Convoy S21D Nichia 519a Flashlight Review

Convoy S21D Nichia 519a Flashlight Review

The Convoy S21D flashlight is now available with Nichia 519a emitters! This quad uses a single 21700 cell and has great output. Read on!

Official Specs and Features

Here’s a link to the Convoy S21D Nichia 519a flashlight product page. I don’t know that this light can actually be purchased at the moment, though.


It’s hard to say what versions there are due to the light currently being unavailable. At the very least, though, there were multiple CCT’s available for this emitter in the S21D.


My order indicates this light was around $40. But again, it doesn’t seem to be available right now.

Short Review

The Convoy S21D scratches a few itches very nicely. It offers Nichia 519a emitters, for one thing. In a quad, very floody output for another. And uses a 21700 cell, which is very popular too. The quality is great and the output is so nice from these emitters!

Long Review

The Big Table

Convoy S21D Nichia 519a Flashlight
Emitter: Nichia 519a (4500K)
Price in USD at publication time: $38.99
Cell: 1×21700
“100%” Runtime Graph “35%” Runtime Graph
LVP? Yes
Switch Type: Mechanical
On-Board Charging? No
Claimed Lumens (lm)
Measured Lumens (at 30s) 1717
Candela per Lumen 2
Claimed Throw (m)
Candela (Calculated) in cd (at 30s) 168lux @ 4.495m = 3394cd
Throw (Calculated) (m) 116.5
Claimed CCT 4500
Measured CCT Range (K) 4000-4200 Kelvin
Item provided for review by: Convoy Store
All my Convoy reviews!

^ Measurement disclaimer:  I am an amateur flashlight reviewer.  I don’t have $10,000 or even $1,000 worth of testing equipment.  I test output and such in PVC tubes!!  Please consider claims within 10% of what I measure to be perfectly reasonable (accurate, even).

What’s Included

Convoy S21D Nichia 519a Flashlight what's included

  • Convoy S21D Flashlight
  • Liitokala 5000mAh 21700
  • Lanyard (attached)

Package and Manual

Convoy S21D Nichia 519a Flashlight box

There is no manual.

Build Quality and Disassembly

Convoy S21D Nichia 519a Flashlight

Convoy is very highly regarded by flashlight enthusiasts for having great build quality and low prices. This Convoy S21D Nichia 519a is no exception. It’s great!

Both head and tail come off the light. The tail parts are held in place by a brass retaining ring. The tail has a nice beefy spring.

Convoy S21D Nichia 519a Flashlight tailend view

The head has a long brass button – no spring.

Convoy S21D Nichia 519a Flashlight head brass button

The cell tube is not reversible, and will not work in the “wrong” orientation.  One end is anodized, and one is unanodized.  The anodized end is the tail end.  Also, both bodies have their own o-rings.

Convoy S21D Nichia 519a Flashlight head and tail off Convoy S21D Nichia 519a Flashlight head and tail contacts Convoy S21D Nichia 519a Flashlight head cooling fins

Size and Comps

Body diameter: 27.2mm
Head diameter: 32.1mm
Length: 126.5mm

Weight (with cell): 171.4g

If the flashlight will headstand, I’ll show it here (usually the third photo).  If the flashlight will tailstand, I’ll show that here, too (usually the fourth photo).

Convoy S21D Nichia 519a Flashlight in hand

Here’s the test light with the venerable Convoy S2+.  Mine’s a custom “baked” edition Nichia 219b triple.  A very nice 18650 light.

And here’s the light beside my custom engraved TorchLAB BOSS 35, an 18350 light.  I reviewed the aluminum version of that light in both 35 and 70 formats.

Convoy S21D Nichia 519a Flashlight beside the TorchLAB BOSS 35 (custom engraved)

Shorty, just a joke!

Convoy S21D Nichia 519a Flashlight joke photo, no cell tube

Retention and Carry

Only a lanyard is included for carry of the Convoy S21D flashlight.

It ships attached, as seen below, from the factory. This is the wrong way. 😉

Convoy S21D Nichia 519a Flashlight lanyard misinstalled

Just one side of the tailcap has lanyard holes.

Convoy S21D Nichia 519a Flashlight lanyard holes

When correctly installed, the lanyard does not interfere with tailstanding.

Convoy S21D Nichia 519a Flashlight lanyard installed

There’s no pocket clip or nylon pouch or anything else included for carry of the S21D.

Power and Runtime

The Convoy S21D is powered by a single lithium-ion cell. The tube supports a single 21700 cell. My package included the cell seen below. LiitoKala is a well-regarded brand, and this cell should suit the light nicely. It’s a 5000mAh flat top unprotected 21700.

Convoy S21D Nichia 519a Flashlight included 21700 cell

The cell is installed the usual way – positive terminal toward the head.

Convoy S21D Nichia 519a Flashlight included 21700 cell

Here are a couple of runtime tests.

Convoy S21D Nichia 519a Flashlight runtime graph Convoy S21D Nichia 519a Flashlight runtime graph

The squiggle at the end of each test indicate that the main emitters are blinking a low voltage warning.

