Seiko & Citizen Watch Forum Message Archive

Question: From Roger-san

About two months ago I purchased a new Seiko 1000 meter diver's watch. I love this watch! To me this watch has great character and I have worn it daily since I received it.

I have heard that the watch uses a soft iron cage inside the case to protect the movement from magnetic fields. Could Tokunaga-san tell me the strength of the magnetic field this watch is rated to resist. Also I am interested in knowing what the luminous material on the dial is. What does it contain? Is it Luminova or tritium?

Reply:

The magnetic-resistance as a diver's watch in the International Standard is 4800 or more A/m in a direct-current magnetic field. The magnetic-resistance of Seiko 1000m diver's has the ability of about 3 times up-grade of the standard. (Let's do this talk some day!)

About the luminous paints of Seiko watches, "Radioactive luminous paint" which uses a radioactive material was abolished five years ago in all watches including the diver's watches. We had switched to non-radioactive "Photo-luminescent paint" with high safety extensively.

The "Radioactive luminous paint" which was being used in Seiko watches before was not "Tritium" but "Promethium = ¹⁴⁷ Pm". Since the quantity of the radioactive material which can be used for one watch is restricted and radiation energy decreases, in the case of the watch used around 10 years, energy will become weak and luminous paint will not shine.

The "Photo-luminescent paint" of Seiko watches is called "LUMIBRITE" (trademark), and is made of SrAl ₂ O ₄ + Eu + Dy. We can use it without any restriction, excluding the above dangerous radioactive materials at all, and it can continue shining several hours and the most important feature of this luminous paint is safety for the users. Although the old photo-luminescent paint disappeared for a short time, in case of "LUMIBRITE", when it shifts to darkness from a general living environment (conditions which light hits for 10 minutes in the illumination of about 500 lx), it will shine for about 3 to 5 hours by after glow of light in case of general grade "LUMIBRITE", and in case of the highly efficient "LUMIBRITE" used for diver's watches and adventure watches etc., it will shine for about 5 to 8 hours in darkness. If even light has hit, long periods of use can be performed repeatedly any number of times, and there is little degradation in this paint, therefore "LUMIBRITE" is an excellent luminous paint for watches. (See the following figure).

Ikuo Tokunaga

Comparison of the luminous paints

SEIKO Professional 1000m

Some wishes to you who ask a question to Tokunaga.

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