Warning: pic heavy, as usual.
The SRT7 (aka "Revenger" ) from Nitecore is the first member of a new "Smart Ring Tactical" SRT series. As the title implies, these lights will use a magnetic control ring – with a continuously-variable output ramp feature.
The SRT7 is a 1x18650, 2xCR123A/RCR model that is distinguished by several additional features, including multi-color secondary LEDs. I believe it is also the first Nitecore light I've tested with the latest XM-L2 white LED. Let's see how it compares to the competition …
Manufacturer Reported Specifications:
(note: as always, these are simply what the manufacturer provides – scroll down to see my actual testing results).
- Utilizes the latest CREE XM-L (XM-L2 T6) LED for a maximum output of up to 960 lumens
- Infinite brightness adjustment from 0 to 960 lumens
- Boasts a peak beam intensity of 23,256cd and a throw distance of up to 308 meters (ANSI FL1)
- High efficiency circuit board provides up to 200 hours runtime on lowest output level
- Equipped with unique multi-colored (red, green and blue) tactical / signaling lights
- Six rapidly switchable functions to select from
- Multi-functional power indicator light displays low battery status
- Patented spring-loaded impact absorption mechanism with reverse polarity protection
- Stainless steel titanium-plated two-way clip
- Stainless steel retaining ring protects core components from damage
- Toughened ultra-clear mineral glass with anti-reflective coating
- Constructed from aero grade aluminum alloy
- Robust HAIII military grade hard-anodized
- Waterproof in accordance with IPX-8 (two meters submersible)
- Impact resistant to 1.5 meters
- Tail stand capability
- Purpose-designed for law enforcement, hunting and tactical applications.
- The world’s first line of flashlights to feature third generation SSR (smart selector ring) technology
- Smoothly and rapidly select brightness levels and function by rotating a smart selector ring
- Second generation of ‘Crystal Coating Technology’ along with ‘Precision Digital Optics Technology’ provide extreme reflector performance
- Dimensions: Length: 158mm, Head diameter: 40 mm, Tube diameter: 25.4mm
- Weight: 173g (without battery)
- Accessories: Quality holster, removable clip, tactical ring, lanyard, spare tail cap button and spare O-ring
- MSRP: ~$110
The SRT7 comes in standard Nitecore retail packaging. Inside, you will find the light, holster, wrist strap, hard plastic grip ring, extra o-rings and tail boot cover, pocket clip, manual and warranty card.
From left to right: AW Protected 18650; Nitecore SRT7, P25, MH25; Eagletac G25C2-II; Sunwayman T21CS; Armytek Predator Pro v2.5.
All dimensions directly measured, and given with no batteries installed:
Nitecore SRT7: Weight: 172.4g, Length: 158mm, Width (bezel): 40.0m
Eagletac G25C2-II (stock): Weight 141.0g, Length: 150.6mm, Width: 39.6mm
Eagletac TX25C2: Weight 93.6g, Length: 120.4mm, Width (bezel): 31.6mm
Klarus RS11: Weight 158.0g, Length: 160mm, Width (bezel) 34.9mm
Nitecore MH25: Weight: 145.4g, Length: 160mm, Width (bezel): 40.0m
Nitecore P25: Weight: 171.3g, Length: 160mm, Width (bezel): 40.0m
Olight M22: Weight: 148.4g, Length: 144.8mm, Width: 41.2mm (bezel)
Sunwayman T21CS: Weight 161.9g, Length: 154mm Width (bezel): 41.4mm
Overall size and weight is similar to the Nitecore P25. This is slightly longer and heavier than some other lights in this class – due in part to to control ring on the SRT7 (and the charging dock on the P25).
Anodizing is a shiny black, with no chips on my sample. Labels are bright white and clear against the dark background. The SRT7 has a number of grip elements, starting with bands of knurling over the tailcap and body tube (I would describe this knurling as medium aggressiveness, comparable to the P25). Combined with all the ridge detail, overall grip is good. With either the included grip ring or pocket clip installed, grip and anti-roll should be more than sufficient.
