The SP35T is a tactical-style, general-purpose flashlight running on a single included 21700 battery. It features both tactical and general user interface options.

1. Introduction
2. Manufacturer Specifications
3. Package Details
4. Build
5. User Interface
6. Circuit Measures
7. Emitter Measures
8. Beamshots
9. Testing Results
10. Runtimes
11. Pros and Cons
12. Overall Rating
13. Preliminary Conclusions
14. Acknowledgement

Introduction

The SP35T is a popular mid-range model from Sofirn. Equipped with the XHP50.2 emitter, it is rated for relatively high output in the 1×21700 class – similar to many competing models that I’ve recently tested from other makers. What really caught my eye here though was the tactical tailcap switch. That’s not something you see very often any more, outside of the larger “tactical” lights from Wurkkos and Sofirn.

Given the very interconnected (and sometimes interchangeable) nature of parts across Wurkkos and Sofirn lights, I thought the SP35T might be an interesting one to test. Could this be a “Goldilocks” model that strikes just the right balance between output and performance?

Let’s see how it performs in my testing.

Manufacturer Specifications

Note: as always, these are simply what the manufacturer provides – scroll down to see my actual runtimes.

Feature	Specs
Maker	Sofirn
Model	SP35T
Emitter	XHP50.2
Tint
Max Output (Lumens)	3,800
Min Output (Lumens)	5
Max Runtime	220 hours
Max Beam Intensity (cd)	19,625 cd
Max Beam Distance (m)	280 m
Constant Levels	5
Flashing	Strobe, SOS, Beacon
Battery	1x21700
Weight (w/o battery)	-
Weight (with battery)	87 g
Length	139.5 mm
Head Diameter	28 mm
Body Diameter	-
Waterproof	IPX8 2m

Package Details

Unlike the modern “cellphone box” style packaging of the newer models from Sofirn and Wurkkos, my SP35T came in the same basic retail packaging as my old IF25A. Oh well, it’s what inside the box that counts I guess. There I found:

• Sofirn SP35T flashlight
• Sofirn-branded 5000mAh 21700 battery
• Pocket clip
• Wrist lanyard
• USB-C charging cable
• 2 Spare O-rings
• Manual

It’s a decent package for a “budget” build, but I would like to see a holster included. FYI, Wurkkos sells an inexpensive holster (small size for ~$2 USD) that fits this light well.

Build

From left to right: LiitoKala 21700 (5000mAh), Vapcell 21700 F56 (5600mAh), Emisar D4K, Imalent MS03, Convoy S21E, Skilhunt M300, Wurkkos WK15, Wurkkos TS22, Sofirn SP35T, Cyansky P25, Nitecore P20iX, Acebeam E70.

At just under 140mm, the SP35T is one of the tallest general-purpose 1×21700 lights I’ve handled. This is the side effect of the tactical forward clicky switch (and dual spring design). This makes the light very suitable for tactical purposes, but it does mean you have to accept greater length. As someone with above-average sized hands with long fingers, I find the light comfortable to hold and use in either overhand or underhand grip – but some may find it a bit long.

The SP35T definitely shares a lot close design similarities to recent compact Wurkkos lights I’ve handled. This is not surprising, since these lights come off the same manufacturing production lines (i.e., Sofirn is the OEM manufacturer for Wurkkos).

The tailcap physical forward clicky switch does indeed look and feel identical to the Sofirn C8L that I recently reviewed. It has a pleasantly firm action, with a solid click and predictable firm traverse. It could just be sample variability, but I found the switch on my recent Wurkkos TD01 to be comparatively “soft and squishy” – I like the firmness of this SP35T sample. There are two raised tailcap guards that can serve as the lanyard attachment point. And just like my C8L, it is able to tailstand stably (my TD01 would not).

Tailcap threads are square-cut and anodized, with good feel. Thanks to the anodized tailcap threads, you can easily lock-out this light by a simple twist of the tailcap.

