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ReviewTheLight: Nitecore P20UV (800 White Lumens + 320mw of 365nm Ultraviolet)

2 September 2014
Trustfire Taschenlampen Hypnose Hannover
Nitecore is one of the leading innovators in flashlight tech, consistently among the first to adopt new ideas and designs. In the P20UV, Nitecore adds a white/UV light combo to their dual rear power/mode switches and uses three different interface options to create a very versatile light.

Thanks to Nitecore for providing the P20UV for review.

I’ll be reviewing the P20UV 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). 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.

Video Review

Below is a video review of the P20UV. Due to my old image hosting site closing down, I've got new restrictions on image uploads and have replaced the "Construction" section of my reviews with a more detailed video review.

This video is available in 1080p HD, but defaults to a lower quality. To select the playback quality click the settings button (looks like a gear) after you've started the video.


Manufacturer's Specifications

Price: 75 USD

Product Manual


Plus, here's a few shots with some good detail - Click for full size.

User Interface

The P20UV has a three choices of interfaces, with the two rear buttons controlling the output of the single white and four UV emitters. The Power switch is raised higher of the two and is covered with a rubber boot, and the Mode switch is activated by a metal lever system with a low wide pressing area. The modes are Low -> Medium -> High -> UV, but not all modes are available on all interfaces.

To select which of the three interfaces to use: Turn the light off, loosen the head, press and hold the Mode button, re-tighten the head. The light will then flash 1, 2 or 3 times, indicating which interface has been selected. Interface 3 is the default.

The three interfaces of the P20UV are:
1) Tactical: High -> UV
2) Law Enforcement: Medium -> High -> UV
3) General: Low -> Medium -> High -> UV

So, of the four modes available, General has all of them, Law Enforcement has three of them, and Tactical has two of them.

To turn the light on, you can either hold the Power switch about halfway down, and the light will turn on until you release pressure, or you can click it all the way down, and it will stay on until you click it again. Once the light lis on, you cycle through the available modes (determined by which of the three interfaces you selected) by quickly pressing the Mode switch.

The P20UV also has Nitcore's "Strobe Ready" feature. At any time the Strobe mode is easily accessible: if the light is of, the Strobe mode is activated (momentary on) instantly upon pressing the Mode switch, and will stay on until you release the mode switch. If the light is on, the Strobe mode is activated (constant on) by holding the Mode switch for about half a second, and will stay on until you press the Mode switch again or turn the light off with the Power switch.

Finally, the battery status can be roughly checked by loosening then tightening the tail cap by flashes of a red LED under the power switch. Three flashes indicates a battery charge of >50%, two flashes means <50%, and one flash means the battery is almost dead.

Action Shots

You can click on any of these shots to see them full size.

Light in Hand



White Wall
ISO 100, f/3.5, 1/20"

*the UV photo was taken as a closer distance and on a white piece of printing paper, instead of the normal wall I use, because the walls of my house do not fluoresce ;)

Indoor Shots
ISO 100, f/3.5, 1"

Outdoor Shots

ISO 100, f/3.5, 2.5"


Submersion: I submersed the P20UV under a foot of water for about an hour, clicking both switches several times. I found no evidence of water entering or damaging the light.

Heat: The P20UV automatically steps down in output after a few minutes for both High and Medium mode, so there is no chance of overheating unless you repeated re-activate the High mode after stepdown many times.

PWM: The P20UV does use pulse-width modulation on Low and Medium modes, but not on High mode. It is not noticeable to the naked eye, but is detectable by a camera.

Drop: I dropped the P20UV from about a meter onto various surfaces (including grass, carpet, dirt, and hard wood), and found no cosmetic or functional damage.

Reverse Polarity Protection: The P20UV does have built-in reverse polarity protection of a partially mechanical nature, so you will need to use button-top cells in this light.

Over-Discharge Protection: The P20UV automatically steps down in brightness after three minutes, then steadily decreases in output for the rest of the run, so a dim light is your signal to change the battery. Also, you can use the built-in battery voltage indicator to check the battery status at any time (see the UI section).

Spectral Analysis

All light that we see as white is actually made up of several different colors put together. The relative intensities of the different colors in the mix are what determine the tint of the white we see. For example, cool white LED's have a lot of blue, and warm white LED's have more red or yellow. This measurement was done on a home made spectrometer. The plot below the picture is corrected for the spectral sensitivity of the human eye. Note: the peak in the 900nm region doesn't really exist, it's a piece of the second-order spectrum that's showing up here because of the high intensity of the light source.

This spectrum of the UV LED's is particularly interesting, and is at the border's of my instrument's detection range. If you look closely you can also see a bit of light in visible range (the red and green band, corresponding to the two bumps near 550 and 600 nm), caused by the slight fluorescence of the plastic in my spectrometer's diffraction grating ;). As with the white spectrum, there is a second-order spectrum that gives a false reading at longer wavelengths (the right side of the graph), and this can be ignored.

Output and Runtime

ANSI FL-1 runtime ratings are the time it takes for a light to fall to 10% of it's original output (counting from 30 seconds after turning the light on).

The vertical axis of the graphs below 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:seconds. These graphs may be truncated to show detail.

Mode Comparison



It's a bit hard to see what's going on in these pictures, but it matches what's explained in the manual. For both High and Medium mode, there is a forced decrease in output after about 3 minutes (to decrease heat and increase battery life), after which the output is unregulated. However, if you desire you can turn the light back to High or Medium output after the drop, you just need to be aware of the heat.

Throwing Distance

ANSI FL-1 standard for stating a light's throwing distance is the distance at which the peak beam intensity (usually at the center of the beam) is 0.25 lux. I calculate throwing distance and candela (lux at 1 meter) by measuring peak beam intensity at five different distances and using the formula lux*distance^2=constant.

