Best Headlamps for Night Running and 100-Milers: Lumens, Runtime and the Battery Plan

For a 100-miler, run two lamps, and buy them for their runtime at 100 to 200 lumens rather than for the number on the box. The pairing that covers most runners: a primary with a swappable or hybrid battery, such as the Petzl Actik Core (625 lumens on its rechargeable CORE pack, 88 grams, and it falls back to three AAAs when the pack dies), plus an ultralight backup that lives in the vest all night, such as the Nitecore NU25 400 UL (400 lumens, 47 grams, USB-C, IP66). The battery plan matters more than either lamp: a charged spare pack in the night-transition drop bag, lithium AAAs as the emergency layer, and a small power bank to top up the backup during a longer stop.

Lumens versus runtime: the honest math

Every headlamp box leads with maximum lumens, and every maximum-lumen figure is a two-hour number. Petzl lists the Actik Core at 625 lumens for 2 hours on the CORE battery, 100 lumens for 7 hours, and 7 lumens for 100 hours. Nitecore's manual lists the NU25 UL at 400 lumens for about 2 hours 40 minutes, 200 lumens for about 4 hours 40 minutes, 60 lumens for about 10 hours 25 minutes and 6 lumens for 45 hours. Neither lamp will run its top mode for a night, and neither is meant to.

Now put that against the night itself. An autumn 100-miler with sunset around 7 p.m. and sunrise around 6:30 a.m. is about 11.5 hours of darkness. A summer race is closer to 8 or 9. A worked plan for the Actik Core over an 11.5-hour night:

• Standard mode (100 lumens) on climbs and smooth trail, where you are moving slowly and the ground is predictable: call it 8 of the 11.5 hours.
• Max mode for technical descents, junction-finding and the moments a light matters: call it 1.5 hours.
• Standard mode draws roughly 1/7 of the pack per hour; max mode roughly 1/2 per hour. Eight hours at standard is more than a full pack on its own, so one battery swap is not optional, it is the plan.
• That swap happens where the drop bag is: a second charged CORE pack in the night-transition bag, or three lithium AAAs, which Petzl rates at 10 hours in standard mode (max drops to 450 lumens on AAAs).

For the NU25 UL as a backup the arithmetic is easier. In low mode (60 lumens) it covers a full night by itself, and a 5,000 mAh power bank refills its roughly 650 to 700 mAh cell several times over. Its job is to be there, weigh nothing, and get you to the next aid station if the primary fails.

Two other truths about the headline number. First, a regulated lamp holds its output and then drops to a reserve mode; an unregulated one dims steadily from the moment you switch it on, so a 400-lumen unregulated lamp is a 150-lumen lamp two hours later. Petzl and Nitecore both publish stepped runtime tables, which is a good sign. Second, more lumens is not always more sight. In fog, dust or fine rain, a bright spot beam lights the air in front of your face; a lower flood setting often shows more trail.

Beam pattern: the spec that decides whether you can see

Lumens describe how much light leaves the lamp. Beam pattern describes where it lands. Trail running wants a mixed beam: a flood component to light your feet and the trail edges, and a spot component to reach the next twenty meters and pick out course markers. The Actik Core uses a wide mixed beam with a focused center, which is why it is a default recommendation for night trail. The NU25 UL offers separate spot and flood emitters that run alone or together, so you can run flood-only on a smooth climb to save the battery and add the spot for a descent.

Both lamps have a red mode, which is worth using at aid stations and around sleeping crews, and for reading a pit card without wrecking your night vision. A waist lamp is the other tool worth knowing about: mounted low, it throws shadows that show the texture of rocks and roots, and many 100-mile runners pair a modest headlamp with a waist light for exactly that reason.

Reactive lighting: what it is and whether you need it

Petzl's Reactive Lighting uses a sensor that reads the light bouncing back at the lamp and adjusts output automatically: dimmer when you look at your hands or a map, brighter when you look down a dark trail. It is on the Swift RL (900 lumens) and the Nao RL (1,500 lumens), not on the Actik Core. The benefits are real: battery lasts longer because the lamp is rarely at full power, and you stop fiddling with buttons. The costs are also real: the lamp dims when it sees a reflective bib or a wet rock, some runners find the fluctuation distracting on technical ground, and the price roughly doubles.

