One specification that can make or break a watch for some consumers and certifications is the quality of its lume, referring to the luminescent material applied to the dial or hands. In a process very similar to glow-in-the-dark star stickers that you’d put in a kid’s room, most lume is a paint that gives off light for a couple hours after itself being exposed to light. The strength and longevity of this glow is a indicator of its quality, but even the most expensive Swiss lume will eventually fade to black before the sun rises again. And there’s nothing wrong with that- it’s just a limitation of the material!
But phosphorescent paint isn’t the only method- some manufacturers opt for tritium vials for lume instead, but why? Tritium, or H3, seems a bit like magic to the untrained eye. It is a tube that will faintly glow for decades, with no sunlight or batteries or movement required. So how does it work?
Tritium tubes being used as both hands and dial markers.
Tritium tubes are large enough for the eye to notice their shape- and they are a very interesting visual component of a dial.
To answer this, we’ll look at the science behind the material. If you have no background in Physics or Chemistry, no worries! This article is designed to be easy to digest for everyone. We will split the question into 3 parts:
What is Tritium?
What’s With The Tubes?
Is It Safe?
What Is Tritium?
Starting with the basics, we have to know what tritium is. Tritium is an isotope, which just means it is a variant of an element. In this case, it is a variant of the most basic element, Hydrogen. Hydrogen is a single proton with a single electron orbiting it. Tritium is the same thing, with 2 neutrons added into the nucleus with the proton.
Photo Credit to BYJU’s.
H1, H2, and H3’s diagrams shown side by side.
What protons/neutrons/electrons are, or how you’d put neutrons into Hydrogen isn’t really the scope of this article. What is important to know is that Tritium is unstable, which means that it won’t stay Tritium for long. Eventually, the element will morph itself into something else entirely. For Tritium, it will eventually decay into an isotope of helium, and shoot out a electron in the process. This is called beta radiation, and means that Tritium is radioactive. It has been shown that if you had a sample of Tritium, it takes about 12.3 years for half of the tritium to be decayed. For watch lume, that means that after 12.3 years, the lume will be ~1/2 as bright.
Photo Credit to the National Institutes for Quantum Science and Technologies
All of the details there aren’t terribly important. All you need to know is that Tritium is a radioactive isotope that shoots out an electron when it decays.
What’s With The Tubes?
You may be asking yourself questions like: So Tritium shoots off an electron after a while- so what? … and that is a great question! The overall idea with Tritium lume is two steps: get a stream of electron decay, and convert that into light. The first step is done by filling a tube with Tritium, as we have already learned. But how do we convert that into light?
Turns out, this is the easy part. Just as phosphorescent paint is used on normal lume, the same thing is done to convert the radiation to light. The same phosphorescent process occurs when electrons hit the paint. So if you line the inside of a Tritium container with lume, it will glow as long as the Tritium is decaying, which is many years. Of course, the phosphorescent paint can be fine-tuned to the circumstance and to the application, but the general idea is exactly the same.
Tritium lume in a dark environment.
Tritium is clear and bright in the dark, and tubes can even glow different colors!
Is It Safe?
Without fail, the best way to freak someone out is to say the word “radioactive.” But most people don’t know what the term even means. As we showed before, to be radioactive just means to be radiating a particle. In this case, it was a single electron. Being radioactive doesn’t really tell you anything about its safety. Some radioactive materials are safe and some are dangerous- you must specify material to know.
In our case, the Tritium’s decay is absorbed by the phosphorescent paint, and if somehow it didn’t (which is extremely unlikely), it would be blocked by the metal in your watch, and if somehow it wasn’t (which is even more unlikely), the amount of radiation is negligible.
“In human tissue, tritium’s beta particle cannot penetrate the typical thickness of the dead layer of skin that exists on the outside of the human body. For this reason, the beta particle emitted by tritium is generally only considered to be hazardous if a large quantity of tritium is, or has the potential to be, taken into the body by inhalation, skin absorption, and ingestion of tritiated water. Tritium mostly behaves just like ordinary water in the body, distributing equally throughout the body’s water and excreted in the same ways as water, such as in the forms of urine and sweat.“
-the Health Physics Society Specialists in Radiation Safety
In short, yes, it’s safe.
Conclusion
Tritium is like magic, even after you learn the science behind it. As an owner of a Tritium watch, it is always a delight looking down in the middle of the night and seeing it shine. It’s not just a fun gimmick- it really is the pinnacle of lume, and can be extremely practical for many folks who spend time outdoors or work a night. That being said, it is just a ton of fun if you don’t fit that category.
Another aspect of Tritium watches to consider is the physical size of the tubes. Since the tubes are a specific size, manufacturers have to design their dials to work around their thickness. It is always interesting to see how they incorporate the vials- sometimes they are hidden, and sometimes they themselves are used as markers, etc.
Go out and shop for Tritium watches with your new knowledge of the subject!
Don’t hesitate to comment below if there is anything that you’d like to better understand.
Social Plugin