The need to read the time in the dark has been a challenge for the makers of timepieces for hundreds of years. The first solution was not a visual but an audible one: watches that could chime the current hour and minute on demand. These types of watches, aka minute repeaters and sonneries, are quite rare and expensive today and regarded as luxuries rather than the utilitarian inventions they initially were. In the 1900s, a more practical option presented itself: treating a watch’s dial with luminous paint that made its time display visible in darkness. And while this approach proved to be much more cost-effective and practical, it also brought a new set of challenges, as the earliest substances used on the dials were discovered to be unsafe, for the people who made the watches and, to a lesser extent, those who wore them.
Let There Be Light
The first material applied to watch dials for nighttime luminescence was radium paint, which, thanks to radium’s half-life of 1,600 years, offered a long-lasting glow during that period before dimming — the catch being that, as its name implies, radium (specifically Radium-226, which was used as the base of the “Radiomir” substance registered by Guido Panerai ) is radioactive. In the 1920s, the mostly female factory workers that painted the watch dials with radium compounds started falling ill and dying at alarming rates, leading to lawsuits against the companies that produced the material and eventually, safer working conditions and an abandonment of radium as a luminous substance in watchmaking by the 1960s.
Replacing radium for a short time as the luminous substance on watch dials was a compound called Promethium (Pm-147), which was less radioactive but had a half-life of only two-and-a-half years and thus a much shorter period of luminescence. Next up was Tritium H-3, a radioactive isotope of hydrogen with a respectable half-life of 12.3 years and, as a low-energy beta emitter, far less hazardous to work with than radium. Tritium, which was used in small amounts to boost the explosive power of the atomic bomb detonated on May 1951 over the Enetawak Atoll, was not entirely without risk, however. Used on surfaces like dials, tritium had a tendency to diffuse, seeping through the case and into the skin of a wearer. Tritium-based paints on dials, which was used by numerous watch brands, including Rolex, was banned in 1998.
The use of tritium has for the most part been entirely supplanted by a non-radioactive luminous substance that traces its origins all the way back to 1941 and a Japanese inventor named Kenzo Nomoto. Contracted by the Japanese military to make luminous paint for the gauges of WWII-era aircraft, Nemoto turned his attention to creating a phosphorescent, non-radioactive type of paint to apply to watch dials after the end of the war, founding the company in 1962 that would eventually develop LumINova in 1993. Unlike all the materials that preceded it, LumiNova — called Super-LumiNova by the firm that makes it entirely in Switzerland — was different in that it acts as something of a light absorbing, energy-storing battery. The substance doesn’t glow on its own but needs to be activated, or “charged,” by an external light source; in essence, the light your watch dial absorbs during the day is ideally enough to make its luminous elements glow brightly at night, after which it will require charging again the next day. LumiNova, or Super-LumiNova, is ubiquitous throughout the watch industry today, even more so than most imagine: Rolex’s ChromaLight and Timex’s IndiGlo, to name two trademarked substances, are re-branded types of LumiNova.
Tritium Goes Tubular
Tritium, however, still had its adherents in the watchmaking business — particularly among those companies with military clients — even after Super-LumiNova was nearly universally adopted by watchmakers as the go-to luminous substance for dials. Tritium is, after all, still a brighter and longer-lasting luminous material than Super-LumiNova, and it doesn’t require an outside light source to “charge it up” for the nighttime hours. How then, to use it safely? A clever solution presented itself in the late 1990s, one now embraced by the few watch brands that not only still use tritium regularly but have adopted its use as a marketing tool. The GTLS (gaseous tritium light sources) process involves inserting small amounts of the H3 gas into tiny narrow glass tubes (pictured above), which are less permeable than a watch crystal over the dial and also have been treated on their inner surfaces with luminous powder that is activated by the electrons in the gas. The tubes are then strategically placed at key parts of a watch’s dial, under the crystal, for maximum lighting effect — traditionally, the hands, hour markers, and numerals. Fans of these modern “tritium watches” — most of them decidedly positioned as utilitarian tool watches rather than luxury objects — cite their super-bright nighttime glow as one of their most appealing features. As with Super-LumiNova, recent years have seen a proliferation of different-colored H3 gas tubes that not only make for more eye-catching visual effects in low light but can also improve legibility in those conditions, with different colors used to identify different markers and indicators. Below, we spotlight several watch brands that still proudly offer tritium watches in their lineup.
