Guides
ANSI FL1 Explained
The standard behind the numbers on the box, what it actually specifies, where it falls short, and what a brand is telling you by never mentioning it.
By Scooter M. · Published September 2, 2026
What the standard measures
| Measurement | How the standard defines it | Reported in |
|---|---|---|
| Light output | Total quantity of emitted light energy | Lumens |
| Peak beam intensity | Value at the brightest part of the beam | Candela |
| Beam distance | Distance at which the beam falls to 0.25 lux | Meters |
| Run time | From the value 30 seconds after switch-on until output drops to 10% of it | Hours |
| Impact resistance | Drops onto concrete at a stated height, with batteries fitted | Meters |
| Water resistance | Splashing, temporary immersion or continuous immersion | IPX4 / IPX7 / IPX8 |
ANSI FL 1 is the industry standard that defines how flashlight performance is measured: light output in lumens, peak beam intensity in candela, beam distance to the point where the beam falls to 0.25 lux, runtime from the 30-second output value until it drops to 10 percent of that value, impact resistance as a tested drop height, and water resistance as an IPX rating.
The two definitions that change how you read a spec sheet
Runtime starts at 30 seconds, not at zero
The standard defines the initial output value as the reading 30 seconds after switch-on with fresh batteries. That single detail is why turbo modes are not usually quoted with runtimes: a light that steps down at forty seconds has already left the mode by the time the standard's clock has properly started.
Runtime ends at 10 percent, which is the loophole
Run time is measured until output falls to 10 percent of that 30-second value. Ten percent. A light quoted at 1,000 lumens with a four-hour runtime may have spent most of those four hours at a fraction of a thousand lumens and still comply completely.
NitecoreLights names this as the standard's biggest limitation in its own published guide: capturing how a light really behaves requires a runtime graph, which FL 1 does not require. Its illustration is that two lights with similar runtime ratings can behave completely differently — one holding steady within 10 percent of its initial brightness, the other declining continuously from the start.
What a missing FL1 citation tells you
Very few brands state conformity explicitly. Petzl does: it publishes the ACTIK CORE's 625-lumen figure as ANSI/PLATO FL 1. Most of the manufacturers we cite publish lumen, runtime and beam-distance figures in FL 1's shape without naming the standard.
That is not automatically suspicious — using the conventions without citing the document is common. What is informative is the pattern: brands that publish a complete set of figures in FL 1's format are behaving like brands that measured them. Brands that publish a single lumen number with no runtime, no beam distance and no water rating are not measuring to any standard you can check.
Water resistance under the standard
The standard uses IPX ratings, and NitecoreLights sets out the three that appear on flashlights: IPX4 as water-resistant against splashing from all directions, IPX7 as waterproof to temporary submersion at one meter for thirty minutes, and IPX8 as submersible at a specified depth for a longer period.
Those definitions are why a missing water rating is worth noticing. IPX4 and IPX8 are enormously different promises, and 'water resistant' with no figure attached sits outside the standard entirely. Our guide to IP ratings goes through the whole scale.
How this site uses the standard
Every lumen figure in our tables is the manufacturer's published maximum, and we note where a brand explicitly states ANSI/PLATO FL 1 conformity rather than assuming it. Every runtime we quote is the manufacturer's, at the mode they attached it to. We do not measure anything ourselves and we do not present anyone else's measurement as ours.
Units we claim to have tested: 0
Every publisher in this category says they tested twenty flashlights. We have not tested any, and we say so. What we do instead: compile the manufacturer's own published ANSI FL1 figures, pull the price the light is selling for right now, and divide one by the other. Every number on this page is one you can check yourself in about two minutes.
Common questions
What is the ANSI FL1 standard?
It is the industry standard defining how flashlight performance is measured and reported: light output in lumens, peak beam intensity in candela, beam distance to the 0.25 lux point, runtime from the 30-second output value until output falls to 10 percent of it, impact resistance as a tested drop height onto concrete, and water resistance as an IPX rating.
Why does ANSI FL1 measure runtime to 10 percent?
Because it needs a defined end point, and 10 percent of the initial value is the one the standard chose. The consequence is a real limitation: a light can be quoted with a long runtime while spending most of it far below its headline output. NitecoreLights names this as the standard's biggest weakness and notes that showing real behavior requires a runtime graph, which FL 1 does not require.
Do all flashlights follow ANSI FL1?
No. It is a voluntary standard, and while most established manufacturers publish figures in its shape, few state conformity outright — Petzl is one that does, citing ANSI/PLATO FL 1 for the ACTIK CORE's 625 lumens. A brand publishing a lone lumen figure with no runtime, beam distance or water rating is not reporting against any standard you can check.
Sources
- Streamlight, ANSI Information — definitions of light output, beam distance, run time, impact and water resistance under the FL1 standard, read 2026-09-01
- NitecoreLights, ANSI / NEMA FL-1 Guide — FL1 definitions plus a published account of the standard's runtime limitation, read 2026-09-01
- Petzl published product specifications — ANSI/PLATO FL 1 conformity stated by the manufacturer, read 2026-09-01
- Lumen & Ledger method — how every figure on this page is derived
Who writes this
Scooter M. — I am an enthusiast who is genuinely into this. I read the manuals, compile the published specs, and do the math. No lab coat, no test bench, no drawer of free samples. What I can tell you is exactly what a light claims on paper, exactly what it costs right now, and what those two numbers mean when you divide one by the other.
Read next
The 10,000-lumen problem
Why the biggest number on the box is the one you can use for the shortest time.
Lumens vs candela
One measures how much light there is. The other measures how far it goes.
IP and IPX ratings explained
What IPX4, IPX7 and IP68 mean, and why a missing rating is information too.
How many lumens do you actually need?
A table by use case. Most people need far fewer than the box is selling them.
Best high-lumen rechargeable flashlights
High output judged on sustained performance rather than a thirty-second peak.
The Ledger
Every light we cover in one ranked table, sorted by lumens per dollar.