In my last Light Education post, we talked about the difference between lumens and candela. But knowing what the numbers mean is only half the battle. You also need to know how those numbers are measured, because a spec sheet can be technically accurate and still mislead you.
One thing I’ve learned over the years is that you cannot trust a manufacturer’s claim for light output. That’s why we bought our own lab equipment and test our lights in-house. Our in-house testing eliminates the issue of using different equipment, different methodologies, or outright fudging the numbers.
Most reputable manufacturers rate their lights using the ANSI/PLATO FL1 standard. That’s a good thing, since it means everyone measures the same way. But the standard has a few quirks you need to understand. Let’s walk through them.
Lumens: The 30-Second Number
Under FL1, lumens are measured 30 seconds after you turn the light on. That’s it. The standard doesn’t require the light to hold that output.
Many high-output lights get hot quickly and step down to protect themselves. So a light advertised at 1,000 lumens might deliver that for a minute or two, then drop to a fraction of it.
For a defensive light, the first few minutes matter most, so a short step-down isn’t always a deal breaker. As I’ve said before, I’d like to see about five minutes of good, strong output. The point is to know what you’re actually getting. The good news is that the 2025 revision of FL1 adds optional reporting of sustained output, so watch for manufacturers who choose to publish it.
Sometimes Light Output QuicklyDrops
Candela and Beam Distance: Same Number, Different Package
Here’s something most people don’t realize: beam distance isn’t a separate measurement. It’s calculated directly from candela.
FL1 defines beam distance as the point where the light falls to 0.25 lux, which is roughly the brightness of a full moon. The math works out to two times the square root of the candela. So a light with 20,000 candela, my personal minimum for a defensive light, is rated at about 283 meters. A 100,000 candela light is rated at about 632 meters.
Think about what that means. At the rated beam distance, your target is lit about as well as by moonlight. You might see that something is there, but you’re not going to positively identify a person or see what’s in their hands. Your useful identification distance is a fraction of the advertised number.
Since beam distance is just candela in another form, I’d skip it entirely and compare candela.
Runtime: The 10% Rule
FL1 runtime is measured from that 30-second mark until the output drops to 10% of its starting value. On a 1,000 lumen light, the runtime clock keeps ticking until the light is down to 100 lumens.
So a light rated for 90 minutes might spend most of that time at a small fraction of its advertised output. Two lights with identical runtime ratings can behave very differently in between.
That’s why we don’t rely on the runtime spec. In our testing, we record full output graphs that track a light’s output over the entire run, often two hours or more. In our 2026 handheld test, for example, some lights were down to around 14 lumens at the two-hour point, while the Fenix PD36R Pro was still putting out around 650 lumens. You’d never know that from the runtime spec alone.
Some Lights Provide High Output Hours In
Durability Ratings: A Starting Point
Spec sheets also list an impact rating, which is the height the light survived when dropped onto concrete, and a water rating. IPX4 means splash resistant, IPX7 means temporary immersion to 1 meter, and IPX8 means deeper immersion, to a depth the manufacturer specifies.
Treat these as a minimum, not a guarantee. In our 2026 handheld test, the Olight and Cloud Defensive lights both had water intrusion in our fish tank, which isn’t even a meter deep. In the 2-meter tank, the Olight and Nitecore took on enough water to start turning on and off by themselves.
The Bottom Line
Here’s a quick cheat sheet for the next time you read a spec sheet:
| Spec | What It Actually Means | What to Watch For |
|---|---|---|
| Lumens | Output 30 seconds after turn-on | Step-down after a minute or two |
| Candela | Intensity at the center of the beam | As with lumens, candela steps down over time |
| Beam distance | Where the light falls to moonlight levels | Don’t expect that you can ID someone at the shown distance |
| Runtime | Time until output drops to 10% | Much of that time may be at low output |
| Impact and water | Minimum survival ratings | Real-world durability varies |
The spec sheet tells you where a light starts. To know how it actually performs, you need to see the output over time. That’s why we publish output graphs on Low Light Defense. In a future Light Education post, I’ll show you how to read one.
