Sofirn SD03

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Sofirn SD03 Specifications & measurements

Brand & Model	Sofirn SD03
Flashlight category	Diving light
Battery config.	1*18650
Switch type	Side only
Dimensions:
Length	126 mm
Head diameter	34 mm
Weight with battery	150 g
LED & Beam
LED type	Luminus SFT-40
High CRI	No
Focusable beam	No
Features
Onboard charging	No
Power bank	No
Specifications and measurements
Specified output	1,800 lm
Measured output (30sec)	1,267 lm
Max. measured output (turn on)	1,323 lm
Specified beam distance	447 m
Measured beam distance (30sec)	336 m
Specified beam intensity	49,616 cd
Measured beam intensity (30sec)	28,200 cd
Overall rating	3.5 stars
Review publication date	January 2025

Beginning in 2016-2017, Sofirn (named after his wife), was founded by Qidong Yang and was passionate about their customers and wanted to provide something of great value for all users with a wide variety of designs and applications. Their goal is to bring light to the world and make SOFIRN a well-known and a trusted brand offering a complete range of premium quality designs at affordable prices.

Since then, SOFIRN has expanded and added some of the best known and talented engineers within the Flashlight industry to their family, subsequently, releasing tons of new models.They have also created a presence and following by making custom units for fans and friends at “Budget Light Forum” (BLF), which proved to be very popular. Having collected a few Sofirn flashlights over the years I can always expect something very fun, bright and easily pocket-able.

Here comes another Sofirn Flashlight with a specific need in mind, or task at hand if you will. This one is in the diving light category. 

I was excited to see the Sofirn SD03 Diving Light come around my way for a review as I love all flashlights and this is definitely one of those. This Sofirn SD03 is the successor to the SD06, which is essentially the same light, but a little bit bigger, with it being the 21700 version. Now, we get an even smaller one! I am no scuba diver, but figured I could always jump in the water with it, for testing purposes of course!! I may not be diving a 100 meters but if I was, I could take and use the Sofirn SD03! I feel a swim coming on! 

An additional cool quote from Sofirn at no charge to you:

“Trust SOFIRN, we will stay with you, as we hope you will with us, our collective future will be brighter!”

What’s in the package

For today’s review, the retail packaging from Sofirn is the typical lackluster, brown box special when it comes delivered to your door. Even less impressive, the light is just wrapped in bubble wrap and laid in with all the extras that come along for the ride. All resting on a slice of foam at the bottom of the box. All fine but me, I generally don’t mind this as the company can usually put more time and money into the light itself versus fancy retail packaging, thus generally keeping the costs lower for us, the end-users. So for this one, the warm fuzzy feeling comes from finally getting the light out of the packaging and getting it in the palm of your hand. Ahh, the best part! 

After removing from the bubble-wrap, you finally get your paws on this smaller-sized, 18650 diving light. The included battery is placed inside the host with a battery insulator present to prevent connection and obviously, it is to be removed before lift-off. 

Inside my box-o-fun came all of the following items:

• Sofirn SD03 Diving Light
• Sofirn 18650, 3000 mAh battery
• USB-C Cable
• Poly-ion battery charger (4.2v/ 0.75a)
• Nice Lanyard w/ push button slider
• 2 – spare o-rings
• Instruction Manual

Unwrapping and pulling out your Sofirn SD03, you finally get a real-feel for how small this diving light actually is. It is a slick feeling, AL6061-T6 aluminium alloy, making it an anti-corrosive flashlight with milled ridges wrapping the diameter of the light. These aid in grasping the light for use. There is similar milling at the business end to aid in heat management.

Also towards the business end is the magnetic, rotary-type switch that rotates from the locked to the unlocked position for the mode activation. The rotary lockout switch’s magnetic contact also aids in moisture mitigation, not having any extra holes in the body that would allow water infiltration for this IP68 rated flashlight. Be cautioned here as any magnetic contact around the rotary switch can activate the light. Even with the flashlight in the locked position, touching the area around the switch with a magnet can/ will turn it on. Not a deal breaker but unusual and thought I would mention it.

