Skip to content
Tom's HikingTom’s Hiking

Lighting and electronics

Lumens

Also called lumen output, lm

What are lumens?

Lumens measure the total light a headlamp emits in all directions. It's the headline number on every box and it says nothing about where that light goes, so a 400 lumen lamp with a bad beam can be less useful than a 200 lumen one with a good one.

Lumens at a glance

Camp and easy trail
Around 100 lm
Night hiking
200 to 350 lm
Running technical trail
400 lm and up

What a lumen actually measures

A lumen is a unit of total luminous flux, meaning all the light leaving the lamp regardless of direction. Two lamps rated at 300 lumens can put wildly different amounts of light on the trail thirty feet ahead, because one might spread it in a wide wash and the other concentrate it into a spot.

Why the headline number flatters

The number is also quoted at its most flattering. Brands publish maximum output, which most lamps hold for a couple of minutes before thermal regulation steps it down. The number you should care about is the output on the setting you'll actually run for hours, which is usually a third to a half of the headline figure and much harder to find on the packaging.

How many lumens you need

As rough guidance: 100 lumens is enough for camp chores and a well-marked trail at walking pace, 200 to 350 covers most night hiking, and 400 and up starts to matter when you're running technical ground and need to read it at speed. Past about 600 lumens on trail you're mostly buying battery drain and glare off fog.

What this means when you're choosing

  • Regulated output, without which the lumen figure lasts minutes
  • Beam distance alongside it, which says where the light goes
  • Burn time quoted at a brightness you would actually use

The common mistake

Buying on maximum lumens

Maximum output usually lasts minutes before the lamp steps down to protect itself. Compare lamps on their regulated output and burn time at a setting you'd genuinely use all night.

Common questions

How many lumens do I need for night hiking?

200 to 350 lumens covers walking pace on most trail. Running technical ground is where 400 and up earns its keep, and camp tasks need far less than people buy for.

Are more lumens always better?

No. Beyond what the terrain needs, extra output mostly burns battery, and in fog or rain a very bright wide beam reflects back at you and makes seeing harder rather than easier.

Where this is defined

Where this comes up

Guides on Tom's Hiking where lumens changes which product is right for you.

More in lighting and electronics

Beam distance

Beam distance is how far a headlamp usefully projects light, quoted in meters. The industry standard measures it to the point where illumination falls to 0.25 lux, roughly the brightness of a full moon, which is dimmer than most people picture.

Flood vs spot beam

A flood beam spreads light wide and close for camp tasks and slow ground. A spot beam concentrates it into a narrow cone that reaches further, for seeing ahead at speed. Most trail headlamps mix both, and the mix matters more than the lumen count.

Regulated output

A regulated headlamp holds a steady brightness as its battery drains, then drops off sharply near the end. An unregulated one fades continuously from the moment you switch it on, so it's dim long before the battery is actually empty.

Reactive lighting

Reactive lighting uses a sensor to measure reflected light and adjusts brightness automatically, dimming when you look at a map and brightening when you look down the trail. It extends battery life and can feel unpredictable at speed.

Red light mode

Red light mode is a dim red setting on a headlamp that lets you see nearby things without spoiling your night vision. Your eyes take 20 to 40 minutes to adapt fully to the dark, and white light undoes that in seconds, while dim red light barely disturbs it.

IP rating

An IP rating states how well a device resists solids and water, under the IEC 60529 standard. The first digit covers dust and the second water, so IPX4 is splash resistant, IPX7 survives brief submersion, and IP67 does both.

Watt-hours (Wh)

Watt-hours measure how much energy a battery stores: voltage multiplied by capacity in amp-hours. Unlike mAh, which is quoted at the cell's own voltage, watt-hours let you compare any two batteries fairly, and they are the unit airlines use to set carry-on limits.

GPX file

A GPX file is the standard open format for storing GPS routes, tracks and waypoints as plain text. It's what you download from a trail site and load onto a watch or phone, and almost every mapping app and GPS device reads it.

Breadcrumb navigation

Breadcrumb navigation draws your loaded route as a line on a blank screen with an arrow for your position, without any underlying map. It tells you whether you're on the route, and nothing about what's around you.

ABC sensor

ABC stands for altimeter, barometer and compass, the three sensors in an outdoor watch. The altimeter and barometer are the same pressure sensor read two ways, and the compass is a magnetometer that gives you a heading when you're standing still.

Exit pupil

Exit pupil is the width of the beam of light a binocular sends to your eye, found by dividing the objective lens size by the magnification. An 8x25 has a 3.1mm exit pupil and an 8x32 has 4mm; the bigger number looks brighter in dim light.

Eye relief

Eye relief is how far behind a binocular's eyepiece your eye can sit and still see the whole field of view, measured in millimeters. Glasses hold your eye farther back, so hikers who wear them need about 15mm or more to avoid a view ringed in black.

ED glass

ED glass, short for extra-low dispersion, is lens glass that bends red, green and blue light by nearly the same amount. In binoculars it cuts the purple and green fringes around dark edges against a bright sky, so the image looks sharper and truer in color.

By Tom · Last reviewed . Back to the glossary