Think in Systems
A headlamp is only one part of night strategy. You need light on the course, power through the night, and enough comfort that the lamp does not become another problem at 3 AM.
Product examples live in our headlamp guide. This page is about the race plan.
Battery Math
Battery capacity and usable running time are different measurements. Petzl lists the NAO RL battery at 3.2 Ah × 3.7 V = 11.84 Wh. Dividing nominal energy by an advertised runtime does not establish measured power draw or constant light output: usable energy, reserve modes and dimming curves also matter.
Under ANSI/PLATO FL 1, runtime can extend until output falls to 10% of its initial value. Read the mode and output curve, then test how long the lamp provides enough light for your terrain. BioLite makes the distinction explicit: its 800 Pro lasts 4 hours at medium in Constant Mode, versus 8.5 hours in its dimming Regulated Mode.
| Lamp and mode | Listed output | Runtime | Interpretation |
|---|---|---|---|
| Petzl NAO RL — STANDARD LIGHTING, Standard level | 250 lm | 5 h | ANSI-rated; verify usable output over time |
| Petzl NAO RL — STANDARD LIGHTING, Max Power | 900 lm | 2 h | ANSI-rated; higher output shortens runtime |
| BioLite 800 Pro — Medium, Constant | 250 lm | 4 h | Constant Mode |
| BioLite 800 Pro — Medium, Regulated | 250 lm initially | 8.5 h | Dims over time |
| BioLite 800 Pro — High, Constant | 500 lm | 2 h | Constant Mode |
| BioLite 800 Pro — High, Regulated | 500 lm initially | 7 h | Dims over time |
A Worked 24-Hour Night Plan
Consider a crewed one-mile loop with ten hours of darkness, 20:00 to 06:00. For this arithmetic example, assume you have established five hours of adequate light per charge in the mode and conditions you will use. That is an assumed test result, not a promise that an advertised five-hour runtime holds its initial output.
| Step | Calculation |
|---|---|
| Base requirement | 10 h ÷ 5 usable h per charge = 2 charges |
| Example planning margin | 2 × 1.5 = 3 fully charged batteries in total |
| Loadout | One installed battery, two spares, plus an independent backup light |
If testing gives only four usable hours, the same calculation becomes 10 ÷ 4 × 1.5 = 3.75, rounded up to four batteries. Do not budget hours at a very low setting unless that setting actually provides safe visibility; nearby runners are not a dependable lighting system.
The Margin Rule
The 1.5× margin is our planning example, not a manufacturer guarantee or an event rule. Cold, older cells, weather and higher output can require a larger reserve. Follow mandatory-kit rules first and carry an independent light that works if the primary lamp itself fails.
Plan swaps at the crew table before the tested usable runtime ends. For a sealed battery, use a second lamp or a manufacturer-supported, tested external-power setup; a power bank alone does not solve a broken lamp or connector. Rehearse swaps and keep dry charged spares clearly separate from used batteries.
Budget each darkness period separately in a 48-hour or six-day race, including charging time and access. For a backyard, check charge state before each dark yard and plan resupply for an event that can outlast your initial goal.
Testing
Test the lamp on the settings and terrain you expect to use, not only the brightest setting on the product page. Manufacturer runtime can be measured under conditions that differ from your weather and use.
- Test long enough to observe output changes and pressure or bounce.
- Wear the same hat, buff, or glasses you expect to use.
- Check bounce, forehead pressure, and whether buttons work with gloves.
- Rehearse charging or battery swaps in a safe, well-lit place.
- Compare settings without reducing light below what safe footing requires.
Backup Plan
If a light fails, stop at a safe place before troubleshooting or changing batteries. Do not continue over technical or unlit ground with inadequate visibility. Any required backup must stay with you as the rules specify; otherwise, decide where to carry it from the distance to the next staffed aid point or safe exit, not merely the distance to crew.
Add lights, cables, and batteries to the gear checklist generator before race week.
Sources
- Petzl — official explanation of brightness, beam shape, and burn-time tradeoffs.
- Petzl — ANSI/PLATO FL 1 lighting-performance measurements.
- Eiger Ultra Trail by UTMB — official mandatory-equipment example; check your own event's current rules.
- Petzl — NAO RL product specifications: 145 g, 1,500 lm maximum, 3200 mAh / 3.7 V (11.84 Wh) battery, and standard-lighting runtimes of 10 lm for 80 h, 250 lm for 5 h, and 900 lm for 2 h (read 23 October 2026).
- BioLite — HeadLamp 800 Pro product specifications: 150 g, 3000 mAh battery, 5 lm for 150 h, 250 lm for 4 h and 500 lm for 2 h in Constant Mode; 8.5 h and 7 h respectively in dimming Regulated Mode; and an 800 lm burst lasting 30 seconds (read 23 October 2026).
The charge budget is illustrative arithmetic from an assumed usable runtime. Test your own lamp and battery; advertised capacity and ANSI runtime alone do not establish a safe night-running duration.
Frequently Asked Questions
How many headlamps do you need for a 24-hour race?
Carry every light and power source required by the current race rules. Where the rules do not specify a number, choose redundancy from the hours of darkness, terrain, remoteness, aid access, weather, and the consequence of a failure; test the complete system before race day.
How many lumens do you need for an ultra?
150–300 lumens of sustained output for a lit or smooth loop course, and 400–600 lumens for technical trail. Sustained output matters more than the peak figure on the box, so check how long the lamp holds your setting, and follow any event minimum.
Should you use reactive lighting?
Reactive lighting can save battery and reduce fiddling, but test it first. Some runners prefer predictable manual settings in fog, rain, groups, or reflective environments.