The Sofirn SD03 body unscrews towards the head of the light (not at the tailcap) with an abundance of smooth, square threads. There is also a double-set of o-rings here again, aiding in waterproofing this diving light.

At the tailcap end of the light is a loop structure that would make a great place for the included lanyard…but… IT DOESN’T FIT! You can’t attach the lanyard (which I will mention is actually rather nice with a metal clasp) anywhere to this diving flashlight. A definite miss here as this seems like a necessity for a diving light….But, it appears after further investigating on my behalf, that you could insert the cord through the loop and wrap the lanyard back thru the end to be able to attach it, not utilizing the at nice clasp at all. 

This metal loop at the tail-end of the SD03 also keeps it from tail-standing with ease. You could probably balance it, but it’d better be flat where you’re setting it down. Speaking of setting it down, it isn’t going to roll away if you do lay it down due to the protruding button switch. There is no pocket clip or any other attachments.

But, an included accessory with the Sofirn SD03 is a “USB lithium battery charger” that works to charge the included Sofirn 18650 battery, along with a few other sized cells you might have. This is handy if you don’t already have a way to charge these wonky-sized (to a normal, non-flashlight enthusiast) 18650 batteries. Thanks Sofirn!

Use cases for the Sofirn SD03 Diving light would be the somewhat obvious, all your underwater adventures where you need a flashlight! Rated for up to 100m underwater, the SD03 will provide lighting in different output modes with ease. Even with the use of gloves, operation of the SD03 is simple and easy to manipulate. Just takes a press. 

Sofirn says they are in the business of making things right if something is wrong with your flashlight. Their warranty is as follows: 

• -If your Sofirn product has any defect as the result of the materials or workmanship we want to make it right!
• -Within 30 days of purchase: Contact the original seller for repair or replacement.
• -Flashlights: Within 1 year of purchase: Contact Sofirn for repair or replacement via Email: 

 [email protected]

-Batteries: Within half a year of purchase: Contact Sofirn for repair or replacement via Email:  

 [email protected]

-At first instance we attempt to resolve the issue. In the unlikely event of a faulty product we may advise customers to return the product to Sofirn for repair or replacement. This warranty does not cover normal wear and tear, modifications, misuse, negligence, accidents, improper maintenance, or repair by anyone other than an Authorized retailer or Sofirn itself.

The Sofirn SD03 is rocking the ever-popular Luminus SFT40. This LED is domeless and is generally a strong contender when it comes to output and throw especially. This version coming with the bright white 5000k temperature. There does appear to be a slight green tint to our sample that with each higher mode, becomes less green. Not-uncommon for SFT40’s to become cooler at higher currents.

There is a nice smooth, deep reflector gathering all of the lumens with our SD03. It generates a nice bright hotspot that throws rather well. The hotspot then fades to the spill quickly, but with soft edges. There is a lot of usable spill for up close lighting needs while still providing good throw. It is a rather large spill area, especially in the higher mode. Smooth reflectors and SFT40’s go hand in hand. There is also glass covering this along with the appropriate o-ring in the head for water mitigation. While we are at the business end, the bezel is smooth without any crenulations so no underwater hand-to-hand combat with the SD03.

More details: 

• LED Type: Luminus SFT-40
• High CRI: No
• Focusable beam: No

Spectral measurements:  

Measurements were taken using an Opple Light Master IV or to measure the flashlight beam in complete darkness at 10 meters away using the included fully charged Sofirn 18650, 3.7v, 3000 mAh Li-ion battery.

Mode:	CCT:	CRI Ra:	duv
High	4718K	–	0.0002

A positive DUV “above” the curve, exhibits more of a green tint, whereas a negative DUV indicates that the source is “below” the Planckian locus (blackbody curve, aka BBL), potentially giving a red/ blue tint.

