- Stephen Knight
Flashlight Review: Convoy S21F
Updated: Mar 7
Convoy already produce some of the best flashlights/torches for night photography illumination. The Convoy S21F is based on the popular S21D, but with a side switch, USB-C charging, and adjustable colour temperature (CCT).
The Convoy S21F was purchased with my own funds. Product links in this review are non-affiliate. This review is written from the perspective of a night photographer and flashlight enthusiast.
The Convoy S21F is an evolution of the impressive 2,150 lumen Convoy S21D, which is renowned for impressive maximum and sustained high colour rendering (CRI) output in a compact flashlight. Instead of the Convoy S21D's tail switch, the S21F has a side switch (with Convoy's side switch UI) and a USB-C charging port which makes the light much more consumer friendly. Whilst the quad LED S21D is available with 7 different correlated colour temperature (CCT) options of the Nichia 519A LED emitters, the S21F has adjustable CCT from warm white 2700k to coolish white 5700k, with 2 LEDs of each. Many flashlight enthusiasts might call this tint ramping, but it is actually CCT ramping.
The light arrived in Convoy's (too) minimalised packaging, with a lanyard, and surprisingly for a Convoy - instructions! No side clip or O-rings were included. The 33.1mm head diameter is slightly larger than the S21D and slightly smaller than the S12. Body diameter is 27.5mm, and the length is 121mm. The side e-switch and USB charging port are placed on opposite sides of the light on the head. The USB charging port has a soft plug for protection.
The light requires flat top 21700 rechargeable Li-ion batteries. As the driver is an 8A (max) constant current driver, most 21700s will have enough power for this light. I would thus recommend the high capacity Samsung 50E, BAK N21700CG-50, or Molicell M50A for use with this light. Use of lower capacity, higher current 21700 batteries will not see a significant increase in output as the light (thankfully) doesn't use a FET driver. The tail cap unscrews for battery insertion. Charging current is claimed to be 2A, and a full charge from empty took 3 hours for a 5000mAh battery. Charging terminated correctly at 4.19V. USB-A (Qualcomm QC3.0 charger) to USB-C, and USB-C (Samsung Super Fast charger) to USB-C charging worked successfully.
The S21F is compatible with Kaidomain D37 diffusers, and U-shaped tripod mounts. Due to the location of the side switch, it isn't compatible with backlight scanners - the S21D is my choice for that use case. Again, due to the side switch, this light is not suitable for use with light painting systems.
The Convoy S21F has a side e-switch and uses a slightly modified version of the ramping user interface (UI) found on other Convoy lights such as the S21E, M21D/E/F, and M3-C. The main features of this user interface include adjustable CTT (ramping), ramping or stepped brightness (4 brightness levels), turbo mode, moonlight mode, hidden strobe, and electronic lockout. It should be noted that Turbo mode is an extra mode above 4/4 brightness, which is different to other Convoy side switch lights I've tested. General use is:
Single click from off - turns on (last mode memory, note: default is low after mechanical lockout).
Single click from on - turns off.
Hold from on - light ramps or steps through brightness levels (low, medium, high, higher).
Click, then hold from on - colour temperature ramping.
Hold from off - turns on in moonlight mode (not memorized).
Double click from on/off - turbo mode.
Triple click from on/off - strobe (double click to cycle strobe>SOS>beacon, single click to exit to last mode memory).
Quadruple click from off - enter/exit tactical momentary mode (turbo mode will be on only when switch is depressed).
5 clicks from off - battery check (light flashes out voltage).
6 clicks from off - switch between ramping and stepped brightness.
10 clicks from off - enter/exit electronic lockout mode. (Note: the light can also be mechanically locked out by slightly unscrewing the tail cap).
