Which Watch Luminous Material Shines the Brightest in the Dark?

Watches have come a long way since the invention of the first pocket watch in the 16th century. One of the most important advancements in watch technology has been the development of luminescent materials that allow time to be easily read in low-light conditions. Luminescence on watches is often referred to as "LUME." In this article, we will explore the history of LUME on watches, from the toxic materials used in the past to the latest and most advanced technology available today.

Early Days of LUME

In the early 1900s, the first luminescent watches used radioactive materials such as radium to make the watch face and hands glow in the dark. This was particularly useful for pilots and soldiers during World War I, as they needed to be able to read their watches in low-light conditions. However, it was soon discovered that radium was highly toxic and could cause serious health problems.

Women painting alarm clock faces, Ingersoll factory, January 1932 Science Museum

In 2018, Juno Films released "Radium Girls," a movie based on true events. The national attention and outrage that followed the well-known Radium Girls case in 1928 had a significant and long-lasting impact on workplace health and safety, as well as the study of radioactivity.

The most well-known incident of radium poisoning occurred with the "Radium Girls," a group of women who worked in a factory where they painted watch dials with radium. They inadvertently ingested the radium by tipping the brush with their lips to keep it straight, causing severe illnesses and even death for many of them. This tragic event led to the discontinuation of radium use in watchmaking and the development of safer alternatives. It serves as a stark reminder of the importance of proper safety protocols when handling hazardous materials, including avoiding putting brushes or other tools in one's mouth and using protective gear when necessary.

In the earlier version of the Panerai Radiomir dial, the radioactive mixture containing Radium-226 was sealed deep inside the dial and protected by a sandwich of thick layers of hardened resin (plexi) and brass.

Over time, the damage caused by the radioactive material becomes visible, as shown in the picture above of a Radiomir Panerai aluminium sandwich dial from WW2, where the inner layer clearly displays the effects of radiation. Radium-226 is not only posed radiation hazards but also lost their luminosity quickly, turning completely dark within a few years and necessitating periodic replacement.

Though the use of radium was not banned till 1968, in the 1960s, the use of radioactive materials was replaced by a less toxic luminescent material called tritium. Tritium is a radioactive isotope of hydrogen, it emits mostly low-energy beta radiation that cannot penetrate the skin and has a relatively short half-life of about 12 years. It emits much less radiation than radium and it is much safer to handle. However, tritium is still toxic if ingested or inhaled in sufficient quantities, so precautions are necessary during manufacturing.

Tritium LUME glows continuously, without requiring an external source of light and it has a half-life, which means it will need to be replaced after a particular period. Tritium was used to make luminescent markers and dials for many years, and it is still used in some watches today.

Diver's Watches and LUME

One of the most important applications of LUME has been in diver's watches. The development of Luminescent materials has been critical to the advancement of dive watches, as these watches rely on clear and reliable readability in low-light or murky water conditions. This means that diving watches need to be able to be read in low-light conditions, as divers often descend to depths where natural light does not penetrate.

Luminescent technology has allowed divers to safely and accurately keep track of their time underwater, helping to prevent decompression sickness and other related hazards. Therefore, luminescent materials have been an essential feature of diver's watches since their inception.

In 1965, Seiko launched its first Japanese diver's watch, the Seiko 62MAS, with luminous hands and hour markers for enhanced readability in low-light situations.

Seiko is one that has played an important role in the development of LUME in diver's watches. Seiko introduced the first Japanese diver's watch in 1965, the Seiko 62MAS. This watch featured LUME on the hands and hour markers, making it easy to read in low-light conditions. Seiko continued to innovate in this area, introducing the first quartz diver's watch in 1975, and the Seiko Quartz Diver's 600m.

Today, dive watches can be found with luminescent dials and markers that are visible even in the deepest and darkest waters, ensuring that divers can stay safe and on time no matter where their adventures take them.

Modern LUME Technology

In recent years, the development of luminescent materials has continued to push the boundaries of what is possible in the world of watchmaking. Today, there are luminescent materials available that can last for days on a single charge and that can be applied to watch dials in a wide range of colors.

The Super-LumiNova lume on the Omega Speedmaster is highly visible in the dark.

Several types of luminescent materials used in watches include Super-LumiNova, LumiBrite, and Chromalight. Super-LumiNova is a non-radioactive photoluminescent material that glows in the dark after being charged by an external light source. It is commonly used in high-end watches such as Omega and Breitling. Super-LumiNova is charged by light and can last for up to 10 hours in the dark. It is available in a range of colors, from traditional green and blue to more exotic colors like orange and pink.

Chromalight vs. Super-LumiNova in the dark

Chromalight is a luminescent material that emits a blue glow that is brighter and lasts longer in the dark. The blue color of Chromalight is said to be easier on the eyes than traditional green LUME, and it is also more resistant to fading over time. One of the Popular Swiss luxury watch band have started using Chromalight in their watches.

LumiBrite from Seiko

Seiko, one of the world's largest watch manufacturers, has been at the forefront of luminescent technology for decades. LumiBrite is a proprietary material developed by Seiko that is both non-radioactive and longer lasting than Super-LumiNova. It is charged by sunlight or artificial light. LumiBrite is a safe alternative to traditional radioactive materials, and it is used in many of Seiko's dive watches, including the iconic Seiko Prospex line.

Impressive LumiBrite (or Lumi Brite) glow of Seiko SKX007 and SKX013 in darkness.

Seiko's use of LumiBrite has made their dive watches some of the most highly-regarded in the industry. The Seiko SKX007, for example, is a classic mechanical dive watch that has gained a cult following for its rugged durability, timeless design, and excellent LUME performance. The SKX007 uses LumiBrite on its markers, hands, and bezel, making it easy to read in low-light conditions.

LumiBrite is a highly effective luminescent material used in Seiko diving watches, including the Seiko SKX013.

Seiko SKX007 diving watch is equipped with LumiBrite, a remarkable luminescent material.

The development of these new luminescent materials has allowed watchmakers to create dials and markers that are brighter, longer-lasting, and more versatile than ever before.

Conclusion

The development of luminescent materials has been a critical factor in the advancement of dive watches, and it has allowed watchmakers to create timepieces that are safe, reliable, and easy to read in any conditions. From the toxic radium paint to the cutting-edge LumiBrite of today, the evolution of luminescent technology has been a fascinating and important story in the history of watchmaking. Today's luminescent materials are non-toxic, longer lasting, and more efficient.

As technology continues to advance, it will be interesting to see what new luminescent materials are developed, and how they will be used in the watches of tomorrow. The future of LUME technology looks bright, with new materials and colors being developed all the time, and one thing is certain: luminescent technology will always be an essential part of the world of dive watches, helping to keep divers safe and on time in even the most challenging conditions.

Written by Victor, images by others as noted and Toni

External References

• All About Super-LumiNova
• Luminor 2020 - Debunking Panerai’s Fictional History Of Tritium-Based Lume
• Lumi Brite
• Seiko 62MAS: A Closer Look At The Brand’s Toughest Diver
• Let There Be Light: Appreciating The Execution Of Lume
• Tales of Lume Watches: Where it all Began