The control ring has a fair amount of knurling on it, and I found it easy to identify by touch. Control ring feel is excellent – not too stiff, not too loose. There are also very clear "detents" that ring enters into before switching into other possible output modes (more on that in a moment – see my User Interface section for a discussion).
The SRT7 build is very similar to the P25, and shares its "tactical" focus. For example, these lights both feature head and tail springs (i.e., to be able to handle weapon recoil without momentary breaking of battery contact). Nitecore has mounted a physical reverse-polarity ring on the positive contact spring in the head, so only small button-top cells will work in this light. All of my small-button cells worked fine, except my Eagletac 3400mAh cells were a bit inconsistent (i.e., didn't seem to work at first, but now seem to be working ok) The battery tube is wide enough to take higher-capacity protected 18650 cells.
Tail screw threads are standard triangular cut, and seem of good quality. They are also anodized at the tail for lock-out. Interestingly, there are square-cut (or more precisely, trapezoidal) threads in the head region. Note that although the battery tubes look virtually identical, the P25 and SRT7 can only swap tailcaps, not heads (i.e., there is a different pattern to the thread design at the head-region of the body tube).
Tail switch is a forward clicky, with traditional feel, identical the P25. Lights can tailstand, and there are raised areas for the lanyard attachment. However, I found my sample fairly wobbly when tailstanding (although loosening of the tailcap retaining ring may help).
There is a low-voltage red LED warning indicator located on the head. This will flash to indicate when the batteries are running low.
The head is where things get really interesting:
The SRT7 has a very distinctive reflector/emitter combo. Overall dimensions are similar to the Nitecore P25 (i.e., same size opening and bezel ring, with relatively deep reflectors with a smooth finish). But as you can see, there are three equidistant cut-outs along the periphery or the SRT7 reflector that house tri-colored LED diodes. These wells are quite deep, and well placed to minimize any beam artifacts for the main white LED beam (see beamshots later in this review).
I've seen a few other lights with this arrangement, although they usually sport 5mm colored LEDs. In this case, each cut-out has a multi-diode arrangement, and all three produce the color of interest. Check out the images below.
The tri-LED effect is bound to produce some artifacts in the colored beam. Again, see the beamshot section later in this review for more info.
Note that the SRT7 uses a fairly common 40mm bezel opening diameter, so a number of possible beam diffusers will fit. Shown below is the Nitecore NFD40, but I personally find the Olight M21X/M22 is a more snug fit.
One comment here – the diffusers can also be useful for the tri-colored LEDs (as you will see in the beamshots below, artifacts can be an issue). However, depending the margin of the diffuser cover frame, this may block some of the colored output (i.e., the colored LEDs are at the periphery of the reflector).
Again, scroll down for some actual beamshots for this light.
The SRT7 has a forward tailcap clicky - press and release for momentary on, click for locked on.
Mode switching is controlled by the magnetic control ring in the head. As previously mentioned, the SRT7 features a continuously-variable interface for the main white LED. But there are actually quite a number of modes you can select on this model. Note that you can select your desired mode while the light is off, if you remember the sequence.
The various output modes on the ring are set or separated by very clear detents (i.e., the ring stays firmly in position, and needs a fair amount of force to move into the next mode). Starting at the far left (i.e., holding the light out in front of you, with the ring all the way to the left), as you turn the ring to the right (clockwise), you get the following outputs modes:
White Beacon > Police Strobe (flashing blue/red) > Blue > Green > Red > Standby off > Continuously-variable ramp (over ~110 degree turn of the ring between detents) > Max White > White Strobe.
Again, each mode is set in a clear detent of the ring, except for the continuously-variable ramp (which is between the Standby off and Max detents). This means that if you keep the ring between these two detents, you will never see any of the other modes. It is only if you exceed this range to the right (for Strobe) or left (for colored modes, and eventually Beacon) do you see any of these additional modes.