As an aside, the whole tailcap assembly here won’t fit on the TD01 – but it does fit and work on my Wurkkos TS22 perfectly.

There is a raised side-mounted electronic switch on the side of the head, with red and green LEDs underneath to show charge status. Feel and traverse of the electronic switch is very similar to a lot of Wurkkos and Sofirn lights – it’s ok, but could be a bit tighter/firmer (i.e., hard switch covers always have some degree of play).

The side switch shines a bright red when charging the battery through the light’s USB-C charging port (green when fully charged). The port is located on the opposite side from the switch, under a rubber cover. The cover fits pretty well on the SP35T (just like the C8L) – not too too tight, not too loose. I expected waterproofness is reasonable.

There is a reasonable amount of knurling on the light – not super aggressive, but more than most, and certainly enough to help with grip. With the various other design elements and cut-outs, I would say grip is excellent. Thanks to included clip, the light will not roll on its side. Anodizing looks to be good quality for type II, with no damage on my sample. I would describe the finish as matte.

Inside, the light comes with a Sofirn-branded standard-sized 5000mAh 21700 battery, with a slightly raised flat-top. There is a good size spring in the head, ensuring good contact.

This is a solid and well-designed light, with good grip and handfeel. It is a bit longer than most in this class, which is something to keep in mind.

The SP35T comes with a XHP50.2 HD emitter, in cool white tint apparently (I didn’t see any options to select a specific tint). The reflector is fairly shallow and heavily textured (heavy orange peel, HOP). There doesn’t seem to be any kind of anti-reflective coating on the lens.

As expected, there is some tint/colour shifting across the periphery of the beam, with a cool white hotspot surrounded by a yellowish spill except for a purplish shift near the edge of the periphery. This is a well-known issue with HD emitters of the XHP family, especially apparent on the XHP50.2. The heavily textured reflector seems to be help even it out it somewhat – it’s not as pronounced as most that I’ve seen.

The bezel is crenelated black aluminum. Scalloping is not too aggressive, so you can headstand stably.

User Interface

The SP35T has a straightforward user interface, and one that is identical to the Sofirn C8L and Wurkkos TD01. Like many “tactical” lights, you have two sets of possible modes; Mode Group 1 for General use, and Mode Group 2 for Tactical use.

To switch between groups, press-and-hold the side switch for >3 secs when On.

Mode Group 1 (default) available levels: Eco, Low, Medium, High, Turbo, Strobe, SOS, and Beacon.

Mode Group 1, from OFF:

• Tail switch, partial-press: Momentary On in last memorized mode.
• Tail switch, single-click: Turns On in last memorized mode.
• Tail switch, double-press: Turns On in last memorized mode and then jumps to Turbo (click to stay locked-on in Turbo). You have be very rapid on the double-press to jump to Turbo.
• Side switch, press-and-hold: Nothing – but if you click the tail switch while holding down the side switch, the light will activate in Eco mode.
• Side switch, single-click: Nothing.

Mode Group 1, from ON:

• Tail switch, partial-press: Nothing.
• Tail switch, single-click: Turns Off.
• Side switch, press-and-hold (3 secs): Switch to Mode Group 2 (see below)
• Side switch, single-click: Steps up to the next non-Turbo constant output mode (in sequence, Eco > Lo > Med > High).
• Side switch, double-click: Turbo.
• Side switch, triple-click: Strobe.
  • Side switch, double-click when in Strobe: Cycle through in sequence Strobe > SOS > Beacon (with no mode memory).

Mode 1, Mode memory:

Yes, for non-Turbo constant output modes.

Mode 1 Shortcuts:

• Eco mode: Press and hold the side switch while turning on at the tail switch.
• Turbo mode: Double-click the side switch from On, or double-press the tail switch from Off.

Mode 2 available levels: Medium, Turbo, and Strobe.

Mode 2 functions basically as a stripped-down “tactical” version of Mode 1. The main differences are:

• Single-click of the side switch from On only selects between Medium and Turbo now.
• Double-click of the the tail or side switch goes to Strobe instead of Turbo.
• There is no level memory now.