I quite like this user interface for illumination purposes. Positives include choice of ramping or stepped brightness, last mode memory, and voltage check. The fast click>hold timing for CCT adjustment takes a bit of getting used to, and I did quite often accidentally turn the light off instead. Brightness ramping alternates between up/down, and is still too fast at lower brightness levels. The CCT ramping adjustment alternates between up/down, and there is no indication to denote the end or midpoints. It takes 8 seconds for a 2700k to 5700k CCT adjustment. As there are no stepped CCT adjustments, it is difficult to select a consistent CCT between the end points. Unlike LED panel lights, there is no screen displaying the selected CCT to the user.
The side switch has a light ring that illuminates green when on, red when on and voltage low, red when charging, and green when fully charged. The light is off when the flashlight is off and not charging. I found the side switch difficult to find in the dark, and I prefer the more tactile raised switch on the S21E. I also found the head shape allows the light to roll much more than the S21D.
Beam and Output
Instead of the S21D's fixed colour temperature/CTTs (available in 2700, 3000k, 3500k, 4000k, 4500k, 5000k, and 5700k), the S21F has two 2700k and two 5700k LED emitters. By adjusting the brightness of these two sets of LEDs, the CCT can be adjusted anywhere between 2700k warm white and 5700k coolish white.
The Convoy S21F uses the same sized TIR optics as the S21D, and the excellent >95CRI Nichia 519A LED emitters for excellent colour rendering. Whilst the S21D is available with 4 different optics from 10 degree clear to 60 degree beaded, the first batch of S21F was only available with 60 degree beaded optics for a very smooth floody beam. The diffused hotspot is 60 degrees, and the spill beam is 170 degrees. With a peak beam intensity of 3.5Kcd, the light better for near field floody illumination. The choice of default 60 degree optics may be to adequately diffuse the two sets of LEDs with different CCTs, which it does very well. It is possible to swap the optics for other options from Convoy (30 degree beaded, 10 degree beaded, 10 degree clear). Testing with the 10 degree beaded lens at 3700k showed noticeable CCT shift, with a warm hotspot, and cooler spill beam.
Brightness (lumens), colour rendering (CRI), colour temperature (CCT), and tint (DUV) were measured at 10 seconds after light turn on. The latter three were hotspot measurements using an Opple Light Master 3 Pro.
S21F 3/4 mode 2700k - 564 lumens, 97.6 Ra CRI, 2728k CCT, -0.0027 DUV.
S21F 4/4 mode 2700k - 1167 lumens, 98.3 Ra CRI, 2552k CCT, -0.0010 DUV.
S21F 1/4 mode 5700k - 20 lumens.
S21F 2/4 mode 5700k - 65 lumens.
S21F 3/4 mode 5700k - 636 lumens, 97.8 Ra CRI, 4988k CCT, -0.0042 DUV.
S21F 4/4 mode 5700k - 1337 lumens, 97 Ra CRI, 4886k CCT, -0.0033 DUV.
S21F 3/4 mode approx. mid-point - 585 lumens, 97.2 Ra CRI, 3796k CCT, -0.0057 DUV.
S21F 4/4 mode approx. mid-point - 859 lumens, 97.1 Ra CRI, 3761k CCT, -0.0056 DUV.
S21F Turbo mode - 2090 lumens, 97 Ra CRI, 3580k CCT, -0.0060 DUV.
S21D 3/4 mode 5700k - 852 lumens, 98 Ra CRI, 4771k CCT, -0.0024 DUV.
S21D 4/4 mode 5700k - 2150 lumens, 97.4 Ra CRI, 4866k CCT, -0.0026 DUV.
Update 07/03/23 - the CCT at the 5700k is noticeably cooler in the second batch of S21F at 5326k CCT on 4/4 mode. DUV -0.0059 and 97.3 Ra CRI.
Notes on these results:
The S21F differs from other side switch Convoys by having a Turbo mode above the 4 stepped brightness levels, but only at the theoretical mid-point of approx. 3700k (measured 3580k).