An interesting feature of the light is that it shows a "soft start" if you click it On with the control ring set to any level except Max (i.e., comes on low, and quick ramps up to the set level in under a second). Note that the light doesn't do this once you reach the Max level - there, it simply jumps straight to Max from Off. if I were to hazard a guess, Nitecore may have done this for those who like to have immediate momentary access to max output (i.e., for the "tactical" crowd). As has been pointed out in the commentary below, this is the same pattern as the Sunwayman V20C.
But what I like here is that turning the control-ring in the continuously-variable portion while On similarly shows a soft-start-like pattern - i.e., there is a slight lag for the brightness to "catch up" to the new set level. Scroll down for a discussion of the continuously-variable ramping pattern – this too is rather unique.
The video link below should help clarify the interface. I found it easy to get used to in practice – it is quite sophisticated, while being easy to learn.
For information on the light, including the build and user interface, please see my video overview:
Video was recorded in 720p, but YouTube typically defaults to 360p. Once the video is running, you can click on the configuration settings icon and select the higher 480p to 720p options. You can also run full-screen.
As with all my videos, I recommend you have annotations turned on. I commonly update the commentary with additional information or clarifications before publicly releasing the video.
As if all that weren't enough, the ramping pattern is where things get particularly exciting for me. Of course, if you aren't interested in all the technical explanation below, you can skip ahead to the beamshots - safe in the knowledge that the SRT7 ramp will seem quite "linear" to your relative perceptions.
Long time readers of my reviews will know that I have spent a lot of time categorizing the ramping patterns of different continuously-variable lights. The control mechanism can either be time-based (i.e., ramps over a range in a set time, with the ability to stop at any point), or distance-based (i.e., turn a ring to specific point to select an output, along a set degree range of levels). The SRT7 falls into the latter category, like most magnetic control ring lights.
But what truly separates continuously-variable lights is the ramping pattern – is it "circuit-linear" (meaning output changes directly proportional to current), or is some sort of "visually-linear" correction used (so that the light appears to ramp evenly across our perceptual range)? Early lights were typically circuit-linear, but this makes it hard to select relatively low output levels (i.e., due to the non-linear way we perceive output, these lights seem to spend most of their ramp at the near-maximal levels).
The common way to "visually-linearize" a ramp has been do a logarithmic adjustment in the circuit. Logarithms have long been used to try to compensate for a number of non-linear systems, including our relative visual perceptions (e.g. the stops of camera are logarithmic).
However, it turns out that a logarithmic adjustment is not accurate for our visual perceptions. While it may seem so over relatively narrow (and bright) output ranges, this relationship clearly breaks down when you go to more extreme levels (e.g., ultra-low levels). Extensive scientific research over the last several decades has revealed distinct power relationships that better correlate to our various relative sensory perceptions. For perceived brightness of a non-point source of light, the currently accepted linearization method is actually a cube root of output. For a full discussion of this - including detailed graphs and primary literature references - please see this post and the subsequent discussion.
To put the SRT7 in context to other continuously-variable lights of the same class, here is what my lightbox reports as you turn the ring:
The Jetbeam RRT21 is a classic example of circuit-linear ramp, and the Sunwayman V20C is good example of a logarithmic "visually-linear" ramp. The Niwalker NWK600N1 seems to use a hybrid approach, with a mainly circuit-linear ramp, but with a correction factor to adjust relative outputs near the maximal levels. Among these three, I definitely prefer the logarithmic-ramp approach of the V20C.
But you should be able to tell that there is something different about the SRT7. To help us figure out what that is, it is useful to correct the lightbox output by the actual correction factor that most closely correlates for how we perceive light (i.e., a cube-root). This is known as the Stevens’ power law relationship for perceived brightness, and is plotted below:
This is what you can subjectively expect to see when you handle the lights. As expected, the "visually-linear" V20C will subjectively spend a lot of time at the lower output levels, while the "circuit-linear" RRT-21 spends most of the range of the dial choosing between near-maximal outputs. While the V20C model is preferable, it likely won't seem consistently linear to you.