Otherwise, the two modes function the same way.

Battery indicator:

When first activating the light, the indicator on the side switch shows the battery voltage  (lasts for ~5 secs):

• Solid green: ~70-100%
• Flashing green: ~40-70%
• Solid red: ~10-40%
• Flashing red: 0-10%

Mode memory:

Yes, in the Mode Group 1 for non-Turbo constant output modes. There is no memory in the Mode Group 2.

Shortcuts:

• Mode Group 1: Yes, for Eco, Turbo and Strobe (see above).
• Mode Group 2: Yes, for Eco and Strobe (see above).

Low voltage warning:

Yes, the main light will step down as the battery is running low. It will then turn Off at ~2.95V

Lock-out mode:

Yes, but physically – you lock-out the light by a twist of the tailcap.

Reviewer Comments:

As with the C8L and TD01, I think this is a reasonable dual-mode UI for a tactical light, with a general mode set and a tactical mode set.

The multiple-press functionality of the tactical tailcap switch is a cute feature, if you feel you need a direct shortcut to Turbo from Off. With the firm clicky switch, I found I was able to do this reliably well. But for non-tactical types, I find doing a double-click of the side switch from On even easier.

I prefer General Mode Group, for its general usefulness and versatility. But I suppose “tactical” people will like the lack of mode memory in Tactical Mode Group 2.

Circuit Measures

Pulse-Width Modulation (PWM):

Eco:

Low:

Med:

High:

Turbo:

There is low frequency circuit noise on all levels, including Turbo, on the SP35T. It is definitely not PWM (note the simple sine wave below), but is at an an unusually low frequency of 167 Hz according to my soundcard oscilloscope. Shown below on a shorter timescale for the Hi mode.

This is certainly different from the C8L, which was completely noise free. Even the TD01, which had circuit noise on all levels except Turbo, was at a more typical high frequency of ~5kHz.

Again, this is not a problem per se, as it was completely undetectable in practice (i.e., I couldn’t even see it when shinning on a fan or running water). But I do find it very unusual, and am not sure what to make of it. Typically, I find this doesn’t bode well for regulation or output/runtime efficiency.

Strobes:

Strobe:

Strobe alternates between 7 Hz and 11 Hz every ~1.5 secs or so. Very distracting.

SOS:

A standard SOS mode, relatively slow.

Beacon:

A single flash beacon once every 2 secs (0.5 Hz).

Charging:

The switch button shows solid red when the light is charging. Changes to solid green when the charging is complete.

Resting voltage <3.0V

Resting voltage >3.0V

The SP35T does not have a two-stage charging feature, as seen on many modern lights (i.e., where there is a lower initial charging rate when the cell is heavily discharged). Mind you, neither does the C8L. The initial charging rate here is ~1.75A, which slowly rose to ~1.85A after a few minutes. I presume it continued to climb from there. This is a pretty high charging rate for the class, and will charge a 21700 cell quickly.

Standby / Parasitic Drain:

None. That is one of the nice things about a physical clicky switch, no standby current. 🙂 And you can always lock-out the light by a twist of the tailcap, to prevent accidental activation.

Emitter Measures

In this section, I directly measure key emitter characteristics in terms of colour temperature, tint, and colour rendition. Please see my Emitter Measures page to learn more about what these terms mean, and how I am measuring them. As tint in particular can shift across levels, I typically stick with the highest stably regulated level for all my reported measures.

As explained on that page, since I am using an inexpensive uncalibrated device, you can only make relative comparisons across my reviews (i.e., don’t take these numbers as absolutely accurate values, but as relatively consistent across lights in my testing).

SP35T on Hi:

The key measures above are the colour temperature of ~5725K, and a negligible positive tint shift (+0.0103 Duv) to a very slight greenish-yellow at this temperature. For CRI (Ra), I measured a combined score of 58.