Modes and Currents

Mode Mode Claimed Output (lm) Claimed Runtime Measured Lumens Tailcap Amps
100% 100% 1717 7.47
35% 35% 706 1.97
10% 10% 0.53
1% 1% 0.07
0.1% 0.1% 0.03

Pulse Width Modulation

None of the output levels in this mode group (the default group) use PWM.

For reference, here’s a baseline shot, with all the room lights off and almost nothing hitting the sensor.  Also, here’s the light with the worst PWM I could find.  I’m adding multiple timescales, so it’ll be easier to compare to the test light.  Unfortunately, the PWM on this light is so bad that it doesn’t even work with my normal scale, with is 50 microseconds (50us).  10ms5ms2ms1ms0.5ms0.2ms.  In a display faster than 0.2ms or so, the on/off cycle is more than one screen, so it’d just (very incorrectly) look like a flat line.  I wrote more about this Ultrafire WF-602C flashlight and explained a little about PWM too.

User Interface and Operation

There’s a single switch on the Convoy S21D.  This is a reverse mechanical clicky.  A reverse clicky has the benefit of allowing mode changes while the light is on.  But this also means that the switch does nothing until it is on – no momentary action whatsoever.

Convoy S21D Nichia 519a Flashlight switch Convoy S21D Nichia 519a Flashlight switch profile

The action on these switches is fantastic. It’s like clicking a good Bic Clic Stic pen – just a rewarding action.

This driver is known as “Biscotti” and has a bunch of mode groups. Actually, this is reportedly not true Biscotti – that’s why I called it “Fauxcotti” above. It’s nearly the same though. Mode memory can be turned on or off (yay!), and programming is easy!  But there are simply too many possibilities for me to list the UI in a table as I usually do. Here is Simon’s flow chart for the UI.

Here’s the official guide for the Biscotti firmware:


From the mode group selection above, the light ships in mode group 1.  You’ll want to switch it to mode group 2 quickly of course.  🙂  And I always turn off memory if possible (and it’s possible here!).  I made a first pass at my own flow chart, which you can see below.

zeroair reviews biscotti flow chart revision 1

If something’s wrong (or even just “unclear”) in there, please let me know!

LED and Beam

The Convoy S21D has four Nichia 519a emitters. We call this a “quad.”  That emitter is all the rage lately, and if you continue reading I think you’ll see why. But the summary is that it has great output with great CCT and great CRI – it’s just a great emitter.

Convoy S21D Nichia 519a Flashlight quad emitters with TIR

Note the optic used here – it’s dimpled, and makes the output very floody!

The bezel is smooth, so light does not escape when headstanding.

Convoy S21D Nichia 519a Flashlight headstanding

The parts are easy to unscrew and gain access to. When I got this light I had to tighten the bezel just a bit. After doing so, the modes didn’t work exactly right – I had to back the bezel off just a very tiny bit for the modes to cycle right.

Convoy S21D Nichia 519a Flashlight bezel removed Convoy S21D Nichia 519a Flashlight bezel removed and on Convoy S21D Nichia 519a Flashlight beamshot

LED Color Report (CRI and CCT)

Without even zooming in or clicking those images below you should be able to get a good idea – look at the circles, to start with. See how nearly the red circle matches the black circle? The black circle is essentially “perfect.” That means that the Nichia 519a is “nearly perfect” – in fact, it’s practically as perfect as we can get in a flashlight. Now translate that into CRI – the CRI is above 96 in every output level. At the lower levels (when not being driven very hard) the CRI is hitting 98!


These beamshots are always with the following settings:  f8, ISO100, 0.3s shutter, and manual 5000K exposure.

Tint vs BLF-348 ( 219b version) (affiliate link)

I keep the test flashlight on the left, and the BLF-348 reference flashlight on the right.

I compare everything to the 219b BLF-348 because it’s inexpensive and has the best tint!


What I like

  • Reasonable price for a quad 519A light.
  • Great way to get this new Nichia 519A emitter in the CCT of your choice
  • Build quality is great, especially for such a low-cost light
  • Very even floody output

What I don’t like

  • Had to manipulate the bezel to get the modes to work consistently
  • No pocket clip option
  • No other carry options


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6 thoughts on “Convoy S21D Nichia 519a Flashlight Review”

  1. Now if Hank could put out a 21700 version of the D4, we’d be all set. One Biscotti, one Anduril. It appears that Convoy is doing a bit better with dissipation given the additional meat on the head, smart move. Hopefully Hank is watching!

  2. Thanks for the review.
    Is this the same host as the S12 and S16?
    The measurements you gave for the host size are different from what the Convoy store quotes (34.6/27.4mm head/body, 134mm length)

    1. Noted, thanks. Someone on YouTube showed a photo of the S21D, S12 and S16 next to each other so I know now how they compare.

  3. Thanks for nice review.
    I see, “%%” modes is not precisely %% from max. current.

    Can you measure currents in “20%” and “50%” modes ?

    1. oops, you wrote “Tailcap Amps”.

      Can you measure currents in “20%” and “50%” modes at same (with 10 and 35 modes) accu voltage ?

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