But notice how "linear" the SRT7 looks on this perceived brightness plot? That tells me that Nitecore is presumably using a cube-root correction factor instead of a logarithmic one for the SRT7 – as I have long argued for. It means that for practical purposes, the SRT7 will seem truly visually "linear" for your relative perceptions, at all levels.
It's nice to know that someone is actually reading these reviews. I hope we continue to see more lights with a cube-root visual correction factor.
As an aside, you will notice that the SRT7 doesn't go quite as low as some other continuously-variable lights. See my detailed output/throw summary tables later in the review for more info.
Also, if you turn the ring rapidly, keep in mind that there is a lag in how quickly it adjusts output (i.e., like the "soft start" effect from off). This wasn't a confound for my ramping analysis above, as I turn the ring very slowly to measure the ramp patterns.
There is no sign of pulse-width-modulation (PWM), at any level. I presume the light is current-controlled.
The signal is too low for my oscilloscope, but the Police Strobe pattern is interesting - it is a rapid strobe of numerous red flashes (over ~0.7 secs), followed by similarly rapid set of blue flashes (over ~0.7secs), in an infinitely repeating loop (i.e., alternating red and blue). It is apparently designed reproduce the effect of a police car's flashing red/blue lights. Maybe it's just me, but I don't think attempting to imitate a police cruiser is necessarily a very good idea for civilians.
The tactical strobe (white LED) is a very high pulse frequency strobe, of 22Hz frequency. But it also has an usual pulse width – as you can see above, there is a relatively short "on" phase (i.e. it is only on about ~25% of the time). This differs from most Strobes, which typically use a 50:50 pulse width (i.e., on for half the pulse, off for the half the pulse). But I often see shortened on-pulse durations in lights with really high strobe pulse frequencies.
In any case, you can rest assured that the strobe is extremely disorienting.
The beacon mode a single rapid flash, once every ~2.3 secs or so.
Thanks the to the tailcap clicky switch, you can always turn the light completely off (i.e., no standby current).
There is a standby position on the control ring, just below the continuously-variable ramp. I measured the current at this standby level as 430uA on a 1x18650 (although it periodically jumps to just under 4mA every few secs when the standby indicator lights up). As such, it is hard to provide an estimate for the "average" current. For a typical 18650 battery, I would expect you should still get at least several months before it would be fully drained. This is not unreasonable for short-term use – but I recommend you keep the light clicked off (or locked out) at the tailcap when not in current use.
For white-wall beamshots below, all lights are on Max output on an AW protected 18650 battery. Lights are about ~0.75 meter from a white wall (with the camera ~1.25 meters back from the wall). Automatic white balance on the camera, to minimize tint differences.
There really isn't much of a difference above - beam pattern of the SRT7 is very much in keeping with the other recent 18650 lights in this class. Note that overall output of SRT7 is not quite as high on 1x18650 as 2x sources (see output tables later in this review).
One thing that is quite impressive is the general lack of artifacts in the spill of the main white LED of the SRT7 (given those three colored LED cut-out wells). The heavily recessed wells have clearly done the trick here – you would be hard pressed to notice anything amiss from the white LED beam alone.
But let's see how the individual colored beams make out:
In a word, ugh. To be fair, ~0.75m is a ridiculously close distance to be using the light. But I kept the common distance to show you the variable nature of the artifact/interference pattern of the multi-LED setup. As you go out the greater distances, these artifacts become less noticeable, but they remain present.
If you are going to use the colored beams extensively, you may want to consider a good quality diffuser. This will cut the output to some degree – especially around the periphery, depending on how much of a frame the diffuser cover has (as explained earlier).
For outdoor beamshots, these are done in the style of my earlier 100-yard round-up review. Please see that thread for a discussion of the topography (i.e. the road dips in the distance, to better show you the corona in the mid-ground). FYI, any "streaks" you see across the images are bug-trails. Flying insects are often attracted to the bright lights, and their flight trails get captured as swirly streaks due to the long exposure time. Also, ignore any tint differences below – they are mainly due to the automatic white balance setting on the camera.