These values are consistent with the performance of a cool white XHP50.2 emitter, and match my visual experience of this light. Note that there is a tint shift to more yellowish spill, with purplish spillbeam edge, as is common on XHP50.2 HD emitters.

Beamshots

All outdoor beamshots are taken on my Canon PowerShot S5 IS at f/2.7, 0.5 secs exposure, ISO 400, daylight white balance. The bend in the road is approximately 40 meters (~45 yards) from the camera. Learn more about my outdoor beamshots here (scroll down for the floody light position used in this review).

Click on any thumbnail image below to open a full size image in a new window. You can then easily compare beams by switching between tabs.

As you can see above, the SP35T has a narrower spill than most lights in this class, and somewhat lower output (although to be fair, three of the lights above are XHP70.2 lights). It is a very clean beam though, with little evidence of chromatic/tint aberrations.

Testing Results

My summary tables are generally reported in a manner consistent with the ANSI FL-1 standard for flashlight testing. In addition to the links above, please see my output measures page for more background.

All my output numbers are based on my home-made lightbox setup. As explained on that methodology page, I have devised a method for converting my lightbox relative output values to estimated lumens. Note that my lightbox calibration seems to run higher than most hobbyists today, but I’ve kept it to remain consistent with my earlier reviews (when the calibration standard was first established).

My Peak Intensity/Beam Distance are directly measured with a NIST-certified Extech EA31 lightmeter.

SP35T Testing Results

Mode	Spec Lumens	Estimated Lumens @0sec	Estimated Lumens @30 secs	Beam Intensity @0sec	Beam Intensity @30secs	Beam Distance @30secs	PWM/Strobe Freq	Noise Freq	Charging Current <3V	Charging Current >3V	Parasitic Drain	Weight w/o Battery	Weight with Battery	CCT (K)	Duv	CRI
Eco	5	2.1	2.1	-	-	-	No	164 Hz	1.75 A	1.85 A	No	84 g	153 g	-	-	-
Low	100	80	80	-	-	-	No	165 Hz	1.75 A	1.85 A	No	84 g	153 g	-	-	-
Med	500	385	380	-	-	-	No	166 Hz	1.75 A	1.85 A	No	84 g	153 g	-	-	-
High	1,500	1,050	1,030	-	-	-	No	167 Hz	1.75 A	1.85 A	No	84 g	153 g	5,725	0.0103	58
Turbo	3,800	2,950	2,850	11,200 cd	10,400 cd	204 m	No	168 Hz	1.75 A	1.85 A	No	84 g	153 g	-	-	-
Strobe	3,800	-	-	-	-	-	7.0-14.8 Hz	168 Hz	1.75 A	1.85 A	No	84 g	153 g	-	-	-
SOS	500	-	-	-	-	-	No	168 Hz	1.75 A	1.85 A	No	84 g	153 g	-	-	-
Beacon	3,800	-	-	-	-	-	2.25 Hz	-	1.75 A	1.85 A	No	84 g	153 g	-	-	-

The SP35T clearly has very inflated specs across all its output levels, as measured in my lightbox. It is probably even worse than the numbers above suggest, as I know my lightbox’s relative calibration is generously high for modern high-output lights. This finding is not entirely surprising, since the max output ratings in particular were not realistic for the XHP50.2 emitter.

My NIST-calibrated luxmeter is accurately calibrated to an absolute standard, and similarly reports much lower beam intensity on Turbo (~25-30% less than spec, which is comparable to what my lightbox reports for overall output measures).

To view and download full testing results for all modern lights in my testing, check out my Database page.

Runtimes

As always, my runtimes are done under a small cooling fan, for safety and consistency. To learn more about how to interpret runtime graphs, see my runtimes methodology page.

