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Discussing the Luminescence Aspect of Watches

Our Luxe columnist and watch expert, Josh Sims, discusses the luminescence aspect of watches…

If, it seems, there is one experience that unites all watch designers it’s the one that happens as a child, under the duvet.

“One of the earliest memories of my dad is him saying goodnight and me quickly charging up the ‘lume’ on my watch under the bedside lamp, so I’d see it glow under the covers for a while when the light went out,” recalls Maximillian Busser, the founder of MB&F.

“It was reassuring then – and I still get some pleasure out of seeing a watch glow. It’s a little presence, a little life.”

Of course, as Don Cochrane, founder of Vertex watches stresses, that many watch hands and indices have been given a lick of some luminescent substance since World War One – when a mix of radium and zinc sulphide was used – is primarily for its obvious practical benefit: so the dial of a mechanical watch is visible in the dark, or deep under water.

But, he adds, luminescence also does much to define the appeal of a watch – it provides the other side of their watch’s personality, a second character that only comes out in the dark.


“It appeals almost at some Neanderthal level, as though some brain chemistry activates when things glow,” he says.

“And it’s an appeal you can’t get from a battery-powered watch light. It’s just not the same.”

Small wonder then that it’s something watch brands are now increasingly exploring more and more – from blocks of lume (as watch buffs call luminescent material), to coloured lume; from artificially-aged lume to all lume dials, such as on the new line from Studio Underdog.

Indeed, the science of watch luminescence has progressed only in small, imperfect if important steps towards achieving the perfect glow – bright and long-lasting.

Evolution and Challenges in Watch Illumination


That radium was once used now seems incredible. After all, it was radioactive, making for watches that were harmless to their wearers but likely shortened the lives of those on the assembly line.

Radium’s use was widely banned in 1968, to be replaced in most instances by a substance called tritium – see dials marked with a T, TT or H3, typically found on US military service watches of the Vietnam era – which unfortunately had a half life of 12 years, meaning the glow eventually stopped glowing.

On the plus side, it did turn to a lovely sepia colour that watchmakers today have a fondness for recreating. Replacing tritium led to a variety of experiments with luminous concoctions, yet culminated in what can seem like today’s near monopoly.

Although it’s not alone, it was the invention of Super-LumiNova by Japanese chemist Kenzo Nemoto in 1993, and the subsequent licence to produce and later develop it by Swiss family company RC Tritec, that would see it come to overwhelmingly dominate the watch market.

Super-LumiNova isn’t a product without problems. It still needs a light source to have the ability to emit light, so if your watch is under your sleeve all day you may be in trouble at night.

And its maker is constantly juggling chemical parameters to alter its decay characteristics – you can have a high brightness initially with lower performance over time, or lower initial brightness with high performance over time, but the best of both worlds is elusive.

You can now have any colour you like, but the darker the shade, the more charging and the less effective its luminescence.

The Evolution of Super-LumiNova


And yet grade by grade, this luminous material – an inorganic ‘high performance afterglow pigment’ made by doping strontium-aluminate oxide powder with Europium, then adding a rare earth material to smooth out the mixture – has improved such that its latest incarnation, X1, launched five years ago, is twice as bright as previous materials and requires less up-front charge to see you through the night.

RC Tritec is now running a project using the latest research techniques to explore new chemical compounds for their luminosity.

“We started out using radium too, but my grandfather found that there wasn’t a big market for radioactive compounds in watches,” chuckles Albert Zeller, the fourth generation of his family to work in the business.

“We tried tritium too. But we’ve continued to advance the Super-LumiNova product and we’re now working on X2. In fact, we only called the latest product X1 because we made the mistake of calling the previous one Grade A, which left us with nowhere to go.

“But just using Super-LumiNova and expecting the best luminescence performance, well, it’s not as simple as that. There are so many parameters – volume, application etc. It’s complex.”

RC Tritec is now aiming for a big push on Lumicast – this is a moulded, 3D Super- LumiNova originally created for industrial use, from which Vertex has carved entire numbers for its dials, providing the brand with a signature look in the process.

And the greater the mass of the luminous material used, the better the brightness, each crystal within the pigment working like a small battery; the more batteries, the higher the light storage capacity.

Watches and Innovation


All the same, concedes Don Cochrane, it’s strange that Super-LumiNova has not inspired challengers, something he attributes to the fact that you need such a tiny amount of the material to produce a glow – indeed, a single gramme, which costs just SWF 15-55, is enough for between 100 and 300 dials, the real cost of the product being in its application.

Yet there have been other, technologically pioneering options. Not long ago the independent brand HYT developed a system that allows energy stored in a mechanical micro-generator to illuminate a cluster of tiny LEDs, and hence the whole dial.

And then there is the return of tritium, this time contained in tiny glass tubes and made any colour you like, as used by Ball Watch and Luminox. Indeed, a reconsideration of tritium makes sense: it’s still a hundred times brighter than Super-LumiNova and doesn’t require pre-charging by exposure to a light source.

“Go to the cinema and you have to be careful to cover your watch, as it’s bright enough to be a light source in its own right,” enthuses Nick Wiseman, UK brand manager for Ball Watch, which has recently managed to introduce the tech into its bezels too.

“It’s really surprising to me that the technology isn’t more widely used.”

Look at the rainbow dials on Ball’s Engineer III Marvelight, for example – in which each of the indices lights up a different colour, enough to light up any small boy with delight and another question entirely arises: if, aside from its practical benefit, the appeal of the glow is so psychologically deep- seated, why haven’t watchmakers used it more creatively?

Watches and their Designs


Certainly, it’s only now, it seems, that they are waking up to luminescent paint as a material with its own expressive potential, especially as new formulas allow luminescence to be put into materials like rubber or ceramic.

Super-LumiNova is increasingly cropping up as a subtle, but alluring design detail – on the bezel, crown and even the strap stitching of Panerai’s Marina Fibratech, for example, or to give the entire case of the Bell & Ross BR-X5 Green Lum that Halloween feel.

Independent watch designers Stepan Sarpaneva, Fiona Kruger and MB&F have worked with lume, so too even more classical brands, the likes of A. Lange & Sohne, have all experimented with luminescence.

Roger Dubuis – which gave the double flying tourbillon of its Excalibur Twofold a glowing green trim in X1 – has even signed an exclusivity agreement on a Super LumiNova product.

Working with lume isn’t easy: put it on a movement, for example, and it becomes difficult to clean or can affect tolerances; different colour combinations can look right in daylight but a mess when all aglow.

But surely we can expect to see more and more watches promoted on the basis of looking as good at night as they do any other time.

“A clever use of Super-LumiNova can give even the most minimalistic of watch designs a cinematic effect, like looking at the dashboard of your car at night,” says Thomas Hohnel, senior product designer for Nomos.

“The result is something magical. And somehow for many watch fans it’s the kind of detail that never gets boring. I think the way watches look in the dark is something customers think more about when they buy watches now, even if they can’t always see the effect at the time.”