There really isn't much difference between these three lights in practice, so I'm bit surprised at how the beamshots look (i.e., the G25C2-II appears to have a throw and output advantage, and the M22 seems a bit dimmer than the other two). I think this is mainly a combination of tint differences with the auto white balance (i.e. M22 is warmer), and the exact focusing (i.e., less corona reflected on the road with the M22). In real life, I was not able to discern any significant difference in throw between these three light.
Note as well that all lights were on 1x18650. I have observed that the SRT7 is brighter on 2x sources. See my direct output and runtime measures below for more info.
All my output numbers are relative for my home-made light box setup, a la Quickbeam's flashlightreviews.com method. You can directly compare all my relative output values from different reviews - i.e. an output value of "10" in one graph is the same as "10" in another. All runtimes are done under a cooling fan, except for any extended run Lo/Min modes (i.e. >12 hours) which are done without cooling.
I have devised a method for converting my lightbox relative output values (ROV) to estimated Lumens. See my How to convert Selfbuilt's Lightbox values to Lumens thread for more info.
Throw/Output Summary Chart:
My summary tables are reported in a manner consistent with the ANSI FL-1 standard for flashlight testing. Please see http://www.flashlightreviews.ca/FL1.htm for a discussion, and a description of all the terms used in these tables. Effective July 2012, I have updated all my Peak Intensity/Beam Distance measures with a NIST-certified Extech EA31 lightmeter (orange highlights).
First observation is that the SRT7 is brighter on 2x battery sources than 1x18650. Both max levels are still within a comparable range to other high-output XM-L2 lights in my collection. Note that my estimated lumens at this level are consistently under-reported for many lights – I had few high output lights when originally calibrating my lightbox. As always, I recommend you use my estimated lumens as a relative guide to comparing lights in my collection, not as an absolute accuracy indicator.
One thing I can confidently say is that my SRT7 does not go down to the report "0.1 lumens" specified by Nitecore. My sample is at least an order of magnitude brighter than that (i.e., >1 lumen). I believe my lightbox is very well calibrated at this low lumen scale.
In terms of throw, the SRT7 is also quite similar to other high-output XM-L and XM-L2 lights in my collection. Throw is definitely good for the class.
UPDATE JULY 11, 2013: I've been asked to estimate the output of the colored LEDs. Note that my lightbox calibration is based on white LEDs, so I don't know if the relationship holds consistently for the specific colors. But using my standard white LED calibration, I get the following:
Lowest white level: 1.3 lumens
Red: 3.3 lumens
Green: 12 lumens
Blue: 6.1 lumens
These lightbox readings approximate what I see by eye, but again, can't say if the relative calibration holds for all specific colors.
Note: Unless otherwise stated, all my runtimes below are based on AW 2200mAh 18650 cells.
Again, you can see that the SRT7 is not quite as bright on 1x18650 as 2x battery sources. The light is well regulated, and there is the same double step-down pattern on Max as the P25, on all battery sources (i.e., there are two distinct, yet gradual, timed steps down during the Max runs). As before, you can always click off/on to restore initial max output.
Overall, the output/runtime efficiency is very similar to defined-level Nitecore P25, and several of my other current-controlled lights. For a continuously-variable light, this is an excellent showing.
UPDATE JUNE 16,2013: I realize the graphs above are a little crowded, so here is a direct comparison of 2xRCR and 1x18650, on Max:
As you can see above, there is a gradual drop-off over the first 6 mins (although you would never be able to see by eye). After the first step-down, the light keep a regulated level (indifinitely for 2xRCR, for a short period on 18650). At 20mins, another step-down occurs.
It is interesting that the 1x18650 and 2xRCR both step-down to the same level. In terms of the 18650 results above, I expect the newer higher capacity 18650s would probably stay at a regulated level longer, after the first step-down. But I haven't tested that yet.