For a first 100-miler, predictability tends to win. A three-mode manual lamp behaves the same at 3 a.m. as it did on the couch, and the battery math above works because the draw is known. Reactive lighting suits runners who race often at night and hate managing modes. It is a preference, not an upgrade everyone needs.

Battery strategy at aid stations

There are three battery architectures, and your drop-bag plan follows from which one you carry.

• Swappable proprietary pack (Actik Core with a CORE pack): buy a second pack, charge both, put the spare in the night bag with the date on a strip of tape. The swap takes thirty seconds sitting down. Charge over USB-C from any power bank if the stop is long enough.
• Hybrid AAA fallback (Actik Core again): three lithium AAAs in a small zip bag weigh about 45 grams and satisfy most mandatory-kit "spare batteries" rules. Lithium cells hold their voltage in the cold far better than alkalines, which is why alkalines have no place in a night bag.
• Sealed USB-C rechargeable (NU25 UL): no swap possible, so the plan is a small power bank and the correct cable. Top it up while you eat at a longer stop, and run it in low or ultralow the rest of the time.

Cold is the variable people forget. Battery capacity drops as temperature falls, and the coldest hours are the last ones before dawn. Keep the spare pack and the power bank inside a jacket pocket rather than an outer vest pocket, and swap earlier than the runtime table says if the night is near freezing.

The concrete plan for a 7 p.m. to 6:30 a.m. night: pick up both lamps and the spare pack at the night-transition bag; start the primary in standard mode; run max only on descents and at junctions; swap the pack at the deep-night station around midnight to 1 a.m.; keep the NU25 UL on the vest strap in ultralow as a secondary from the start of darkness; recharge it at the sunrise bag if the race allows a power bank. The drop-bag guide covers where each item sits.

The two picks, and what each is for

Spec (manufacturer-listed)	Petzl Actik Core	Nitecore NU25 400 UL
Max output	625 lm (CORE pack); 450 lm on AAAs	400 lm
Weight with battery	88 g	47 g with band
Battery	1,250 mAh CORE, USB-C; or 3 x AAA	built-in 650 to 700 mAh, USB-C
Runtime at max	2 h	about 2 h 40 min
Runtime, mid	7 h at 100 lm	about 4 h 40 min at 200 lm
Runtime, low	100 h at 7 lm	about 10 h at 60 lm; 45 h at 6 lm
Beam	wide mixed with focused center	spot + flood, separate or together
Red light	yes	yes
Weather rating	IPX4	IP66
Typical price	around $90	under $40

Petzl Actik Core: the primary. The hybrid battery design is the reason to buy it for ultras specifically; the same lamp that runs a rechargeable pack all night will run gas-station AAAs if everything else goes wrong. Its weaknesses are real but minor: the IPX4 rating means it shrugs off rain but should not be submerged, the band is a standard elastic, and it has no reactive mode.

Nitecore NU25 400 UL: the backup that becomes a primary on runnable trail. Forty-seven grams is light enough to forget, the thin band stays put, IP66 handles heavy rain, and the separate spot and flood emitters give more control than the price suggests. The limitation is the sealed cell: no swap, so its runtime is your power bank's runtime.

If you want more light than either, the options run in a fairly predictable ladder: the Petzl Swift RL for reactive lighting around 900 lumens, the Petzl Nao RL with a rear-mounted battery for balance at 1,500 lumens, and lamps built around a removable 18650 cell such as the Fenix HM65R-T, which trade weight for the ability to carry cheap spare cells. All are heavier and cost more; none change the battery-plan logic above.

Mandatory kit and race rules

Most mountain 100-milers and many 100Ks require two headlamps with spare batteries in the mandatory kit, and gear checks at aid stations do happen. The two-lamp system above satisfies the rule without extra weight. Carry both from the moment you pick them up rather than leaving the backup in a later bag, because the rule is about the section between stations, and so is the risk.

Mistakes to avoid

• Starting the night at max because it feels safer. It feels safer for two hours.
• Alkaline AAAs in a cold night bag.
• A power bank with the wrong cable, or a cable that only charges the phone.
• Not learning the button sequence in the dark before the race. Every lamp has a mode you do not want that is one press away.
• One lamp, one battery, one plan.
• Buying on lumens and discovering the beam is a narrow spot that turns singletrack into a tunnel.

Buy for the 100-lumen runtime, plan the swap, and treat the box's big number as the setting you use for descents.