Nitecore T4K Review “The Worlds Brightest Keychain Flashlight” (4000 Lumens, USB-C, 4 Emitters)

Today I have Nitecore’s new T4K the worlds smallest 4000 lumen light. This continues on Nitecore’s trend of coming out with increasingly larger, higher performance keychain style lights, with the TIP, TUP and now the T4K. Thanks to Nitecore for sending this to me to look at and review. I will have a link to where you can find it if you are interested. 


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Packaging & Accessories

Packaging here is really stepped up, and it reminds me of Olight boxes with its magnetic closure and Thank you Message inside the front lip. The sides have some info and feature list on the back. Inside you get the T4k itself, a USB-A to C cable, a keychain clip, the manual and a warning about using lockout (Smart). 



The Nitecore T4K will look similar if you are a TUP owner, and it has a similar physical layout with a few changes. It’s made of a black anodized aluminum construction shell that’s held together with torx bits smaller than T4. On the top you have 2 buttons, a power and mode, as well as a small OLED screen that helps navigate the UI. It’s not necessary but I really like it. Branding is minimal which is nice as well.


On the front you have what looks to be a custom optic and flat face, when the light is on at the front you get kind of a side indicator like on a car at the seam which is kind of neat. At the back you have the USB-C port with no cover, and the mounting point. Nitecore says it can withstand 66 pounds of weight which hopefully is significantly more then you have on your car keys, but that should help it from getting caught too if pulled. This has a quick detach point too thats quite solid, and made of metal. I will talk more about the clip in the retention section.


Size & Weight

I measured the length at 36.34mm width at 29mm, and thickness at the head at 25.2mm. Weight with the clip and quick detach is 76.3g. The T4K is IPX 54 rated which means splashing water and dust should be fine. 


This compares to the TUP which comes in at 53.9g and is smaller in all dimensions. If you are TUP owner and are happy with the size the T4K isn’t that much bigger but is larger in all dimensions. Here is a photo of a few other keychain lights that I have and you can see the T4K just towers over all of them. It’s even a little larger then the Olight S1R II Baton. 



The T4K has a few options for retention. First you have the pocket clip on the back. It’s a wide clip, that’s attached via small Philips screws which seem like an odd choice given the rest of the light is assembled with Torx. This clip allows the light to sit pretty low in the pocket, if you choose to carry it that way. I won’t due to it’s diameter but it also clips on to molle webbing pretty well. 


At the back there is a quick release mount to attach it to the included key ring or you could use a small diameter lanyard too. It has a spring mounted button to attach and detach and can withstand a pull force of 66lbs which is impressive.


LED & Beam

The T4K has 4x Cree XP-L2 V6 in Cool White, no exact tint is specified but it’s pretty standard cool white, not super blue. The beam pattern out of the optic is fairly round but far from perfect, it has a few artifacts but it’s only really noticeable on a wall or flat surface and not in use. It’s a large spot, with very minimal spill, a little surprising as I expected this to be mostly flood. Rather then tell you all of the official technical data, here is the slide from Nitecore. 


Heat and Runtime 

Turbo runtime is going to be easier if I show it here due to the sample rate of my light meter, so let’s do that. Remember that this is 4000 lumens and a very small light. At first it will run for 10 seconds, before stepping down, I can keep running retriggering turbo and you will see the graph on the screen get shorter and shorter as the light heats up. After doing this 6 times the light does warm up. The thermocouple on the side during my testing said 52C (126F) but it doesn’t feel too hot to hold in the hand. With the normal modes it only gets slightly warm. After these 6 turbo runs the battery voltage did drop from 4.2V to 4V. I do wish I had a thermal camera because of how this one spreads heat out on the bottom of the light and through the clip. Not your typical flashlight. 


Normal mode runtimes were pretty good, they have flat outputs until they run out of power, with a small spike at the end. I tested High and came up a little short of Nitecores official rating of 2:45:00, at 2:17:00. So you might take the other runtimes with a small grain of salt.



This light ships with 2 UI, the default being “Demo” mode. Given the package is a sealed box without a window, I can’t think of a legit reason why the light has a demo mode, and why it would be the default. Nitecore says this is for EDC use, but I would prefer to manually turn the light off, if my task takes longer than 30 seconds. For practical use the user needs to switch it into daily mode by pressing both buttons at the same time while the light is off.


Daily mode is more straightforward and what you would expect. The light starts in moon light mode and linearly goes up. Ultralow mode is 1 lumen, then 15 lumens, 65 lumens, 200 lumens, and momentary turbo of 4000 lumens. This is the same as the Nitecore TUP except for the difference in Turbo output. The light has memory in this mode and will remember where you were last at. It has 2 buttons, basically a power and a mode button.

The light has direct access to low and Turbo. To access low, when the light is off (and not locked) press and hold the power button to access 1 lumen mode. To access tubo press and hold the mode button, and this is in momentary.


The light also has 2 lockout modes. Lock 1 is half lockout mode. It locks the power button but if you press and hold (about 1 second) the mode button you get access to turbo. To exit lockout you have to hold both buttons at the same time. In lockout mode 2 the light won’t turn on until unlocked. 



Internally the Nitecore T4K has a 1000mAh lithium polymer battery. For recharging the light has a USB-C port on the rear. The interesting thing here is that it doesn’t have a cover to prevent dirt and water. I think it would be nice if it did but I suppose it’s fine that it doesn’t. We all carry around smartphones most with exposed ports and things end up being fine. 


Total charge time of the internal battery was 1:20:00, with max charge rate bing 1.1V at the 32 minute mark. The light does support charging via USB-C to C cable and via a USB-C PD charger which is the way it should be. It’s nice the display say the voltage of the battery as well. 



  • Nice to see USB-C being used here and full compatibility but a port cover would be nice
  • I like the screen, and it gives a lot of useful info like output, estimated runtime, and battery voltage.
  • UI makes sense here, just remember to use lockout if it’s being carried to prevent an accidental blast of 4000 lumens.



  • Too big for the keychain name, it’s more of a jacket pocket light
  • Short turbo runtime but that’s to be expect at this size
  • Pricey if you think of it as a keychain light, not terrible if you think of it more as a pocket light.



My conclusion on the Nitecore T4K is it produces a ton of light from such a small package, but I don’t think it should be called a keychain light. It’s just just quite a bit larger than I want on my actual keychain especially if I try to put them in my pants pockets. I think it works better as a something to put in a jacket pocket. Runtimes on the lower modes are long enough that you could realistically go walk the dog with this one more then likely if you wanted, and the UI is such that it’s easy to boost from 200 lumens to 4000 lumens if you need more light. That mode spacing gap though is huge between 200 and 4000 lumens, A mode of 1000 or 1500 would be nice to bridge the gap especially if you could get a minute or two out of it. 

I don’t always talk about price but I feel like I kind of have to here, the current MSRP of the T4K is around $80 at the time of this review, and I feel like that’s on the pricey side for what’s targeted to a keychain light. It’s got the output, screen, and USB-C but that’s just a lot. 


The TUP might be more practical but the T4K is the output king. If you want something to impress someone with how bright it can be for how small it is the T4K does a great job of that and I can recommend it.