it away, the output will go back to the previous level. While this can help avoid pocket fires, it’s a divisive feature especially because it cannot be disabled. You can see the hole for the sensor between the two emitters.

I got inconsistent results when playing around with the sensor. It seems to activate at around 3 inches (8cm), but doesn’t always, depending on the color of the surface it’s pointed at. In fact, sometimes it only briefly dimmed the output, but then it went right back to the normal level even on turbo. Since lockout is a mere triple-click away, I’m not sure I’d rely on the sensor to prevent damage to my pocket or bag. At least dimming can’t be accidentally activated from a distance.

I don’t believe there’s a glass lens, leaving the TIR exposed. Maybe that’s a good thing, since if you decide to use the four ceramic bearings embedded in the stainless steel strike bezel to try to break glass, you won’t have to worry about breaking the lens, too. It’s possible that the TIR could get scratched though, given that it’s plastic.

More details: 

• LED Type: Unknown
• High CRI: No
• Focusable beam: No

Spectral measurements: 

I used an Opple Light Master Pro to measure the flashlight at 1 meters distance. 

Mode:	CCT:	CRI Ra:	duv
Turbo	5722 K	67.5	0.0078
Moonlight	5172 K	61.9	0.0114

Dimensions:

Klarus FlatTac X1	Millimeters	Inches
Length	148 mm	5.8 in
Head diameter	15 mm	0.6 in
Body width	32 mm	1.6 in
Width at ring	65 mm	2.5 in

Dimensions are rounded to the nearest millimeter and the nearest tenth of an Inch.

Weight:

Klarus FlatTac X1	Weight in grams	Weight in oz
X1K (with ring)	124 g	4.4 oz
X1E (no ring)	119 g	4.2 oz

Weight is rounded to the nearest gram and tenth of an Oz.

Flashlight size comparison with its competition:

Group 1: Emisar D4V2, Klarus FlatTac X1K, Convoy S2+

Group 2: Wurkkos HD01 Pro, Klarus FlatTac X1K, Olight Arkfeld Ultra

Available modes: 

• Moonlight, Low, Medium, Medium High, High, Turbo

Available blinky modes:

• Strobe, SOS, Beacon

From OFF:

Main switch:

• Press and hold: Momentary moonlight
• Single click: On to memorized level

Aux switch:

• Press and hold: Momentary turbo
• 1 click: Strobe
• Double click: SOS
  • Double click: Beacon
• 3 fast clicks: Lockout

From ON:

Main switch:

• Press and hold: Off
• 1 click: Cycle levels

Aux switch:

• Press and hold: Momentary turbo
• 1 click: Strobe
• Double click: SOS
  • Double click: Beacon
• 3 fast clicks: Lockout

Mode memory:

• The last used non-turbo level is memorized.
• If you use momentary moonlight, it will become the memorized level.

Shortcuts:

• To Moonlight: Hold main switch from off
• To Turbo: Hold aux switch from any level/mode
• To Strobe: Single-click aux switch from any level/mode

Strobe/blinkies

• Strobe: Single-click aux switch from any level/mode
• SOS: Double-click aux switch from any level/mode
• Beacon: Double-click aux switch from SOS
  • 1 flash every 3 seconds
• Single click to exit any of these modes.

Lock-out feature: 

• Triple-click the aux switch from any level/mode to lock the light. This turns it off if it’s on.

Unscrew to Lock-out:

• N/A

PWM

• While the FlatTac X1 does not use pulse-width modulation as Klarus advertises, all levels do seem to have some amount of “sawtoothing.”

Additional/summary info on the UI: 

• A fairly straightforward UI. The red aux switch basically takes precedence over the main switch.

As with any flat light, the built-in battery limits the testing we can do with it. Klarus claims a 2150mAh capacity for the lithium polymer battery in the FlatTac X1 and I’d be inclined to agree. My USB power meter read around 2300mAH of electricity was used to fully charge the light (not all of that makes it to the battery due to the fact that nothing is 100% efficient). Klarus also states that low voltage protection engages at 3V, and the built-in USB-C charging stops at 4.2V. We’ll just have to take their word for it.

I used my 65W charger and observed 5.2V and 2.0A used, for about 10.3W. In testing, it only took about an hour and 40 minutes to fully charge the light, which is lower than the 2 hours Klarus said it would.

Batteries	Details
Compatible batteries	Built-in lithium polymer
Incompatible batteries	N/A
Low voltage protection/warning	Output decreases
Onboard Charging:
Onboard charging	USB-C
Power bank functionality	No
USB-C to USB-C charging	Yes
Max power of USB charger (port)	65 watts
Max power measured	5.2V, 2.0A, 10.63W
Final battery voltage (charged)	4.2V (claimed)
Avg. onboard charge time	1h 40min

Lumen measurements

How Lumens are Measured: Understanding ANSI FL1 Standards How Lumens are Measured: Understanding ANSI FL1 Standards: The ANSI FL1 standards specify that output in lumens should be measured 30 seconds after turning on, as this is the standardized time for measuring brightness according to the industry standard. This is why we focus on this part in our measurements. The ANSI FL1 standards require an ambient temperature of 22 ± 3°C. We record the ambient the ambient temperature to identify potential reasons for any observed discrepancies.

To obtain these numbers, I used an integrating sphere and Extech SDL400 data logging lux meter. Measurements have been calibrated using a standardized calibration light provided by 1Lumen.

Overall, the X1 does miss its specs, but it still has some powerful initial output. Turbo hits 3445 lumens at turn on, high is 1641 after 30 seconds, and medium-high is 1163. Even after 10 minutes, high is still almost 750 lumens

Note that turbo is specifically timed for 15 seconds, that’s why it shows 118 lumens after 30 seconds. It’s also thermally limited, so if you try to go right back to turbo, you might only get a few seconds before it drops back down.