BALL WATCH COMPANY
The most prominent maker of tritium watches, and the one that occupies the highest level of luxury in both craftsmanship and cost, is Ball Watch Company, which traces its origins to 1891 in the United States and is now based in La Chaux-de-Fonds, Switzerland. Founded by Webster Clay Ball, a Cleveland jeweler and Chief Inspector for the Lake Shore railway line, Ball Watch built its reputation on its dependably accurate railroad watches, which were officially adopted as “Railway Standard” and worn by train conductors and other railroad workers throughout the early part of the 20th century. This dedication to “industrial function” drives the brand to this day: Ball Watches are known for technical innovations like patented anti-shock and antimagnetic systems, chronometer-certified movements, and its “Night Reading Evolution,” aka its use of H3 micro gas tubes for illumination. Pure, stable tritium gases are encased in tiny tubes whose interior surfaces are coated with luminous materials that are activated by the gases’ release of electrons. The tubes are mounted in such a way as to be nearly unbreakable, and Ball assures us that the level of radiation actually emitted by the tubes is negligible. According to Kevin Kouch, Executive Director of Ball Watch Company, "The gas is very well protected, and even if a tube should break, the gas will evaporate safely. You're really exposed to more radioactivity when you're out in the sun."
Nearly every Ball Watch model incorporates tritium into its dial, but a handful of watches are distinguished by high numbers of micro-gas tubes and a plethora of glowing colors. “We started out using very little amounts of tritium, on dials and hands only," says Kouch. "It was not as complicated as today, when we are revolutionizing the use of tritium with many different types of colors and using it on bezels and underneath the sapphire crystals and lots of other different applications.” Kouch points to two standout models that are available now: the Engineer Marvelight III Chronometer Caring Edition and the Engineer Hydrocarbon NEDU. The former (below), released in summer of 2020, is a watch developed to honor those affected by the COVID-19 pandemic, with $300 of the proceeds from the sale of each watch donated to the Salvation Army. The black dial uses a total of 27 micro-gas tubes, including the large ones serving as the hour markers in a dazzling rainbow of colors. Ball Watch’s hallmark codes are also present on the dial, including the historic, railroad-inspired “RR” counterweight on the seconds hand. The COSC-certified Ball Caliber RR 1103-C is guarded against shocks by the company’s proprietary Amortiser system and against magnetism up to 80,000 gauss by an inner cage made of “mu-metal,” an alloy of nickel, iron, copper, and molybdenum with a high degree of magnetic impermeability. The stainless steel case, in 40mm or 43mm sizes, has a screw-down crown to ensure a water resistance of 100 meters. Limited to 1,000 pieces, the watch retails for $2,199. Check out Teddy's review of the Caring Edition here.
The Ball Engineer Hydrocarbon NEDU (below) is a rugged diver’s chronograph built for the specific needs of the Navy Experimental Diving Unit (NEDU), the unit responsible for determining the operational diving and decompression rules for the entire U.S. armed forces. Its 600-meter water-resistant grade 5 titanium case is 42mm in diameter and features a helium-release valve and a patented crown protection system. Distinguishing the model is its incorporation of luminous paint directly onto the numerals of the unidirectional divers’ bezel, made of chromed pure ceramic, a material boasting extreme resistance to corrosion, scratches, and ultraviolet rays. An additional 21 H3 micro-gas tubes appear on the hands and hour markers of the dial. The automatic, COSC-certified Ball RR1402-C caliber beats inside, powering the time display, 12-hour chronograph, and day-date display at 3 o’clock. Mounted on a rubber strap or a titanium-and-stainless steel bracelet, the NEDU retails for $4,649. (You can shop for Ball Watches here.)
