Lume 101: All About Watch Luminescence

Have you ever wondered how some watches glow in the dark?

We are going to tell you all about luminescent paint – or lume. A range of materials have been employed by watchmakers over the years to make parts of a watch glow, increasing functionality in the night time.

Let's dive into some history that will allow you to better understand how these glow-in-the-dark hands, dials, numerals, hour markers and other parts have been made.

 

Lume can help make your watch visible at night - or make it look extraterrestrial. Source: suretimemods

 

The lume effect in a watch can be obtained by using a variety of materials. The watch industry has experimented with several types of lume solutions – some of which were very dangerous!

The duration of the lume effect depends on the type of lume employed, as well as the amount of it that is used. Some watchmakers apply a single layer of lume to a watch, while others apply many layers to ensure that the watch not only shines brighter but also lasts longer.

 

Some History: The Journey of Luminescence in Watchmaking

Humans have been looking for new and improved ways to see objects in the dark since the discovery of fire.

The modern wristwatch appeared towards the end of the nineteenth century. On the first few years since its invention, these timepieces were only seen on wrists of wealthy high-class ladies (gentlemen favored the pocketwatch), and pilots who used them to keep both hands free while in midflight.

 

 Now, pocket watches have become a fashion item.

 

Following the First World War soldiers began wearing wristwatches so that they could read the time quickly when needed instead of having to take a watch out of their pocket. With this development, the global demand for high-quality wristwatches increased.

Watch luminescence became necessary when soldiers needed to tell the time without having to light a match or use a flashlight on the combat front.

Since then, the efficiency of watch luminescence has varied over the decades with the constant innovation of improved glow-in-the-dark materials and techniques.

 

When Lume came with a side of Radioactivity

At the beginning of its development, glowing watches were dangerous. Radium was utilized to make the original lume, which was hazardous to the wearer of the watch but even more so to watchmakers who painted the substance into the dials.

 

Ladies unknowingly working with dangerous materials. 

 

A working-class lady could make a fair living painting luminous material onto watch dials in the 1910s and 1920s. It became an appealing job that demanded artistic ability.

The novel lume technology was cutting-edge at the time, and employees got satisfaction in contributing to the First World War effort by making legible watch dials for soldiers.

The lume material was applied with a precision-brush, which was usually pointed with the tongue to keep the bristles sharp. It is also known that workers even played around by painting their fingernails with the phosphorescent material as well.

 

Today, nobody would even go near something glowing like this until they know for sure that it's not radioactive. Source: Economic Times

 

The substance in question was radium, which generated a bright glow when combined with zinc sulfide (a phosphor).

 

A Few Problems in the Early Days

Despite the fact that plant owners and scientists took precautions while handling bigger quantities of radium, the working women were persuaded there would be no adverse effects from the close exposure to the chemical.

When those women began to develop anemia, bone fractures, jaw necrosis, and eventually death, it became evident that these ladies had been neglected and deceived.

 

The story of Radium Girls are truly a tragic one. Source: BuzzFeed

 

In 1927, Grace Fryer and a group of other dial painting women, dubbed the "Radium Girls", filed a lawsuit against the United States Radium Corporation, their employer. This historical litigation opened the way for improved legal protection for workers in the United States as well as tighter industrial safety rules

Radium's use was thereafter drastically reduced. By the 1960s, the amount of this material used in watch dials had dropped to around one-hundredth of what it had been in the early 1900s, to finally be completely banned in 1968.

 

Switching to a “Safer” Alternative

Tritium, a new radioactive element, emerged as a successor. Plastic case backs were common on watches that utilized Tritium paint-based luminescence.

 

Despite being radioactive, Tritium is apparently safe enough to use as a night light. Source: Hackaday

 

This innovation had to be implemented since Tritium diffused and made its way into the dial, crystal, and case back, where it might then reach the skin of the person wearing the watch.

Tritium is far less radioactive than radium, therefore safer to use on watch dials for decades until the early 1990s, when it was widely replaced by a pair of even safer replacements that are still in use today.

Tritium though is currently called GTLS (gaseous tritium light sources) and is still used by a few watchmakers in the industry: Ball, Luminox and Marathon.

 

Radiation is not emitted as much through these glass tubes. Source: Assignment Point

 

GTLS is safely housed in very narrow glass tubes that are less permeable than the paint on a dial that is just protected by the watch glass. When the crystal and case backs are what is now known as GTLS-glass tubes, it is further protected.

Yet, in countries like Germany, watches that employ GTLS are not allowed to be built.

GTLS is ideal for tool watches because, unlike modern types of lume, its luminosity does not fade after a few hours. With a half-life of about 12 years, barely a fifth of the radioactive material is remaining after around 24 years.

Many watchmakers, including the most well-known luxury watch company, Rolex, have used tritium over the past. Rolex abandoned the use of tritium after its use as a lume paint was outlawed in 1998. Since then, Rolex has been using its own version of Luminova instead.

 

The Invention of Luminova by Kenzo Nemoto

In 1941, a Japanese man named Kenzo Nemoto started a business selling phosphorescent paint. During World War II, he was hired by the Japanese military to paint the gauges on airplanes and submarines.

When the war ended, he was no longer painting for the military and had to seek out new consumers. Nemoto primarily supported himself by painting the hour markers and hands on residential clocks, before moving on to watches.

The Japanese entrepreneur began thinking about how to develop a new non-radioactive luminous material not long after the bombings of Hiroshima and Nagasaki in 1945, at a period when the Japanese were increasingly wary of the dangers of radioactive elements.

Nemoto Company Logo Source: Nemoto.co.JP

 

While developing a novel phosphorescent substance, Nemoto founded the Nemoto & Co firm in 1962, which by 1993 finally offered a new type of luminescence to the watchmaking industry.

