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Lighting and electronics

Regulated output

Also called constant output, regulated brightness

What is 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.

Regulated output at a glance

Regulated
Constant, then a sharp drop
Unregulated
Fades from the first minute
Read
Burn time and brightness together

Why an unregulated lamp fades

A raw LED gets dimmer as battery voltage falls. Left alone, a headlamp starts bright and fades continuously, so after two hours you're running on noticeably less light than you started with and you've slowly adapted to it without noticing.

What regulation does

Regulation puts a circuit between the battery and the emitter that maintains constant current until the battery can no longer supply it. You get the same brightness for most of the burn, and then a fairly abrupt drop to a reserve level. Most good lamps warn you before that happens, and some step down in stages rather than all at once.

Reading burn time against it

This is what makes burn time figures comparable, so read them together. An unregulated lamp claiming twelve hours may be quoting the point at which it produces almost nothing. A regulated lamp claiming six hours is usually promising six hours of the brightness you selected, which is a completely different claim. The catch is the cliff: when a regulated lamp goes, it goes quickly, so carry a spare battery or a second light on a long night.

What this means when you're choosing

  • A stated regulated runtime rather than a bare burn time
  • A reserve or low-power warning, since regulated lamps drop off suddenly
  • Whether the quoted time is at high or at a mode you would use

The common mistake

Comparing burn times across regulated and unregulated lamps

An unregulated lamp claiming twelve hours is emitting almost nothing for the last several. A regulated one claiming six holds useful light for six and then goes. The second number is the honest one even though it looks worse.

Common questions

How can I tell if a headlamp is regulated?

Brands usually say so, and the burn time chart gives it away: a regulated lamp shows a flat line that falls off a cliff, while an unregulated one shows a steady downward slope from the start.

Is regulated output always better?

It's more predictable, which is what matters when you're planning a night. The downside is that the warning before it fails is short, so a spare battery matters more than it does with a lamp that fades slowly.

Where this is defined

Where this comes up

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

More in lighting and electronics

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.

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.

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