Founded in 1989 by watch industry veteran Barry Cohen, Luminox takes its name from a portmanteau of two Latin words, “Lumi” for light and “Nox” for night, an indicator of the Swiss brand’s commitment from the get-go to “offer cutting-edge luminescence and readability in its line of high-performance sports watches.” Luminox is best known for making watches worn by Navy SEALs and other military units and for its partnership with “Man vs. Wild” star and survival expert Bear Grylls. Luminox touts its LLT (Luminox Light Technology) as holding a constant, bright 24/7 glow for up to 25 years thanks to the use of tritium gas inside borosilicate glass capsules (aka micro gas tubes). The need for such functionality, Luminox says, is what inspired Navy SEAL team members to lobby the brand for the military-grade dive watch now known as the Original Navy SEAL Watch.
The latest version of that tough, tactical timepiece, which originally debuted in 1992, is this year's Navy SEAL RSC 3250 (above), commemorating 30 years of Luminox's partnership with the SEALs. The watch's robust, 45mm “turtle” case combines three materials: rubber, steel, and, for the ratcheting unidirectional bezel, Luminox’s proprietary Carbonox material, which is prized for its durability while still being exceptionally lightweight. A screw-down crown with double security rubber gaskets helps ensure a 200-meter water resistance and protects the Swiss-made Ronda 715 LB395 quartz movement, which holds a 50-month battery life. Four models of the RSC 3250 are available, ranging in price from $595 on a rubber strap to $695 on a steel bracelet.
The Traser brand traces its origin to a specific watch developed by Bern, Switzerland-based mb-microtec — the company that would later work with Ball Watch to develop its own light technology — at the request of the U.S. Army. That watch, the P6500 Type 6, was built to MIL-W-46374F military specs and was, Traser says, the first self-illuminated watch. The brand spawned from that successful experiment retains the military influence, focusing on tactical, outdoor, and diving watches with highly functional designs and all using what Traser calls its “trigalight” technology, with tritium gas hermetically sealed into laser-cut glass tubes just slightly thicker than a human hair, which are placed at strategic positions on the dials. Traser watches are Swiss-made, with quartz or automatic calibers, and priced around $500 to just over $1,000.
Since 1939, when it was founded by Morris Wein, Canada-based Marathon Watch has been making timepieces for the North American market and since war-torn 1941 has been supplying them to the U.S. armed forces. (Today, the company is the sole supplier.) Now manufactured by the fourth generation of the founding family, Marathon watches — designed in Canada, manufactured in Switzerland —have become well regarded for their military durability and mission-ready precision. A functional military watch needs to be readable at all times in all situations, hence Marathon’s use of H3 gas tubes on its watches’ dials. The purest example of Marathon’s utilitarian design is represented by the General Purpose Mechanical Field Watch ($450, above), with a 24-jewel, dual-winding movement (manual or automatic) inside a 34mm case made of 316L stainless steel. The black dial (there's also a "U.S. Army" official version with an Army star at 12 o'clock) hosts brightly glowing tritium tubes at the 12 hour markers, which surround an additional 24-hour (military time) scale. You can shop for Marathon Watches here.
Why are tritium watches so rare in today’s market? As should be clear by now, it’s not due to any danger their minimally radioactive elements represent. It’s likely that the cost and technical expertise required to utilize the GTLS technology is prohibitive to many, particularly the makers of luxury watches that don’t require extreme, tactical levels of 24/7 luminescence. As Ball Watch’s Kouch points out,”Not many other brands have chosen to explore it. There are a lot of technicalities involved, including with the movement. The height of the handset has to be taller when there are tubes on the dial, for example. Everything has to be modified; it’s not just a standard movement from ETA." One thing is for certain: tritium watches will have their fans as long as there are watch wearers obsessively checking the time in dark conditions.