What Is Watch Lume? Why the Dead Kind Sells

The best lume I've ever handled was on one of the cheapest watches I've ever handled and almost nobody selling you a watch will say it out loud. Every reviewer ends on the same shot: lights off, dial to the lens, a voice going "look at that glow." The watch that wins that shot is almost never the one worth keeping. The compound behind the glow costs pennies, and it's the same across the industry. How neatly it's painted on tells you something about the finishing. The glow itself tells you almost nothing.

The lume that actually moves money is the lume that stopped working years ago.

The lume that sells is the lume that quit.

I should say up front: I don't sell vintage. I sell modern independents, which means the lume on everything I handle is about as good as lume has ever been — bright, even, lasts the night. And it adds almost nothing to what any of those watches are worth. The vintage market is where it gets strange. There, a dial with its original tritium — uneven, gone to cream, stone dead after dark — is worth more than the same watch wearing a fresh coat of lume that actually works. Sometimes twice as much. The market doesn't want the lume to work. It wants the lume to be original, and original tritium from 1974 does not work.

Here's the thing the lume shot never explains. There are only two ways to make a watch glow in the dark, and they're opposites.

The first makes its own light. You take something radioactive, mix it with a phosphor, and the radiation excites the phosphor into glowing — constantly, no charging, day and night, for as long as the isotope holds out. The second borrows light. A phosphor soaks up daylight or a UV torch, traps the energy in its crystal structure, then leaks it back out as a glow that fades across the night. Everything modern is the second kind. Almost everything collectable is the first.

Tritium's half-life is twelve years.

Half-life means half the glow is gone every twelve years. A tritium dial from 1974 has been through four of them. What's left is maybe a sixteenth of what it carried out of the factory, which is to say nothing — a warm, dead, cream-coloured nothing that the market has decided is one of the most desirable things a vintage watch can have.

Radium

Start with radium, because radium is where the horror is.

From around 1917, the glow on a watch dial was radium-226 mixed with zinc sulfide and painted on by hand. In the US they sold the paint as Undark. The hand-painting was done by women — in New Jersey, in Illinois, in Connecticut — who were told to keep a fine point on the brush by drawing it between their lips. Radium behaves like calcium in the body. It went into their bones. The jaws of the dial painters rotted; they developed anaemias and cancers and fractures that wouldn't heal, and the lawsuits they brought in the 1920s and 30s helped establish the idea that a worker could sue an employer for an occupational disease at all. The Radium Girls are the reason your watch isn't painted with radium today.

And here's the irony that runs under the rest of this. Radium-226 has a half-life of sixteen hundred years. The radium in a 1940s dial is still radioactive — you do not sand one, you do not breathe the dust — but the zinc sulfide phosphor it was mixed with died decades ago, killed by the very radiation sitting next to it. So a radium dial is the worst of both: hot enough to need careful handling, dark as a coin after midnight. It makes its own light, and it gave up making it a long time ago.

Tritium

Tritium replaced radium from the 1960s, and it replaced it because it's far less likely to kill the person wearing it. Tritium is hydrogen-3. It throws off a low-energy beta particle that a watch case — or your skin — stops cold, so a tritium dial is radioactive in the most technical and least frightening sense. You'll see it confessed on the dial in small print: T SWISS T, or SWISS — T<25, meaning tritium, under twenty-five millicuries. Collectors read those few characters like a date stamp.

Take the Rolex Submariner 5513 — made from 1962 to 1989, and one of the most-collected vintage dive watches there is. The lume on a good one has gone the colour of weak tea, or if you're lucky something nearer pumpkin, and it does nothing in the dark. That dead, even, untouched cream can add thousands to the price. A 5513 with relumed plots — lume that works again — is the cheaper watch. The market took a feature that no longer functions and priced it above the same feature in working order. It did that on purpose, for a reason worth getting to.

Super-LumiNova

Then in 1993 a Japanese company called Nemoto worked out how to make a phosphor that didn't need a radioactive engine behind it. Strontium aluminate, doped with europium and a trace of dysprosium — the europium does the glowing, the dysprosium builds tiny traps in the crystal that hold the charge and leak it out slowly, which is why the stuff glows for hours instead of seconds. They called it LumiNova. It was roughly ten times brighter and longer-lasting than the old zinc-sulfide phosphor paints, and it would never give anyone bone cancer. The Swiss firm RC Tritec licensed the technology and, through a 1998 joint venture, turned it into the fully Swiss-made version everyone now calls Super-LumiNova. Seiko's take on the same chemistry, LumiBrite, arrived around the same time.

It is also the lume on almost every watch made since. Same chemistry, a handful of grades, sold by the gram to anyone who asks. The Super-LumiNova on a £200 microbrand diver and the Super-LumiNova on a £6,000 one come off the same shelf. There's a tritium-tube branch too — tiny glass vials of tritium gas, phosphor-coated on the inside, glowing on their own for a couple of decades with no charge, which is what Ball and Marathon and the rest stamp "H3" for — but that's a tool-watch sidebar, not the main road.

Rolex's version is the famous one. Chromalight, out since 2008, glows blue instead of green and outlasts standard Super-LumiNova — Rolex will tell you so, and they're right. It is the best lume on any Submariner ever made. 

The inversion

So here's the received wisdom, the thing the lume shot is built on: bright, even, long-lasting lume is a sign of a serious watch. Flip it. In the second-hand market, lume quality runs almost exactly backwards to value.

Put a £300 Seiko diver next to a 5513 in the dark. The Seiko torches — a hard green slab you could read across a room, holding for hours. The 5513 gives a faint, patchy whisper, then nothing. The Seiko wins the reviewer's shot by a mile. The 5513 is worth many times over what the Seiko costs. Every lumen of advantage the Seiko has is an argument for the Seiko that the market refuses to hear.

Because the glow was never the point. Working lume is a feature, and a free one — it comes in the box, it works the same on every watch in its bracket, and a feature everyone has is a feature nobody pays a premium for. Dead lume is something else. Dead lume is a clock that says how old the watch is, evidence the dial hasn't been redone, and a colour the factory CANNOT reproduce on purpose, however hard it tries — because the colour is decades of oxidation and decay, and you can't shortcut decades. A relume, even a good one, is worth less, because the thing being bought is originality, and a fresh coat of lume is the opposite of that.

The lume that sells is the lume that quit.

You're not paying for light. You're paying for time you can see, and for the proof that the watch in front of you is the watch that left the factory.

What you're actually buying

None of this means the glow is worthless to you, the person who actually straps the thing on. A dive watch you can read at 2am is doing its job. A fresh hit of Super-LumiNova on a watch you bought to wear is exactly right — it's the honest choice, and it's most of what I sell. The independents I stock put genuinely good lume on their watches. It works, it lasts the night, and it is the least valuable thing about any of them. I'm not going to tell you the glow is why you should buy one.

So know which thing you're buying. If you want lume that works, buy modern and stop reading the dial markings. If you want the lume the market pays a premium for, you're buying a dead battery and the story of how it died — and the story is the point, not the light.

Buy the dead one for the story. Buy the bright one to tell the time. Don't confuse the two.