Subjective Review

Quick break down:

+ Bright
+ Surprisingly nice beam
+ Has 365 nm Ultraviolet
+ Different mode sets available
+ Simple UI once you set it
+ "Strobe Ready"
+ Hinge switch is great
+ Little visible light from UV emitters
+ Fun to use

- Not as much UV as their CU6
- UI takes some reading to figure out
- No regulation after 3 minutes

So, I'll start of by saying this light has been a lot of fun to use, but that's not the point of the P20UV. This is my first professional-style ultraviolet light, and it's just that--very professional. The whole setup of the light shows that it's not built to be played with, but instead is for those who need ultraviolet light on a regular basis, and will benefit from having white and ultraviolet light together in the same device.

First, the user interface. It's a bit complicated to work out at first (watch the video above to see me fumbling through it ;) ), but once you get it set up it's very simple, and the multiple interface options means you'll be able to customize it for your purposes. Personally, I like the "General" interface, which has all output levels available, but I can certainly imagine someone preferring "Tactical" setting, which has only the UV and High (plus Strobe). It is a bit difficult to do the sequence required to change which interface you use, but it's not the sort of thing you're likely to be doing in a high pressure situation, rather you will want to choose the setting you like in advance, then use it when your work begins and not plan on changing it during use. Once you have it set, the Power button will always turn it on/off, and the Mode button will easily change you between the modes. I love the use of the hinge-style switch, and I'd like to see it implemented in a lot more lights (thought no doubt Nitecore intends to keep it to themselves, and I suppose that's probably fair :sigh:). It's very easy to use, and I appreciate that the power switch extends further but the mode switch is wide and hard metal, so they can be easily distinguished. Having the switches right next to each other but easily distinguishable means you only need one grip to access both switches, but you're not going to get them mixed up. In addition, it's nice to have the Strobe readily available but not part of the main mode sequence. I've said hundreds of times, if a light is going to have a strobe mode it needs to be easy to access on purpose and very hard to activate by accident. The only thing that I don't like about the Strobe on the P20UV is that the time it takes to activate when the light is already on seems a little bit short, so that if I only want to change the mode I have to remember to press the button and release quickly. It wasn't a huge issue, just something I had to get used to. When the light is off, I do like that the Strobe activates instantly.

Another thing to note is that the UV mode is present in every setting, so as I said, this is a light for those that are going to need UV on a regular basis. It also does get remembered by the mode memory, so you can set it to be the first thing that happens when you turn the light on. I also really like that the UV is in the 365nm region (as confirmed by my measurements). From what I've seen, 395nm is a more popular choice for many lights. That's fine, but you need to be aware of the best wavelength to use for your desired application, as different materials fluoresce best at different wavelengths. So, if you need 365nm for your application, it can be harder to find a good light for it. Generally, 395nm is on the border of visible, and is probably what most people think of when they envision UV light, as it has that distinctive deep purple look, so if you don't mind that extra visible light then 395nm can work well. However, if you really need fluorescent materials to be quickly distinguishable from their surroundings, that visible light can get in the way. 365nm UV is further out of the visible range, so even the trailing end of the peak is unlikely to be visible, and fluorescent objects will be the only things lit by the light, making them much easier to pick out from their surroundings quickly. The first things that come to mind are looking for UV authentication marks on currency or looking for scorpions, and in both of these cases you want to be able to identify the material quickly. Unfortunately, I've heard many reports of 365nm UV LED's that put out a lot of white visible light in addition to their UV light. I can't find any explanation for this, but my guess is that the material of the lens or of the LED dome itself are fluorescing, giving off the white visible light. This can be a hindrance in those situations where you want little other light to distract you. Fortunately, the P20UV seems to put out very little visible light, though the emitters do have a faint white/purplish look to them [I don't recommend looking at them long, I do recommend reading up on UV eye safety]. You can see the beamshots and the spectrum graph above to see how little visible light is put out. So, the P20UV is going to be good for those cases where you're looking for materials that fluoresce well at 365nm, and you want little visible light from the surroundings.

On the negatives, this light doesn't have as much sheer output as some other UV lights, such as Nitecore's CU6. I don't have a way to measure wattage, but they claim the CU6 has 3000mW, and the P20UV has 320mW. This is believable to me, because the CU6 uses a larger more modern LED for it's UV emitter, and the P20UV uses a set of four lower-output 5mm LEDs. In addition to this, the P20UV emitters don't really get prime position in the reflector, compared to the single large emitter that it's mostly it's own reflector in the CU6, so the P20UV has a much floodier UV beam, which means you'll be using at closer ranges. If you need more UV output and better throw, the CU6 might be worth a look.

The only other negative I found is that after 3 minutes the P20UV drops it's regulation and goes to a lower output. This isn't a huge issue, as if you want you can turn it off and back on to get back to the high output, but it's just not ideal if you want to be picky. It will help keep you from overheating the light or needlessly draining the batteries though, so you decide for yourself if you like that feature.

When it comes to the little things, I have come to expect Nitecore to nail them, and they have with this light. The construction is solid, the threads are smooth, the switches are good quality, the style just looks good, the beam even manages to look pretty good with the four holes in the reflector. These all come together to make the light enjoyable to use.

In conclusion, the P20UV is a rare light that combines high output white with high energy UV in a very professional manner, giving several options of UI's for various circumstances. If you need UV on a regular basis and plan to use it mostly at close range (I find things within ~20 ft easy to see), the P20UV is going to be among your best options.

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.
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29 April 2011
der Ottostadt an der Elbe
Hey Bigmac, welcome to TLF! :thumbsup:

It's nice to see you here. :)

Thanks a lot for this huge and informative review!

I like the P20 for its hinge switch and it's great to see there is a UV Version available for the enthusiasts. :)


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