The new substance, Strontium Aluminate, is a revolutionary, non-hazardous phosphor that does not degrade over time, is temperature-resistant, and is unaffected by environmental factors.

In 1998, Nemoto partnered with swiss-based RC-Tritec AG* to form LumiNova AG Switzerland, a branch that would soon supply the watch industry with “Super-Luminova” paint, the commercial name of the glowing substance.

 

Whoever thought up the name Super-LumiNova is a marketing genius. Source: WatchGecko

 

Nemoto patented Luminova’s formula, and then sold it to watchmakers eager to participate in the next level of glow-in-the-dark technology.

LumiNova was around ten times brighter than previous lume, and it came in a variety of colors ranging from brilliant blue to bright green. The blue hue was found to glow the longest, but the green hue was found to glow the brightest.

To make this new material glow, it needed to be mixed with a chemical element called Europium. Unlike its predecessors, LumiNova becomes “charged” when exposed to light, whether natural or artificial, and gives greater nocturnal visibility.

You can think of LumiNova as a light storage battery. Although artificial light can also charge the lume, it is said that sunshine has the best effect. When light strikes phosphorescent material, it excites electrons and causes them to rapidly charge.

 

A matter of Photoluminescence

Today, the most often used watch lume pigments are those based on photoluminescent materials such as Strontium Aluminate or LumiNova.

 

 You can make all kinds of cool stuff with this material.

 

This substance is painted onto hands, numerals, and dials, and subsequently glows in the dark (typically in a green or blue tint) by absorbing and re-emitting light.

The disadvantage with Luminova is the shorter duration of the glow – it usually lasts around seven hours or so in the darkness which is remarkably less compared to the yearly time-span that former radioactive solutions granted.

The Swiss company founded by Kenzo Nemoto and partners is now one of the leading providers of photoluminescent paint However, other watchmakers, such as Seiko and Rolex, produce their own proprietary formulas.

 

Another Way to Glow: Electroluminescence

The generation of light by an electrical current traveling through a phosphor is known as electroluminescence.

In a watch, an electric conductor and phosphor are placed on a glass or plastic panel positioned behind the dial. An electric current is given when a button is pressed, causing the phosphor to respond and operate as a backlight.

 

Timex likes to do things differently. Source: Reddit

 

Though most typically used in digital watches, Timex's Indiglo is the most prominent analog watch to feature this form of ‘backlight’ illumination. Timex patented the technology in 1992, making it one of the few analog watch manufacturers with this form of lume.

 

Seiko’s Proprietary Lume

LumiBrite (or Lumi Brite) is a stunning sort of luminescence available in Seiko divers ranging in price from a few hundred dollars to thousands of dollars. It is based on the LumiNova technology developed by Kenzo Nemoto.

Seiko’s LumiBrite is fully safe for humans and the environment, as it contains no toxic ingredients or radioactive substances.

LumiBrite is an enhanced luminous paint that absorbs and stores light energy from the sun and lighting apparatus in a short amount of time, allowing it to radiate light in the dark.

 

This much brightness makes the watch easy to read even in the dark depths of the water when diving. Wikipedia

 

In a single sentence, Jiro Uchida, president of Seiko at the time LumiBrite was introduced, said:

“Lumibrite is a virtually permanent, non-radioactive, fluorescent coating that can light up the face of a watch, or just its hands and numbers, for up to five hours after two minutes exposure to sunlight.”

Seiko began using LumiBrite as far back as 1994.

Seiko LumiBrite watches were introduced around the same time as Timex IndiGlo watches. Notably, Seiko's advertising campaign in those days highlighted the fact that LumiBrite is ten times brighter than ever before (than LumiNova) and ‘with no buttons to push’.

 

NamokiMODS Lumed Seiko Mod Parts

Seiko modders, especially those beginning to mod, should know that high quality luminescent Seiko mod parts are out there, and work well with both OEM parts – or with aftermarket builds.

Seiko mods are an excellent way to personalize classic Seiko designs. At NamokiMODS, we make aftermarket Seiko mod components that meet – if not exceed – OEM specifications. SKX007 mod parts or other Seiko divers mod parts from NamokiMODS offer incredible value, and with top notch fit and finish.

We offer a wide range of lumed hands, bezels and dials with two available lume colors: C3 (white in the light, green in the dark) and BGW9 (white in the light, blue in the dark).

The brightness scale of photoluminescence colors is defined in comparison to C3, which has a brightness of 100% in the grading system. BGW9 has around 95 % brightness compared to C3.

 

 

For example, C3 Super-LumiNova® Lume is used to light up the hands of the Seiko 62Mas handset we create, and also used on loads of our SKX style watch parts. You can find the complete range of NamokiMODS’s lumed hands here.

Also, NamokiMODS’s lumed bezel inserts (lumed ceramic and lumed glass) come in new colours to suit almost any build. Check out the SKX007/SRPD Lumed Glass Bezel Inserts at NamokiMODS’s online store.

 

 

You can find a complete range of NamokiMODS lumed bezel inserts here! Some versions are conservative and only keeps lume in a button-like pip located at the 12 marker. Other bezel inserts go all-out, with glowing indices and numerals.

 

 

We also use top-quality lume on all our dials, so check out all the options we have for you! Some of our most popular dials are the Divemasters and MarineMasters, so be sure to check them out!

C3 Super-LumiNova® Lume is used in all of the lumed parts we make and will closely match the intensity and brightness of stock Seiko LumiBrite parts.

If you love diver’s watches – you probably love lume as much as we do. Dive into our website for a wide selection of some of the best aftermarket Seiko mod parts in the world!