Headlamp Lumens and Runtime: How to Read the Box Before You Buy

What the FL1 standard actually measures

A number is only as good as the method behind it. For portable lights, the benchmark is a US standard, ANSI/PLATO FL1, which spells out how to take six measurements, from light output to water resistance [1]. It’s voluntary. But a brand that puts the FL1 icon on its packaging has to follow those methods for every number on the box, not just the one that makes it look best [1].

Runtime, the number that misleads the most

On paper, 40 hours of runtime means 40 hours of light. The standard says otherwise: the clock starts 30 seconds after you switch the lamp on and stops when output drops to 10% of its initial value [1, 2]. That cutoff isn’t arbitrary: according to the standard, it’s the level at which people typically replace their batteries [1].

From there, it all comes down to the shape of the curve. An unregulated headlamp feeds its LED directly: it’s very bright for the first few minutes, then dimmer and dimmer as the hours go by, and the higher its starting output, the faster that output fades [3]. A regulated headlamp, on the other hand, holds steady output for a set period, which is the runtime you can actually use, then often drops into reserve lighting [3]. So two headlamps can list the same runtime and still give you a very different night.

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Petzl offers a reality check: 100 lumens for 50 hours would take the equivalent of 75 AAA batteries, or 2.4 pounds (1.1 kg) on your head [3]. When a spec sheet pairs a very high output with a very long runtime, the two numbers often come from different modes: the output from max mode, the runtime from the lowest mode [3]. You can’t have both at once.

Lumens, candela, beam distance: three numbers, three questions

The lumen count covers all the light coming out of the lamp. The candela figure measures intensity at the core of the beam, where it’s strongest. Beam distance, finally, is how far out the light drops to 0.25 lux, roughly the light of a full moon on a clear night in an open field [1, 2]. Two headlamps with the same output can reach very different distances: beam distance depends on output, but even more on the shape of the beam [2]. A wide beam lights up camp; a tight one reaches far down the trail.

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Let’s run the numbers: 1,000 candela gives a beam distance of about 207 feet (63 m), and 2,500 candela gives 328 feet (100 m). To double the distance, you need four times the intensity: the inverse square law, which the standard is built on, doesn’t cut anyone any slack. And since FL1 reports beam distance in meters, multiply an FL1 rating by 3.28 to get feet [1].

Water and impact resistance: what IPX4, IPX7, and IPX8 mean

• IPX4: splashing water from any direction must not damage it. A downpour, yes; a dunk in a creek, no.
• IPX7: temporary immersion, under standardized conditions (the FL1 test is done under 3.3 feet, or 1 m, of water).
• IPX8: prolonged immersion, under conditions tougher than for IPX7, which the manufacturer has to specify [1].

For impact, the standard drops the lamp six times onto concrete, from at least 3.3 feet (1 m), and it has to come through with no cracks and no malfunction [1]. A higher drop rating on the package means the lamp passed the same tests from that height.

Batteries, rechargeables, and the cold

The energy on board drives everything else: for the same energy reserve, more light means less runtime, and you’ll never get a high output and a record runtime at the same time [3]. In deep cold, battery type matters too. According to Petzl, lithium batteries (the disposable kind) perform better than alkaline and NiMH batteries at extreme temperatures, and work from -4 to 122 °F (-20 to +50 °C) [4]. Before you load them into a headlamp, check the manual to make sure it takes them.

Comparing two headlamps in five minutes

1. Look for the FL1 icon: without it, there’s no telling how the numbers were measured.
2. Compare runtimes in the mode you’ll actually use, rather than in the lowest mode.
3. Check the light-output chart if there is one: steady output beats a peak at switch-on.
4. Match beam distance to the job: camp calls for a wide beam, night hiking for one that reaches out.
5. Check the water rating and, if you’re heading into the cold, which batteries the lamp takes.

A number without a unit is a promise without a contract; a number without a method isn’t much better. The FL1 standard supplies the method: reading the fine print is up to you.

Julien de Jurquet

Vans, RVs, biking and calculators

Julien de Jurquet writes for Outfarer about camper vans, RVs, biking, and calculators. He reads manuals cover to cover and never lets a number slide without its unit, so your choices rest on math, not promises.

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