The Klarus ST10 is a old name for a newer light from Klarus. The old version was a AA powered light introduced in 2010 that has not been made for many years. This new version is designed with EDC use in mind and uses a 18650 battery, TIR reflector in a compact aluminum body and is USB rechargeable. Thanks to Flashlightz.com for sending this to me to take a closer look at.
Image Gallery: https://imgur.com/a/sXk3F
Video Version of this Review: https://youtu.be/wB-O39IgoZ8
Construction and Stats
This light uses 6061-T6 Aluminum for it’s construction that’s hard anodized black. It’s more of a mat finish! https://i.imgur.com/mi1KcGD.jpg!: https://i.imgur.com/mi1KcGD.jpg . This light is reasonably compact for an 18650 light with built in USB recharging 
. To accomplish this a few design changes have been made. This light doesn’t have a tail cap that’s removable. It’s part of the body tube. They do have 4 reasonably sized lanyard holes. What I really like is they cut a space out for the lanyard to sit flush so that the light can still tail stand with a lanyard 
. The tail cap is not magnetic but there is space where you could epoxy one on the outside if you wanted.
The body tube is square kneraled, 
not super grippy but decent. The threads are large and square cut . It makes it very easy to thread the head on and off. There are fairly stout golden color springs on both sides of the light. On the head there is a spring within a spring 
design that’s unique. The clip is removable and does rotate on the light. It’s pretty stout when trying to remove it. Under normal circumstances it’s not going to come off easily.
The head it’s self is compact. The button is flat and not rubberized. It’s flat and plastic with a small RGB LED in the center 
that’s used as a battery life indicator. It does look to be removable for servicing if you wish. It’s an electronic switch that has a positive detent and does make an audible click. On the opposite of the switch is the USB charging port. It’s covered with a rubberized door that’s attached to the light. The cut out is decently sized 
so it has good compatibility with a wide variety of standard micro USB cables which is a good thing. It also comes with a Klarus branded micro USB cable. More on charging in next section. I measured the overall weight with battery and clip at 108.4g, overall length was 112mm, and width varied between 25-27mm.
LED & UI
This light uses a Cree XM-L2 U2 LED in cool white. No temperature of the tint was given but it’s pretty typical for cool white, not extremely cool. 
The light has a TIR optic 
sitting on top of the LED which produces a hot center with decent spill as you would expect. At close ranges 5” or less you get a hole in the direct center of the beam. This goes away at normal distances. There is then a glass lens with anti reflective coating on top of the optic. Front front bezel is flat and looks removable but I would guess it has some type of lock tight holding it down protecting the lights IPX8 water rating. This light ends up throwing decently for it’s short size. They rate it at 115M throw and in my testing it does that pretty easily.
Output and Runtime
This light has 4 main modes, and no moonlight unfortunately. It’s a feature I like to see on EDC style lights. Low is rated at 10 Lumens for 200 hours. Medium is rated for 100 Lumens for 18 hours, High is 400 Lumens for 4 hours, and Turbo is 1100 lumens for 1.5 hours. 
These numbers were supplied by Klarus, using their 16340 battery. No numbers were given for 18650. This light does have temperature regulation in place and will switch down modes as the light heats up. In my runtime graph 
you can see that actively happening after about 10 minutes, output drops to about 55% relative output and the light cools, and it goes up to about 70% output, and seasawas a few times. As the battery depletes this stops happening after about 25 minutes of runtime. After 100 minutes the light decreases slowly significantly over about 10 minutes to about 10% output where it runs for another 10 minutes and then runs on low for a while longer. I stopped the test at 180 minutes where it was still making light but very little. There is also strobe mode at the full 1100 lumens, and SOS at only 100 lumens.
UI
UI on this Klarus ST10 is simple, The light has memory and will remember any of the constant on modes for quite a while. When it does start out it’s on low. When on you just single click to move up in modes, long press to turn off.
I dislike that it has a double click when on goes to strobe. On most lights this takes you to turbo but not here. Strobe isn’t a feature I use often so it’s a little frustrating to expect turbo and get strobe. When in strobe double click again to enter SOS, single click to exit. The light does offer a lockout mode with the switch. Press and hold 5 seconds to lock, then quick press 3 times to unlock. The light flashes twice to indicate lock or unlock.
USB Charging
This light comes with a branded Klarus 2600mah battery. This is a button top cell with protection. The light will also work with flat tops and unprotected cells as well as charge them thanks to the dual spring design inside the light. I like that the USB charging area is large enough to fit a wide variety of common micro USB cables and that a cable is supplied in the package. When charging the power button up front goes red when charging, and green when it’s completely charged. If you see if flashing something is incompatible or there is a problem.
Up front on the button is the battery charge indicator. During use of the light it will light for 5 seconds and then turn off to show power level. Green is between 70-100, Orange is between 70-30, and red is from 30% to 10. Flashing red is below 10 power remaining and you should charge the light.
Working voltage is 2.5V - 8.4V so it will work with 2 CR123a or 18350 (but it isn’t designed to charge them). I like that the light has options for power, just in case that’s all you have.I measure Parasitic Drain at a stable 7.98mAh which is acceptable.
EDC
As an EDC this is a decent option. It’s not too thick diameter, and the clip is pretty good. I didn’t have problems with it coming on in my pocket without using lockout. I like the clip https://i.imgur.com/JozKq8R.jpg despite it not being super deep carry I typically like. I do wish there was more resistance on controlling it’s rotation. Mode spacing is pretty even no major jumps, I wish it did have a moonlight option and a direct jump to turbo (Double or triple click). USB recharging makes it convenient to recharge most places too.
Packaging
The packaging is a full retail box. 
It’s on the smaller side which is nice. On the outside you have all the important facts such as beam distance, Brightness, water resistant (IPX8) etc. Inside is a plastic try where the light sits. It’s packaged with a lanyard, Klarus branded micro USB cable, and the included 2600mah battery. 
No holster is included with this light.
Pro’s
- I like the little LED under the power button that changes color and acts as a battery level indicator.
- It has a wide working voltage which gives lots of battery options (18350 & 16340) and will recharge any standard 18650.
- 1A charging speed over USB.
- I like they thought to include a cut out in the tail cap to allow the lanyard to pass through and the light still tail stand.
Con’s
- Reusing the name of an old product that’s quite a bit different isn’t the best marketing move by Klarus.
- I dislike the double click to strobe, and would prefer it go to turbo.
- I like that it comes with a battery but I feel like in 2018 the baseline should be 3000mah minimum.
- I wish a warmer LED, or High CRI option was available. I prefer these for EDC use.
- Magnetic tail would be nice
Conclusion
Klarus hasn’t always been my favorite brand, but I like this little light for the most part. I wish the UI was a bit different for an EDC but it’s a trend in the right direction for Klarus. The price point seems to be right too with it being available from FlashlightZ for under $50 for the complete kit. Klarus put some thought into the design of this light to make a good EDC, with features that are popular for the general public looking to get into lithium powered lights at an affordable price range. As an enthusiast there are a few things I would change but I can live without them too. Check out the link in the description below to see more about this light and where you can pick it up on FlashlightZ website or Amazon.