All tint measurements are below the BBL (slightly magenta). There is a green AR lens in front of the TIR optics which may be slightly lowering the tint/DUV towards magenta.
As expected due to the laws of physics, there is a slight magenta tint shift when two CCTs are being mixed. Whilst some flashlight enthusiasts like a "rosy" tint, I prefer neutral tints for night photography, particularly when using multiple light sources. It should be noted that budget pocket LED panel lights such as the Weeylite RB9 also experience this magenta tint shift. More professional pocket LED panel lights such as the Pilotcine Atomcube RX7 can compensate for the green to magenta tint shift. The magenta tint is not as extreme as with Nichia 219B LEDs.
The coolish white 5700k CCT output is actually more of a neutral white 4700k-5000k range, possible due to relatively low current/emitter, TIR optics, and tint bin.
The mid-point (approx 3700k) on 4/4 mode performs less than expected. Note: I tested this 3 times!
There is a large step between 2/4 and 3/4 brightness. 2/4 brightness should be ideally around 150-200 lumens instead of 50-60 lumens.
Step-down testing was also interesting:
S21F Turbo mode (3700k) - step down from initial 2090 lumens occurred from 55 seconds, with a low point of 379 lumens at 3mins, a rebound to 901 lumens at 4 mins, and sustained 530 lumens from 6 minutes.
S21F 4/4 mode 5700k - step down from initial 1337 lumens occurred from 55 seconds, with a low point of 456 lumens at 2 mins, and a rebound to a sustained 642 lumens from 4 minutes. Runtime was 2hr40mins until low voltage warning flashes started with a 5000mAh battery.
S21F 3/4 mode 5700k - brightness was sustained at approx. 636 lumens.
Notes on these results:
This is the first time I've seen temperature management on a Convoy flashlight overshoot the sustained temperature, and then rebound.
After the rebound, the classic Convoy constant sustained brightness occurred - this is very useful for consistency between consecutive photos in night photography.
Sustained brightness is not as good as the Convoy S21D 8A 519A and Acebeam E70-AL 95CRI flashlights, but still pretty good and similar to the Convoy S21E and Lume Cube 2.0.
Even after step-down, the S21F's measured illuminance was 1250 lux/1m. This is identical to the 40W Zhiyen M40 (4300k, 100% output) and much brighter than the impressive 12W Weeylite RB9 (5000k, 100% output) which measured 450 lux/1m. So the Convoy S21F has potential as a handheld or tripod mounted photography portrait light (for key or fill lighting).
No waveform rippling or PWM was detected by my phone camera.
Excellent value for money ($US33).
Very high colour rendering >97 Ra CRI.
Adjustable colour temperatures/CCT can be useful for photography use.
Respectable sustained brightness.
Diffuser and U-shaped tripod mount compatibility.
Very floody beam (60 degree optics) is useful for portrait photography.
USB-C charging input.
No fixed colour temperature/CTT version.
Brightness ramping too fast at lower brightness levels.
No stepped CCT adjustment, not great for consistency.
No indication of mid or end points when adjusting CCT.
Side switch is not tactile enough in the dark.
Large brightness step between 2/4 and 3/4 brightness.
The S21F is a bit of a niche light. Having adjustable colour temperature (CCT), and USB-C charging potentially allows a photographer to use one flashlight to obtain a range of different CCTs. This makes it very useful for travel purposes. With a very floody beam, it has enough output to be used as portable portrait lighting, and matches the brightest pocket LED panel lights in terms of lux/distance. Sustained brightness is not as good as the similar sized Convoy S21D. Sustained brightness is however still quite respectable, and similar to the Convoy S21E and Lume Cube 2.0.
As with many other flashlight enthusiasts I was expecting the S21F to be a fixed CCT, USB-C charging, and side switch version of the awesome S21D. I really hope that Convoy produce a fixed CCT model with S21D sustained brightness performance.
Convoy S21F Product Page (no battery)
Convoy S21F Product Page (with battery)
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