According to reports online, the SP35T is supposed to have a buck driver – but I don’t see any evidence of that. Looking at the Med and Hi mode runtimes, it looks like a basic FET driver – and one that performs remarkably similar to the XHP50.2-equipped Wurkkos WK15 that I currently have on hand for testing. I presume these two lights are in fact using the same basic driver. This is a bit disappointing compared to the excellent flat voltage-regulated Wurkkos TS22.

There is one thing that is very different on the SP35T though – the wide oscillations in output on Turbo mode. Presuming this was due to the thermal sensor reacting to my cooling fan, I did a separate test without cooling, as shown in the lighter green above. It is clear that the cooling fan is having a big difference, as the light runs fairly consistently at the much lower level once step-down occurs without cooling. But it is interesting that the oscillations do eventually re-appear later in the run.

To show this more clearly, here are the two Turbo runtimes – with and without cooling – on a longer timeframe:

This is pretty unique in my experience. The step-down from Turbo level is to quite a bit lower level than usual (down to ~450 lumens in my lightbox, just slightly above Med level). Eventually, as the light cools, it starts to step up in output, with widening swings.

By the way, I know the swings under a cooling fan seem a lot more extreme above, but they are not so noticeable in real life. Below is an expanded runtime, to show you that a typical ramp up and back down under cooling actual takes about 7 mins. Here is how it looks in practice:

In the rising stage, you won’t notice the gradual shift over time, it is that slow. But on the ramp down, you are likely to notice the light is dimming fairly quickly.

All that to say, I think this light would benefit from a less sensitive thermal sensor – and a lower step-down level to start with (i.e., ~450 lumens is very low for a modern light).

Pros and Cons

Pros	Cons
The light has a solid build, with a tactical forward clicky switch in the tail and a side electronic switch.	Circuit is not voltage-regulated, producing a slowly decreasing output instead of flat runtimes.
The light has a serviceable dual mode set user interface, identical to the Sofirn C8L and Wurkkos TD01.	The circuit is also noticeably less efficient then other current-controlled lights with flat regulation.
Price is reasonably low.	The turbo mode steps down to a much lower level than most lights, and oscillates considerably in output (likely due to a poorly calibrated thermal sensor).
	XHP50.2 HD emitters produce well known tint shifts across the beam, with a yellowish spill and purplish spillbeam edge.
	Output specifications are clearly very inflated.

Overall Rating

Preliminary Conclusions

The SP35T is certainly a solid light, with a very decent physical build and good user interface. The presence of a forward clicky tactical switch here is great, if you are a fan of that design. The user interface is certainly very serviceable, being identical to the C8L.

But as the pros and cons list above demonstrates, the circuit performance is disappointing here. Sure, it produces a reasonable amount of light for a reasonable amount of time – but its performance just doesn’t compare to the well-regulated and efficient C8L or Wurkkos TS22. But the SP35T doesn’t even compare well to other simple FET driver-based lights – due to the unusually low step-down level on Turbo, and the repeated oscillations back up to higher output as it cools.

Moreover, the rated output specs are way off on this light (as in, at least 25-30% below spec, if not more). Its rare nowadays to see such a large mismatch between published specs and actual performance. Since many make their purchasing decisions based on published specs, this is very disappointing.

The XHP50.2 HD emitter is known for a lot of tint/chromatic variation across its beam, and this example is no different. That said, I do find it a bit better than typical, likely due to the heavily textured reflector here. But to put it simply, I think this light would benefit from both an emitter and circuit upgrade.

At the end of the day, I like the physical build (and forward clicky tail switch). The user interface is also quite serviceable. But the circuit performance is sub-standard compared to Sofirn’s other offerings, and to other lights in this class – both in terms of overall output and output/runtime efficiency. And the odd behaviour on Turbo after step-down needs to be corrected. But it still is a reasonable amount of light for a reasonable amount of time, in absolute terms.

Acknowledgement

The SP35T was supplied by Sofirn for review. As always, all opinions are my own and the light received the same rigourous and objective testing as all other lights that I have reviewed. At the time of review, this light retails for ~$30 USD (~$40 CDN) on sale on the Sofirn website here.