Kraken KR-S40 Underwater Strobe Review

This Underwater Strobe is Smaller Than a Can of Coke! 

The Kraken KR-S40 might be the smallest—and most affordable—underwater strobe on the market. Priced at just $359, it costs less than half the price of popular “pro” strobes like the Sea & Sea YS-D3 Duo and the Marelux Apollo S. Weighing in at only 200 grams, the KR-S40 delivers 40 Ws of power and a 60-degree beam angle—making it an ideal strobe for macro photography. And with Kraken’s upcoming snoot attachment, it’s poised to become a serious rival to the popular Backscatter Mini Flash and snoot combo.

At Bluewater Photo, we were among the first to test the KR-S40 in the field. We took it diving in the cold, murky waters of West Seattle—home to wolf eels and hermit crabs—and were impressed by how well it performed. As you’ll see in the sample images below, the strobe produced vibrant colors and sharp detail. For just $359, the image quality it delivers is an absolute steal.

A hermit crab grabs a mate. Photographed with the Nikon Z8 and a Kraken KR-S40 Strobe. f/18, 1/160, ISO 500

Kraken KR-S40 Specifications

• Power: 40 Ws
• Color temperature: 6000K
• Guide Number: 16
• Modes: S1, S2, no TTL
• Beam Angle: 60°
• Recycle Time: 1.5 Seconds to Full Power
• Power Levels: Five (40ws, 20ws, 10ws, 5ws, 2ws)
• Target Light: 500 lumens
• Depth rating: 100m
• Battery: 1x 21700 Battery
• Batterlife: 600 full power flashes
• Dimensions: 62mm x 63mm x 130mm
• Weight: 530g on land & 200g under water
• Fiber optic triggering only with Sea & Sea style fiber optic port

Playing with some wide angle compositions with the Kraken KR-S40 strobe. While it's not the widest strobe, I was able to capture some compelling images with great color.

Kraken KR-S40 Top Features

Ultra-Long Batterylife

I’ll admit it—I don’t fully understand the physics behind the Kraken KR-S40. Somehow, with just a single 21700 battery, Kraken claims it can deliver up to 600 full-power flashes. I was skeptical at first—but after nearly a week of diving with the strobe, that skepticism disappeared.

I didn’t need to charge it once.

While I probably didn’t hit the full 600-shot mark, I easily fired off several hundred flashes across multiple dives. Even with downtime between dives, the battery just kept going. It never felt like it was running low, which is something I rarely say about compact strobes in this price range.

A "Macro Oriented" Beam

A quick glance at the spec sheet makes it clear: the Kraken KR-S40 is designed for macro. It delivers 40 watt-seconds of power with a 60-degree beam angle and a 6000K color temperature. That beam isn’t wide or powerful enough for most wide-angle situations—especially in bright, tropical environments where you need to match strong ambient light. But in darker conditions, like the cold waters of the Pacific Northwest, it can still deliver surprisingly good wide-angle results.

For macro, the strobe really shines. I was able to shoot at apertures up to f/18 without pushing the ISO too high—ideal for getting sharp, detailed images. My one minor critique is the beam color: at 6000K, it leans slightly cool. This can actually enhance subjects in green, temperate waters, but I occasionally found myself warming up images in post. That said, the colors still look natural—and in some cases, even more vibrant. The blues in the wolf eel shot below, for example, really pop.

A wolf eel photographed with the Kraken KR-S40 strobe

A Compact and Durable Design

The most striking feature of the KR-S40 is its size. When Kraken shipped me the strobes, they arrived—two of them—in a padded envelope. Each one fit easily in the palm of my hand and was smaller than a can of soda.

The strobes are machined from anodized aluminum, making them impressively durable and able to withstand rough surf, bumps, and scratches. Underwater, they weigh just 200 grams; above water, a bit more—around half a kilogram.

The controls are straightforward: a single button activates the modeling light, and a simple switch lets you cycle through power levels.

A sea pen photographed with the Kraken KR-S40 strobes

White and Red Modeling Lights

The modeling lights on the KR-S40 are a thoughtful addition. The white light outputs 500 lumens—not enough for serious video work, but sufficient for capturing short clips, as shown in the video above. Kraken also includes a red modeling light option, which is great for approaching skittish subjects that don’t detect red light underwater.

Conclusions

The Kraken KR-S40 is an impressive little strobe that punches well above its weight—both literally and figuratively. With its compact size, durable build, intuitive controls, and long battery life, it’s an ideal choice for macro shooters and travel-friendly dive kits. While it’s not built for wide-angle in bright conditions, it performs surprisingly well in low-light environments like the Pacific Northwest. Add in the red modeling light and the upcoming snoot attachment, and the KR-S40 becomes a serious contender for underwater photographers looking for high performance on a budget.

For just $359, it’s one of the best-value lighting tools we’ve seen in years.

A skeleton shrimp photographed with the Kraken KR-S40