Dimensions: 

Sofirn SD03	Millimeters	Inches
Length	126 mm	5.0 in
Head diameter	34 mm	1.3 in
Body diameter	23 mm	0.9 in

Dimensions are rounded to the nearest millimeter and the nearest tenth of an Inch.

Weight: 

Sofirn SD03	Weight in grams	Weight in oz
Without battery:	104 g	3.7 oz
With battery	150 g	5.3 oz

Weight is rounded to the nearest gram and tenth of an Oz.

Flashlight size comparison with its competition:

Group 1: Sofirn SD03, Sofirn SC18, Sofirn Q8 Plus

(family photos)

Group 2: Sofirn SD03 (sft-40), Emisar D1 (sft-40), Convoy L21B (sft-40)

(all sft-40 LEDs)

Lockout for the Sofirn is pretty straight forward. Rotate away from the locked position on the magnetic rotary dial and that’s it, you’re ready to shine. Then, simply press the button to turn this diving flashlight on in the last used mode. Each press of the button will change the light to the next available mode. 

Typical low, medium and high outputs as usual for this one. The button has a deep springy feel and is easy to manipulate, even with gloves on. The hard part, you will find when using the SD03, is going to be turning it off. It’s a simple action as you just press and hold the button. That’s it….but he trouble comes when trying to turn it off.

You are going to forget and change modes. It is inevitable and will get ya at some point. Maybe it’s just me, but it always feels counterintuitive to hold down the power button to turn off a flashlight. I can never remember that on the first try, but I won’t admit it. 

Again, a single click will get the light on and continuing to click will change modes. Hold down the power button to turn it off and rotate the dial to lock it back up! That’s all there is to it!

Available modes: 

• Low, Medium, High

Available blinky modes:

• None

From OFF:

• Single click: On in last used mode

From ON:

• Press and hold: Power Off 
• Single click: changes modes

Mode memory:

• Yes – last used mode.

Shortcuts:

• None

Strobe/blinkies

• None

Lock-out mode: 

• Switch lockout (rotate)

PWM

• None noticeable to eye

Additional/summary info on the UI: Just a heads up really, if you have the SD03 on and running, you CAN change the lockout switch back to “locked” and the light will stay on. It will also not turn back off until you “unlock” it again. (this would be the opposite of a lockout, would this be lock-in?) I digress

The Sofirn SD03 includes a single Sofirn 18650, 3.7v, 3000 mAh Li-ion battery. Sofirn has even included a Poly-ion charger that accepts 26650, 18650, 16340, and 14500 cells . Now you are able to charge your included 18650 powered, Diving Flashlight. Thank you Sofirn! Charging via the included charger at 4.2v/ 0.75a, takes a little over 4 hours from empty to full (4h 25min).

Battery level indicator:

• Solid green:Fully charges
• Solid red: charging

Batteries	Details
Compatible batteries	18650’s
Incompatible batteries	non-18650
Low voltage protection/warning	none
Onboard Charging:
Onboard charging	No
Power bank functionality	–
USB-C to USB-C charging	–
Max power of USB charger (port)	–
Max power measured	–
Final battery voltage (charged)	–
Avg. onboard charge time	–

Lumen measurements

How Lumens are Measured: Understanding ANSI FL1 Standards How Lumens are Measured: Understanding ANSI FL1 Standards: The ANSI FL1 standards specify that output in lumens should be measured 30 seconds after turning on, as this is the standardized time for measuring brightness according to the industry standard. This is why we focus on this part in our measurements. The ANSI FL1 standards require an ambient temperature of 22 ± 3°C. We record the ambient the ambient temperature to identify potential reasons for any observed discrepancies.

Lumen measurements were taken using my 50cm homemade integrating sphere (IS) and a REED R8100SD Data Logging Light Meter (with a measurement range up to 100,000 Lux). The IS has been calibrated using a 1lumen.com calibrated S2+ as a comparable reference source and the included fully charged Sofirn 18650, 3.7v, 3000 mAh Li-ion battery

Mode	Specified output	Turn on	30 sec.	10 min.
Low	300	348 lm	347 lm	344 lm
Med	1,000	906 lm	902 lm	526 lm
Turbo	1,800 lm	1,323 lm	1,267 lm	616 lm

*Turn-on and 30 second measurements are done manually, while the 10-minutes readings comes from the runtime graph. This is our standard approach, though some reviewers may choose a different approach.