I did have to run these tests twice, because I realized after the first batch that the proximity sensor was causing it to dim repeatedly, messing with the numbers. To combat that, I cut a thin strip of electrical tape and placed it over the sensor, and it prevented it from activating which allowed me to get clean data.

Mode	Specified output	Turn on	30 sec.	10 min.
Moonlight	15 lm	14 lm	14 lm	14 lm
Low	65 lm	45 lm	45 lm	45 lm
Medium	200 lm	91 lm	91 lm	91 lm
Medium-High	1200 lm	1197 lm	1163 lm	131 lm
High	2200 lm	1709 lm	1641 lm	746 lm
Turbo	4200 lm	3445 lm	118 lm	–

*Turn-on and 30 second measurements are done manually, while the 10-minutes readings comes from the runtime graph. This is our standard approach, though some reviewers may choose a different approach.

Ambient temperature during testing:

• 27°C/80°F

Parasitic drain:

• Unable to measure due to the fact that it’s sealed.

Battery Life: Runtime graphs

How Runtimes are Measured: Understanding ANSI FL1 Standards About ANSI FL1 runtime standards: The runtime is measured until the light drops to 10% of its initial output (30 seconds after turning on). This does not mean that the flashlight is not usable anymore. The last column shows how long the light actually works till it shuts off. If there is a + symbol, it means that the test was stopped at that particular point, but the light was actually still running. This happens on certain occasions, with certain drivers, firmware, or batteries.

To obtain these numbers, I used an integrated sphere and Extech SDL400 data logging lux meter. Measurements have been calibrated using a standardized calibration light provided by 1Lumen.

I like to do a full runtime, but I’ll skip levels like moonlight which are designed to last 24 or more hours, so it was a surprise to me when high was still running the morning after I started it, when I got home from work that day, the next morning, and when I got home from work the next day, and all the way to that evening! Granted, it spent most of that runtime at 6 lumens, but wow. Medium-high acted the same way, so I assumed medium and low would as well, but they were both constant until their abrupt cut offs.

Since high starts off so, well, high, it does actually reach 10% after only 16 minutes. In fact, if you look at the graphs, high and medium high both level out around 140 lumens after very brief stints above 1000, while turbo drops directly that same level. With medium also being about 100 lumens, the FlatTac X1 is really only a 100 lumen light with extended use.

On a positive note, look at how well regulated the output is! Not only is the output perfectly flat, the stepdowns are also perfectly straight!

Again, turbo is timed to 15 seconds.

Mode	Specified runtime	Runtime (ANSI FL1)	Time till shut off*
Moonlight	48h	–	–
Low	15h	21h 55min	21h 55min
Medium	6h	10h 06min	10h 06min
Medium-High	5h 40min	4h 10min	38h 33min
High	5h	16min	49h 18min
Turbo	15s	15s	–

*The last column reflects the total runtime until the light turns off. A “+” symbol indicates that the test was stopped at that point, but the light continued to run. This typically occurs with certain drivers, firmware, or battery types.

Peak beam intensity and beam distance measurements

About Peak beam intensity: Understanding ANSI FL1 Standards About peak beam intensity The calculated value of distance in meters at which the flashlight produces a light intensity of 0.25 lux. (0.25 lux is about the brightness of a full moon shining on an object). This means that the intensity has decreased so much, it becomes difficult to see darker objects, or objects that don’t reflect light. The columns ‘Meters’ and ‘Yards’ use rounded numbers.

The numbers for candela were obtained with an Extech SDL400 data logging lux meter at 1, 5, and 15 meters, then averaged.

The most notable difference from spec here is medium, which wasn’t too much higher than low, but in the output test, you can see that medium was significantly lower than was specified there, too. Turbo almost reaches what was specified at turn on, but high is only about half the candela it should be at 30 seconds. As above, keep in mind that this is peak, and it will only sustain ~400 cd past 15 minutes or so.

Mode	Specified intensity	Specified beam distance	Candela measured	Meters	Yards
Moonlight	60 cd	30 m	65 cd	16 m	18 yd
Low	584 cd	42 m	144 cd	24 m	26 yd
Medium	2724 cd	104 m	338 cd	37 m	40 yd
Medium-High	5124 cd	143 m	3112 cd	112 m	122 yd
High	9360 cd	185 m	4900 cd	140 m	153 yd
Turbo	10800 cd	230 m	9081 cd	191 m	208 yd

Ambient temperature during testing:

• 24°C/76°F

Camera settings and distance: These were taken with a Canon EOS 600D with the following settings: 

• WB 5700K, ISO 1600, Speed 0.5sec, f/4.5, 18mm
• Distance to the other end of the playing field is 100 meters.

Beamshots of the following flashlights compared:

• Klarus FlatTac X1
• Olight Arkfeld Ultra
• Wurkkos HD01 Pro

Please note that the following beamshots are mainly intended to showcase the beam pattern and beam quality, rather than overall performance. These images are typically taken directly after activation, and in different seasons or weather conditions, and therefore do not fully represent its overall performance. In few cases the camera settings are even different and therefore not meant for performance comparisons. For accurate performance metrics, such as output, beam distance, and runtimes, you need to look at the performance section of this review.

Disclaimer: This flashlight was sent to us for review at no cost by Klarus. We have not been paid to review, nor have we been holding back on problems or defects.

Buy your Klarus FlatTac X1 here

1lumen selects and reviews products personally. We may earn affiliate commissions through our links, which help support our testing.