T Swiss Made T" or "Swiss T 25" : what does it mean ?

In order for timepieces to be read in the dark or diving under the sea, a luminescent material is laid on the dial indexes and hands.

Generally speaking, the emission of light is either of radioluminescent type (determined by the radioactivity of the material) or of photoluminescent type (determined by a exciting luminous radiation).

Timepieces featuring radioluminescent emission are mostly designed for very specific uses : military watches, professional divers watches, etc. In this case, the use of radioactive material is strictly defined by ISO 3157 Standard which allows only two types of radionucleides : tritium (3H) and promethium (147 Pm). It is important to specify that these radionucleides emit a radiation of low energy.

ISO 3157 Standard allows an optional marking for timepieces emitting less than a certain value. The marking may be made on the dial as follows :

deposits activated by tritium : T

deposits activated by promethium : Pm

On the other hand, timepieces with a higher value, such as divers' watches, must be marked as follows :

deposits activated by tritium : T 25

deposits activated by promethium : Pm 0,5

The indication "T Swiss made T" means that the watch is Swiss and contains a certain quantity of tritium that emits less than 227 MBq (7,5 mCi).

The indication "Swiss T<25" means that the watch is Swiss and contains a certain quantity of tritium that emits less than 925 MBq (25 mCi).

Most of the Swiss watches use a light emission of photoluminescent type. Some of them bear the optional marking "L Swiss Made L" to indicate it.

The light emitted by the hands and index of the dial is the radiation energy deposited in the luminescent crystals by alpha and/or beta particles. Next to no light is due to gamma rays.

Dial is made with Radioluminescent paint consisting of certain radioactive material mixed with a luminescent crystalline powder. The first radioactive material was radium-226 (Ra-226), but it hasn't been widely used.

Tritium (H-3) and promethium-147 (Pm-147) are the radionuclides of choice.

Other radionuclides have also been used such as strontium-90 (Sr-90) and carbon-14 (C-14).

Zinc sulfide powder has been the most widely used luminescent material.

TRITIUM

Tritium (H-3) is a low energy beta emitter with a 12.3 year half-life. It does not emit gamma rays.

So Rolex T<25 dial means it will last for 24.6 years only.

(less than 25 years!)

Luminova and then Superluminova were developed to avoid the use of any radioactive materials whatsoever. Their intent was to replace tritium lume outright.

Rolex Sports or Professional watches (except the Daytona) generally have <T25 and dress watches like the Date-Just are marked T Swiss T.

This is basically down to the amount of luminous material applied to the dial. The more paint, means more Tritium meaning more radiation as minimal as it is.

Swiss

Luminous Material Radium

Used until 1960

Radioactive

Swiss- T<25

Luminous Material Tritium

Used from 1960 -1998

Radioactive, Radioactivity less than 925 MBq (25 mCi)

T Swiss T

Luminous Material Tritium

Used from 1960 -1998

Radioactive, Radioactivity Less than 277mBq (7.5 mCi)

SWISS

Luminous Material Superluminova

Used from 1998 till 2000

Not Radioactive

SWISS MADE

Luminous Material Luminova (Green

Used from 2000

Not Radioactive

SWISS MADE

Luminous Material Chromalight (blue)

Used from approx. 2008
(introduced with DeepSea)

Not Radioactive

These are what I have researched and may not be all correct , however I hope this give a simple illustration on the type of Rolex Dial being used on your and my watch...

I hope it helps for one of my bog fans asking on this... So now you know T<25 dial on Submariner I always prefer for VR (Vintage Rolex) as all are made on the Golden Period of Rolex. 1960-1998.

HK Snob