SFT40 vs SST40: How LED Design Changes Flashlight Throw and Beam Shape

Two flashlights can share the same lumen rating and still throw a beam that behaves nothing alike. One puts a wide pool of light on the ground a few yards out; the other sends a tight, punchy hotspot hundreds of meters downrange. Lumens don't explain that difference — the LED does, and specifically the tiny optical package sitting on top of it.

SFT40 and SST40 are two of the most common high-power LEDs in modern flashlights, including several current Fenix models. They're both made by Luminus, both put out serious brightness, and they're genuinely different in how they shape a beam. Here's what actually separates them, what flashlight testers have found when they've measured the two side by side, and which current Fenix lights use each one.

The Real Difference: What's Sitting on Top of the LED

An LED emitter isn't just a bare chip — it has a small optical package covering the light-producing surface, and that package is what changes how a reflector can shape the beam.

The SFT40 uses a flat window over a small emitting surface. A smaller, more concentrated light source gives a reflector more to work with when it's building a tight, directional beam — which is exactly why SFT40 shows up in throw-focused flashlights. The SST40 uses a domed package instead, which spreads light across a wider angle before it ever reaches the reflector. That's not a downgrade; it's a different design goal, and it tends to produce a broader, more even beam that's genuinely useful for general-purpose, close-to-medium-range lighting.

Neither LED decides the final beam on its own. Reflector size, lens shape, drive current, and the flashlight's overall design all factor in — which is why two flashlights using the exact same emitter can still throw very differently.

Why the SFT40 Usually Throws Farther — and Why "Usually" Matters

Beam distance depends on candela (how concentrated the light is), not just total lumens. A flood beam can put out thousands of lumens spread across a wide area, while a tighter beam with fewer total lumens can still travel much farther because more of that light is concentrated in one direction. That's the whole reason a flat-window emitter like the SFT40 tends to out-throw a domed one at the same lumen figure — the reflector can form a tighter hotspot from a smaller apparent source.

But the gain isn't automatic or huge. In one independent test that compared both LED options installed in the same flashlight body and reflector, the SFT40 measured roughly 50% higher peak intensity than the SST40 — a real difference, but testers noted the SFT40's advantage grows most in a light with a larger head to work with, and that in a more compact body, the total-output loss can offset much of that throw gain. In practice, the two can end up closer in usefulness than the spec sheets alone suggest.

Testing has also shown the SFT40 pulling further ahead of the SST40 at higher drive currents — above roughly 7 amps — thanks to better thermal behavior in that range, which is part of why the SFT40 shows up more often in higher-output, direct-drive-style throwers.

How Fenix Uses Each LED

Fenix pairs each emitter with the kind of flashlight it actually suits, and the specs bear that out:

Fenix TK11R — SFT40, Built to Throw

The Fenix TK11R uses the SFT40 to put out 1,600 lumens with a 420-meter beam distance in a compact, 4.14-ounce tactical body — a clear throw-first design, useful when you need to identify something well ahead of you rather than just light up what's close.

Fenix PD35 V3.0 — SFT40, Balanced EDC Throw

The Fenix PD35 V3.0 also uses an SFT40, delivering 1,700 lumens, 31,900 candela, and a 357-meter beam distance through a de-convex lens and small-caliber reflector — proof that an SFT40 doesn't require a huge head to be effective, just a reflector built around it.

Fenix E18R V2 — SST40, Built for Close-Range EDC

The Fenix E18R V2 uses the SST40 instead, at 1,200 lumens and a 146-meter beam distance in a pocket-sized 2.64-inch body. That's a much shorter beam than the TK11R's, but the E18R V2 isn't trying to compete on distance — it's built for close-range, everyday tasks where a wider, more even beam is more useful than a tight hotspot.

Which One Should You Care About?

Most buyers aren't choosing a bare LED — they're choosing a flashlight, and the emitter just explains why it behaves the way it does. As a rule of thumb: if you need to identify something well ahead of you — property lines, a trail marker, movement at distance — look for an SFT40 in a light with a reasonably sized head, since that's where its advantage actually shows up. If you're mostly using a light at arm's length or across a room — repairs, camping tasks, finding something in a bag — an SST40's wider, more even beam is usually the better fit, and you're not giving up much by skipping the extra throw.

Either way, check the actual beam distance and candela figure on the specific flashlight, not just which LED it uses — the same emitter can perform differently depending on the reflector it's paired with.

Frequently Asked Questions

Q: Is the SFT40 just a better LED than the SST40?
A: Not exactly — it's built for a different job. The SFT40 concentrates light for throw; the SST40 spreads it for a wider, more even beam. Which one is "better" depends on whether you need distance or close-range coverage.

Q: How much farther does an SFT40 actually throw than an SST40?
A: It varies by flashlight. In controlled testing of the same flashlight body and reflector with both LED options, the SFT40 measured about 50% higher candela than the SST40 — a real gain, though testers noted it's most worthwhile in a light with a larger head to take advantage of it.

Q: Why does Fenix use SFT40 in some flashlights and SST40 in others?
A: It comes down to the flashlight's purpose. Throw-oriented lights like the TK11R and PD35 V3.0 use the SFT40 to maximize beam distance, while compact EDC lights like the E18R V2 use the SST40 for a broader, more practical close-range beam.

Find Your Flashlight

Browse Fenix's full flashlight collection to compare throw-focused and everyday-carry options side by side.