Convoy S21A (Short Technical Review)

The new Convoy S21A (with SST-40 LED) can be found on the manufacturer’s website HERE. It is similar in size/appearance to the Convoy S2+, but is slightly larger, due to the larger 21700 battery. Information about the SST-40 LED (6,500K) can be found HERE, (thanks to BLF member djozz).

This review will include:

(1) lumens measurements

(2) runtime graphs

(3) temperature readings

(4) PWM test

(5) beam pattern/tint


Manufacturer spec for high is "up to 2,300 lumens".

The S21A has only four brightness levels, which according to the manufacturer is because;

is very suitable for ordinary users

Note that Simon has hinted (HERE) at the future availability of the Crescendo user interface. Details on how Crescendo works HERE.

Using my Texas Ace Calibrated Lumens Tube:

Level 4 (100%) 1,770 lumens (0 sec) – 1,635 lumens (30 sec)

Level 3 (30%) – 695 lumens (0 sec) – 675 lumens (30 sec)

Level 2 (3%) – 82 lumens

Level 1 (.1%) - 0 lumens (could not measure)


Framed by two S2+ for size comparison.

Framed by two S2+ (front view).

Framed by two S2+ (back view).

The S21A comes with an orange peel reflector.

Runtime Graphs:

High (no cooling)

High (with COOLING)

Level 3 (30%)

Level 2 (3%)

Temperature readings

As seen in the "high" runtime graphs, the S21A starts throttling down immediately, to control heat. According to the Convoy website;

Temperature readings taken with a Fluke 62 Max Plus IR Thermometer.

As you can see, the temperature gets HOT rather quickly. After fifteen minutes, the light was too hot for me to hold.

If the Crescendo user interface becomes optional (which has a thermal setting), it may solve this issue.


NONE was measurable (at any brightness level) using an OSRAM BPW34S PIN photodiode and an oscilloscope. This confirms the manufacturer claim “no frequency can be seen in any mode

Beam pattern

The SST-40 LED tint is noticeably green at level two (82 lumens), but is not as noticeable on level 3 and 4. This greenish tint was also noticed on the Convoy S11 (which also uses the SST-40).

The orange peel reflector helps smooth out the center beam.

Conclusions so far:

This light has the potential to be as popular as the S2+. Unfortunately, it suffers from a few things I don’t like.

  1. The brightness level spacing is very wide. There are only four brightness levels from .1 to 100%. For example, there is no brightness level between 80 and 600 lumens. A more customizable UI would be nice, similar to Biscotti. While the design goal was "is very suitable for ordinary users", it may leave flashaholics a bit disappointed. However, again, Simon has hinted at the future availability of the Crescendo user interface. Edit update - there is now a twelve mode version available HERE
  2. The greenish tint from the SST-40 LED is rather noticeable, especially at lower levels (82 lumens).
  3. Temperature management could use some user control. Most people will not be able to hold this light for long on high. High should be considered as a turbo mode only. If the Crescendo user interface is released (which has a thermal setting), it may solve this issue. I do not personally like my lights to get too hot. All my S2+ lights have only three chips (7135), which keeps them warm only. Of course, this is all a matter of opinion/preference.

Been waiting for this. Totally agreed that the mode spacing is too wide. There should be an output at around 150-400 lumens there.

Would a Carclo quad optic (diameter 24mm) fit inside the head?
this one would be a great candidate for a quad mod.

Pretty sure those KD quads will fit, that alone has me more interested in buying an S21 now

i get a driver with Crescendo UI ,
it’s attiny13,
i have a question ,
totally no memory function if i use attiny13?

I've heard there is no room for a memory function on attiny13 if using Crescendo. Too bad.

how does it cycle through the levels? is it half click per level or is it half click and hold while it cycles through all levels and release once its at the one you want?
would the lumen output be closer to the advertised output if you used a higher discharge battery such as the samsung 40t?

Hi Simon,

Why don’t you talk to Toykeeper ?

A half click cycles through levels.

Using a Samsung 40T produced the same output levels. Per my SC700d review HERE, the 48G was able to drive the Zebralight SC700d to 3,000 lumens with no problem (so 2,000 lumens would not be an issue on the S21A).

thanks. guess ill buy some Samsung 50e’s since it makes no difference.

My quick video demo on Convoy S21A w/ SST-40:

Hi, I decided to check out a "S21" light as sold on ebay and it must be similar to the one being discussed. On the side it says "Manta Ray" and S21. Not a bad light for $22.28 shipped from China.

Battery Configurations: 1x21700 or 18650 3.7v, mine seems happy with a 18650.

Options: Luminus SST-20-W LED (6500K/5000K/4000K/3000K) - I ordered the 5000K which looks OK, has kind of blue/purple rings around the outside. Would have got the 4000K if I new what I know now. Emits a whine at the lower modes but I can only hear it close to my ear.

Ebay Description: S21 luminus SST-20-W stepless dimming light 21700/18650 Battery LED flashlights.

I also ordered a "Convoy S2 + Mit Luminus SST20 4000K Military Flashlight Hunting Tactical Torch" which looks similar and is cheaper after shipping, but it's not here yet.

-Dick Locke p.s. I'd post a picture but not able to, only a link? New to this forum so not sure what's up with that.

p.p.s. Let's see if I can add a pic...


@dtlocke, post a link, and I’ll show you what to do.

Embed a pic - looks like this will embed a pick of the S21 “Manta Ray” from ebay…

S21 Manta Ray from Ebay

Thanks for the review.
Ordered one. When it comes will give feedback.

I have feeling that this will be very stupid question, but

I have just got new s21a from simon

is it OK if the light head is ratling? whole inside part is moving and glass is free to rotate and move…

Shouldn't do that.

(1) Make sure the pill is screwed all the way down. There are two notches on the pill - you can use needle-nose pliers to screw it all the way down.

(2) Make sure the O-ring wasn't left out (behind the lens).

max temps on convoy s21a

Would be interested a comparasion betwen S21A and S2+,same power config Driver and Led
wich of them dissipates better heat

My Convoy S21A.