Tritium vs lume: one glows on its own and fades, the other is brighter and needs light first

The short version

These two things solve the same problem in opposite directions, and almost every argument about them comes from comparing them at the wrong moment.

Hold a freshly charged lume dial and a tritium dial side by side and the lume wins easily; it is dramatically brighter. Come back six hours later, in a tent, and the lume dial is a faint smudge while the tritium dial is exactly as bright as it was. Neither material changed. The test did.

So the honest question is not which glows brighter. It is when do you need to read the watch.

How tritium tubes work

A tritium marker is a tiny sealed borosilicate glass tube with a phosphor coating inside and tritium gas sealed in. The tritium decays, the emitted electrons excite the phosphor, and the phosphor glows. There is no light input, no switch and nothing to charge. The light is a product of the decay itself, which is why it never goes out while the gas lasts.

That also sets the lifespan. The glow gets dimmer year on year as the gas decays, steadily rather than suddenly, and the makers quote it in decades. Luminox publishes a constant glow for up to 25 years on the 3001, explicitly with no charging and no button pushing. Marathon uses tritium gas tubes on the hands and hour markers of its General Purpose Quartz and on the 41 mm diver, and specifies a dial that pairs tubes with luminescent paint.

The practical consequences of a tube-based system, as opposed to paint:

• Nothing is ever fully dark. Night shift, submarine, cave, inside a sleeping bag: the dial reads the same.
• It is dimmer than fresh lume. Tritium brightness is roughly constant and modest. It is readable, not dazzling.
• It has an expiry you cannot service cheaply. Replacing tubes means replacing the dial and hands, which is a factory or specialist job.
• It costs more. Sealed gas tubes are a manufacturing step, not a coating, which is why tritium watches cluster at the mid and upper end.

How photoluminescent lume works

Modern lume, Seiko's LumiBrite, Super-LumiNova and Marathon's MaraGlo, is a strontium aluminate phosphor in a binder, painted onto hands, indexes or the dial. Expose it to light and it stores energy; in the dark it releases that energy as visible light, decaying quickly at first and then slowly over hours.

Three things follow, and they are the mirror image of tritium:

• It is far brighter at first. A well-lumed dial after a minute under a lamp is bright enough to read across a room.
• It needs a light source. A watch kept under a sleeve all day, or in a dark cab, charges poorly and will be faint by midnight.
• It lasts forever. There is no decay clock. Strontium aluminate lume on a thirty-year-old watch still charges and glows, which is exactly what tritium cannot do.

Seiko states LumiBrite on the hands and indexes of the 5 Sports SRPD51, and Marathon pairs MaraGlo with its tritium tubes, which is a sensible belt-and-braces approach: the tubes give you the always-on baseline, the paint gives you the burst of brightness after exposure.

The comparison that matters

When a backlight beats both

There is a third answer, and on this site it usually wins: an electrically lit display.

Every Casio on this site has either an EL backlight that lights the whole dial, as on the DW-6900 and DW-9052, or an LED. Garmin goes further and puts a real flashlight on the Instinct, fenix, tactix and Enduro lines, with variable intensities, a red mode and a strobe. A red mode is the detail that matters for anyone whose night vision is working, and the tactical Garmins use a green light for the same reason.

So the full hierarchy for reading a watch in the dark is: a backlight or flashlight beats everything when you can press a button; tritium beats lume when you cannot; and lume beats tritium in the first few minutes after exposure to light. If you want the light-discipline version of this argument rather than the brightness one, the watches built for it are in best tactical smartwatch, and the night-vision-compatible red backlight on the Suunto Core Alpha is covered in best ABC watches.

The picks

How to choose

Buy tritium if you are woken in the dark, work nights, sleep in a vehicle or a tent, or want to read the time without pressing anything and without having charged the dial first. The trade is a dimmer dial than fresh lume and a glow clock measured in decades. The watches that do this best are in best military watches.

Buy lume if your watch sees daylight before dark, if you want maximum brightness for the first part of the night, or if you want a dial that will still light up in forty years. It is also the cheaper technology by a long way, which matters if you are spending the difference on a better case or a better power system.

Buy a backlight if you are honest about how you actually check a watch in the dark, which for most people is: press the button. Every Casio here has one and every Garmin outdoor watch has a flashlight, and neither has a decay clock.