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Luminosity in Watches

by Hours and Minutes Australia

Throwing some light

Have you grappled for the switches in the dead of the night, but were grateful to that luminescent clock in your room? Have you ever dived deep down in murky waters, thankful that the dial of your watch provided all indications glowing… pun intended!

Luminous watches are very common today, but they have a long history. This history is somewhat linked to the idea of glowing luminous objects. Luminescent pigments occurring in natural stones (such as jade) were often used in the past. They were ground and put on jewels and wine cups, adding oodles to the look and the preciousness of the piece as well.


It is said that the first luminous paint was invented in Japan over 1,000 years ago. China and Japan are the civilizations who started using this paint on paintings and other objects, but it was a matter of time that they found another useful expression on dials of watches. The technique reached Europe and Swiss watchmakers began treating the dials of timepieces with a natural luminescent paint, created using the same technique as the early Japanese artists.

These early experimentations may not reflect the great quality of luminescent materials that we have today. In fact, the luminosity of these objects in the past was often low and faded quickly in a couple of hours. Even today, this kind of inferior quality is used on cheap toys and watches.


While most radio-active substances are not used any more for luminosity in watches, tritium based devices called “gaseous tritium light source” are popular since they are self-powered and produce a consistent luminosity that does not fade during the night, but, in the end are radioactive. Tritium filled tubes which come in different colours like orange, blue, green or red and are coated with phosphor to create the glow are called trasers. The Tritium gas is sealed within the glass tube, so though they are radioactive, they do not emit any radiation. They also have a life of about 12 years or so which will gradually fade, becoming too dim to be useful after 20 to 30 years.


Many watch groups have come up with their own versions of luminous substances. Luminox Light Technology is a system used in Luminox watches. It is a self-powered illumination system discovered in the 1980s, and uses micro gas light tubes, called borosilicate glass capsules, in the hands, the hour markers and, in some cases, the bezel of the watch. The light tubes glow constantly for up to 25 years and keep the watch bright for perfect at-a-glance visibility, even in complete darkness. Seiko has developed LumiBrite, a luminous paint which is long-lasting, bright and completely free from radioactive substances. The paint glows brightly when it is first in the dark and then slowly fades. Citizen watches right across the range use Natulite luminous paint.


There were some significant experiments and innovations that changed the game. The most popular one, and the one that is widely used today, is Super-LumiNova. This makes use of strontium aluminate, which is non-radioactive. It also used nontoxic afterglow pigments, offering much higher brightness than pigments used in the past. The way it works is, the ultra-violet radiation in daylight and in some artificial light sources adds energy to the electrons in  strontium aluminate pigment, which then slowly releases it in the form of photons or light over the course of the next few hours. This is the simple working of this pigment.

Super-LumiNova is based on LumiNova pigments. The parent company credited with this invention is Nemoto & Co., Ltd. of Japan, who came out with this wonderfully safe replacement to radium in 1993. Rolex has its own version of the luminescent paint, called Chromalight. Patented in 2008, it glows blue in the dark.

Super-LumiNova has found widespread application in the watch and clock industry. It has also been used for markings on various scales and instruments, including aviation instruments and emergency signs, aiming posts and so on. The printing industry as well as the fashion industry have also made many creative uses.

The success of the use of Super-LumiNova in watches is also dependent on how it’s used. For example, Panerai uses a layered dial with SuperLuminova at the core and numerals cut out from the top layer. This enables more of the pigment to be used, and is directly proportional to the quality.


It’s only been around since 1998 and the watch industry will have to wait to study the long term effects on the quality of light emitted by the watches that use SuperLuminova or Luminova. What we do know is that moisture causes it to crumble. Hence, watchmakers protect the pigment using a thin coating of transparent lacquer. This could possibly age over time, but then, only time can tell! Till then, Lumos….Let there be light!

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