Ambient temperature during testing:

•  20.5°C

Battery Life: Runtime graphs

How Runtimes are Measured: Understanding ANSI FL1 Standards About ANSI FL1 runtime standards: The runtime is measured until the light drops to 10% of its initial output (30 seconds after turning on). This does not mean that the flashlight is not usable anymore. The last column shows how long the light actually works till it shuts off. If there is a + symbol, it means that the test was stopped at that particular point, but the light was actually still running. This happens on certain occasions, with certain drivers, firmware, or batteries.

Runtimes were measured using the REED R8100SD Data Logging Light Meter (with a measurement range up to 100,000 Lux) and the included fully charged Sofirn 18650, 3.7v, 3000 mAh Li-ion battery

Mode	Specified runtime	Runtime (ANSI FL1)	Time till shut off*
Low	4h	3hrs 47mins	3hr 47mins
Med	3h	2hrs 45mins	3hrs 01min
High	1h 30min	1hr 28mins	2hr 46mins

*The last column reflects the total runtime until the light turns off. A “+” symbol indicates that the test was stopped at that point, but the light continued to run. This typically occurs with certain drivers, firmware, or battery types.

Coming in VERY close to the specified ANSI runtimes, the Sofirn SD03 times were right at the spec’d time. This is good to see and appreciated from any lighting company!

Peak beam intensity and beam distance measurements

About Peak beam intensity: Understanding ANSI FL1 Standards About peak beam intensity The calculated value of distance in meters at which the flashlight produces a light intensity of 0.25 lux. (0.25 lux is about the brightness of a full moon shining on an object). This means that the intensity has decreased so much, it becomes difficult to see darker objects, or objects that don’t reflect light. The columns ‘Meters’ and ‘Yards’ use rounded numbers.

Throw measurements were taken outdoors in complete darkness at 10 meters using the Dr. Meter LX1330B Digital Illuminance Light Meter, with a 0-200,000 measurement range for accurate lux readings, converted to candela. All measurements were taken at 30 seconds for most accurate measurements in accordance with ANSI measurement ratings.

Mode	Specified intensity	Specified beam distance	Candela measured	Meters	Yards
Low	9,850 cd	198 m	7,500 cd	173 m	189 yd
Medium	27,333 cd	331 m	20,200 cd	284 m	311 yd
High	49,616 cd	447 m	28,200 cd	336 m	367 yd

Ambient temperature during testing:

• 12.2 °C 

Surprisingly, candela numbers for the SD03 did not quite hit the mark here. In person the SD03 still shines well with the punchy lil throwy beam from that sft40. But, I did have higher hopes for this smooth, deep reflector.

Beamshots were taken using a Samsung Galaxy s23+ with the camera in “Pro” mode. Settings as follows:

• ISO 200, 0.5sec, WB 5000k
• Distance to fence is 28m

Beamshots of the following flashlights compared:

• Sofirn SD03
• Sofirn IF23 Pro
• Emisar D1K
• Convoy L21B (sft-40)
• Convoy S21A

Please note that the following beamshots are mainly intended to showcase the beam pattern and beam quality, rather than overall performance. These images are typically taken directly after activation, and in different seasons or weather conditions, and therefore do not fully represent its overall performance. In few cases the camera settings are even different and therefore not meant for performance comparisons. For accurate performance metrics, such as output, beam distance, and runtimes, you need to look at the performance section of this review.

Disclaimer: This flashlight was sent to us for review at no cost by Sofirn. We have not been paid to review, nor have we been holding back on problems or defects.

Buy your Sofirn SD03 here

1lumen selects and reviews products personally. We may earn affiliate commissions through our links, which help support our testing.