UPDATE JUNE 17, 2013: Ok, here are the extra 18650 runtimes:
As you can see, the 3100mAh cell is able to maintain flat regulation of the full first 20 mins (plus an extra half hour later). Interestingly, the 3400mAh started to drop out of regulation a couple of minutes before the 20min step down (but also does an extra half hour at the lower level). Overall runtime is longer with the greater capacity cells, as expected.
So it seems to be very dependent on the type of cell you are using, in terms of how long the light can stay regulated.
There are no labels to indicate where you are on the control ring. If you want to turn the light on in a specific mode, you have to remember the mode sequence and count the number of detents before activation.
Flat-top cells will not work in the light. And even among small button top cells, you will need to have a significant protrusion. UPDATE: I originally reported that my relatively short button-top Eagletac 3400mAh cells didn't work in the light, but they do seem to be working now. I suspect these cells are right at the border of what the contact plate in the head with accept, so you may experience some intermittent issues with these particular cells on some lights.
The light has a physical on-off switch, so no standby current is present when clicked off or locked out at the tailcap. There is a Standby off detent on the control ring, which would drain a 18650 in a few months (if not clicked off or locked out).
As with the P25, the low-voltage LED indicator comes on within a few seconds on near-max output levels on a 1x18650 (even with a fully charged cell). This feature seemed to more accurately gauge power remaining with multiple cells, making me think it was confused by the high current drain on a single 18650 on Turbo.
The SRT7 is an impressive light – both for its feature set, and its well-thought-out implementation. Although there are a few minor points (see above), this inaugural member of the "Smart Ring Tactical" family shows a careful attention to detail on Nitecore's part.
I can clearly see the design heritage here – the SRT7 builds heavily on the physical frame of the P25 (which in turn drew from elements of the MH25). But the control interface is distinctive. I haven't seen a control ring with a visually-linear, continuously variable ramp on a Nitecore light since the IFE2 over 2 years ago. And I like the implementation here – the ring has a good feel, with sharp detents and smooth motion.
The nice thing about a control ring is you can always tell where you are ahead of time – before you turn on the light. That said, you do need to memorize the mode sequence here, which is a bit more complicated due to all the extra features. The only thing that might have helped is identifying mode labels on the head/ring, but I could see how that could clutter the look of the light (given the large number of modes available).
The feature set is certainly distinctive. The tri-colored LEDs for red, green and blue produce fairly bright output for this type of light (which is probably due to each of the three emitters containing all three diodes for each color). While there are significant artifacts in the colored beams, it is remarkable how little interference these provide for the main white LED. Frankly, I don't imagine users would notice any really difference in the main beam profile compared to the Nitecore P25.
The implementation of the various blinking modes is also good, placed at the extremes of the ring. If it were me, I would probably have placed Beacon next to Strobe, but that's a minor quibble. While I am not a "tactical" person myself, I expect those that value these sorts of things will generally like the versatility of this interface.
The ramping feature is probably unique in my testing, incorporating two novel features. The most obvious of these is a "soft-start-like" lag in adjusting output (i.e., the light doesn't jump with a quick flick of the ring, but ramps up to the new ring-set level). This isn't actually unique though - the Sunwayman V20C does the same thing. But more subtle and distinctive is the actual ramping pattern - based on my analysis, it appears that Nitecore is using a cube-root adjustment scheme to produce a visually-linear appearance. As I have long argued, modern perceptual science research has shown that this is more consistent with our actual perceptions of light (compared to the common logarithmic adjustment scheme, which is just an approximate attempt to "visually-linearize"). This is different from the V20C, which uses a logarithmic ramp.
Performance is also top notch – regulation pattern and overall output/runtime efficiency is comparable to the defined-level, current-controlled P25. That's an impressive showing for a continuously-variable light.
I know this has been a rather long review, but there is a lot to talk about here. Bottom line, I think Nitecore has done a good job with the implementation of their new SRT feature set. It has been a fun light to play around with.
SRT7 provided by Nitecore for review.