In my last Light Education post, we talked about how to read a spec sheet. The spec sheet tells you where a light starts. An output graph tells you the rest of the story.
At Low Light Defense, we publish output graphs for the lights we test. They can look intimidating at first, but once you know what to look for, you can size up a light in a few seconds.
The basics are simple. The horizontal axis is time, measured from the moment the light turns on. The vertical axis is output, usually in lumens, the total amount of light coming from the light. We measure that output with an integrating sphere. Each line is one light, so you can watch how its output changes over the entire run.
The First Few Minutes
For a defensive light, this is the part of the graph that matters most. Here’s what to look for:
- The peak. Most lights start at their highest output the instant they turn on.
- The 30-second mark. This is where manufacturers measure their lumen rating under the ANSI standard. In our testing, I also score lights at 30 seconds to reduce the chance a manufacturer is gaming the numbers.
- The step-down. Many high-output lights heat up and drop their output to protect themselves. Watch how far the line falls, and how soon.
Some lights step down before the 30-second mark even arrives. In our 2026 handheld test, the NiteCore EDC31 samples measured roughly 32,000 to 38,000 candela at turn-on, but only about 17,000 to 20,000 candela at 30 seconds. That’s about half its claim, just 30 seconds in.
A quick step-down isn’t automatically a deal breaker. As I’ve said before, I’d like to see about five minutes of good, strong output from a defensive light. The question is where the line settles after the drop.
The Long Run
After the first few minutes, look at the shape of the line.
A flat line means the light is regulated. Its electronics hold output steady as the battery drains. That’s what you want, because the light behaves the same way at minute 30 as it did at minute 5.
A sloping line means output is fading along with the battery. The light gets gradually dimmer the longer you use it.
Then look at the end of the line. Regulated lights often hold steady until the battery is nearly empty, then drop off sharply. Often the line falls to zero because of low voltage protection, which shuts the light off before a rechargeable cell drains below its minimum voltage of around 2.5V. That protects your battery, but it can leave you in the dark with little warning. A light that tapers off gives you more notice that it’s time to swap or charge the battery.
These differences add up. In our 2026 handheld test, 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. Two lights can look similar on a spec sheet and be worlds apart on the graph.
Comparing Lights and Samples
Our graphs usually show several lights at once, and that’s where they become really useful. A light that looks impressive by itself might fall behind the pack once you put it next to its competitors.
We also test multiple samples of each light, typically three. If a light’s lines track closely together, the manufacturer is building consistent lights, and the one you buy should perform like the ones we tested. If the lines are scattered, you could get a great one or you could get a dud.
In our 2026 handheld test, the Streamlight MegaStream samples were extremely consistent, while the Cloud Defensive samples were the least consistent, with jagged output curves.
The Bottom Line
When you look at an output graph for a defensive light, ask yourself four questions:
| Question | What You Want to See |
|---|---|
| How high does it start? | Strong output at turn-on and at 30 seconds |
| How far does it drop, and how soon? | A modest step-down, after providing five to ten minutes of strong output |
| Where does it settle? | A flat, regulated line at a useful level |
| Do the samples agree? | Lines that track closely together |
A spec sheet gives you a single snapshot. An output graph shows you how a light will actually perform when you need it. Some manufacturers are now providing output graphs, but this is still rare. Your best source is an independent test house. Next time you’re shopping for a light, check out the data at Low Light Defense before you buy.
