Ulysse Nardin

The first 'scientific' luminosity test! (long and fascinating!! - :-D) ...

 

Among the various bestsellers of standing quotations about the qualities of watches we always find "glows like a flashlight!", "shines brightly through all the night!", and "highest luminosity under all conditions!". Sometimes, these statements are supported by digital pictures of watches shining like a nuclear burning element. impressive, very impressive this is.

I have to admit, that I, too, was prone to such enthusiasm. And, like most other "watch newbies", I loved to hold my new diver/pilot watch before my eyes after going to bed, enjoying the brightly glowing markers, hands and numerals. And of course I was happy, and firmly convinced of my watch's superior qualities, when I could still read the time when waking up after several hours of sleep. Wonderful watch! glows like a flashlight all the night!

Meanwhile, I have become a bit more sceptical, but never really made the step towards a test under 'scientific', that means reproducable conditions. The time came when I finally acquired a watch that I always liked, but which came out second after the UN Marine Diver when I had to decide between these two: the IWC GST Aquatimer.

Back then, the Aquatimer was a bit too professional in appearance for my taste. In my eyes, this impression has not changed, but now I already have the Marine Diver since more than four years, so the path was free to add the Aquatimer to my small collection. Additionally, this model has been discontinued by IWC nearly two years ago, and I somewhow disliked the more conventional successor. So it was a quick decision when I found a steel GST Aquatimer at a dealer.

As it turned out, this was a quite early model, which had been equipped with a unique (and somehow weird) mixture of tritium-charged phosphorus and non-active Super Luminova as luminous elements on the dials and hands. Apparently, the IWC engineers did not trust the then new Super Luminova material and decided to use tritium on the more vital elements: the hands, the 12 o'clock marker and the index point on the diving bezel. Later, when the use of radioactive materials in watches was generally discontinued, these elements, too, got the same Super Luminova as the other hour markers.

The UN Marine Diver never had tritium as luminous material, but was launched with full SL equipment. Immediately, it shined out all my other watches, and until now, it still is my absolute reference regarding luminosity.

Consequently, my little luminosity test was executed. These were the conditions:

I placed both watches directly under two equally strong lamps (100 watts) for five minutes. Then I quickly brought them into my absolutely dark bathroom (no windows), where the camera was waiting, pre-focussed on the spot where the watches were to be placed side-by-side.

The camera used is a Casio Exilim EX-P 600, a mid-range compact camera, that allows all settings to be made manually: aperture, exposure time and focus. This was essential to offer a constant that is necessary to be a base for the comparison.

As a time frame for the experiment I chose six hours, which is an average night's sleep, and I would make an additional picture after 3 hours, to illustrate the changes in luminosity. Between the shots, the watches were stored in absolute darkness.

After some initial test pictures, I determined the following setting to work well: aperture 4.0 (to offer at least a rudimentary depth-of-field), an exposure time of 10 seconds, and an ASA setting of 100 (this camera introduces substantial grain already at ASA 200, with ASA 400 being really bad, so I wanted to keep the picture quality of ASA 100).

The first shot was promising:

Note that the camera's sensor and software is interpreting the colours of the brightly shining elements differently, almost every time. In reality, the colour is not as blueish as shown here (which would be quite correct for the UN Blue Wave, though).

However, three hours later I realized I had been far too optimistic when anticipating the luminescent material's capabilities. When I entered the improvised photo studio, with my eyes being used to daylight, I saw nothing of the watches. Only after a long time, the eyesight adapted itself to the darkness, and I could read the watches. The camera sensor, though, was not so good:



You see exactly -- nothing. nada. nix. Already within three hours, the light emitted of the two watches became so faint that the camera settings were insufficient to record any information on the sensor.

Instead of repeating the whole experiment, I decided to restart at the current 3 hours-status this time making use of all reserves the small camera offers, except the ASA: The aperture was fully opened, to f 2.8, and the exposure time was set to 1 minute. And after the full six hours had passed, I redid the 0 minutes-shot with these settings, after having placed the watches under the lamps for five minutes again.



The light emitted from the UN Marine Diver's markers and hands is bright enough to illuminate the whole dial at this setting, even the words printed on it can be read. Very interesting to see the difference in luminosity and colour of the Aquatimer's elements: The Super Luminova hourmarkers are shining brightly, whereas the tritium hands and the dot on the bezel are darker. Weirdly, the 12 o'clock marker is barely visible at all, when it should be stronger than the other markers.

Three hours later:



While the Marine Diver's dislay can still be read without too many difficulties, the dramatic decrease of the light emission is evident, if you compare it with the letters of the text written into the pic - these texts have the same colour and brightness on all pics. The UN's bezel dot is substantially weaker, indicating that there is less SL material than on the dial markers. In the center of the hands is a dropoff of luminosity as well. This is not evident to the human eye, but the camera sensor shows it clearly. The reason is that the hands are completely skeletonized, to keep the mass - and thus the inertia effects on the movement - as low as possible. The Super Luminova is then applied into the hole. It is impossible to get a 100% evenly thick amount of SL there, and already tiny differences will result in different light emission values.

The IWC Aquatimer is looking rather bad - especially, when considering that it is a sports watch, which should offer a maximum legibility under all lighting conditions. The Super Luminova hour markers are completely dark, while - with some effort - the tritium elements can still be noticed. A dark monitor background would help here. Note, that the human eye, trained to the darkness, would not have difficulties to even recognize the Aquatimer's hour markers.



After six hours, the Marine Diver's luminosity has decreased further, while the Aquatimer's tritium parts have kept the brightness they already had three hours ago. Due to their physical principle, they would stay on this level, even when the watch is kept in a dark place. Wehreas the Super Luminova parts' light emission would fade to zero within a day, or even less.

What are the conclusions to be drawn from this little experiment:

1) "Bright as a flashlight for all the night long!" - No, sorry. this does not exist. If it would, it would be a serious cause for concern, because, most probably, the luminous material of the watch in this case would be plutonium, not tritium - or SL. Even so-called sports or diving watches face a dramatic drop of light emission.

2) Never underestimate human biologics. Whenever we are happy to read the time on our luminous watches at 5 o'clock in the night, we should thank your eyes, and their amazing capability to adapt to even worst lighting conditions; not the watches.

3) IWC was right: The IWC engineers rightfully mistrusted the Super Luminova on the markers, since - after initial brightness - they fade away very quickly. The tritium elements (bezel dot, 12 o'clock marker, hands), while appearing very dim in the beginning, compared with the hour markers, retain their brightness, making them a safe indicator. the problem, though, is that tritium has a half-time of 11 years. After this time, its energy emission has dropped to 50% of its orignal value, which means that its capability to 'charge' the luminous phosphorus will also get smaller. In another 11 years, this emission has dropped to 25%, after 33 years it is 12.5%, and so on.

4) IWC was wrong: Ulysse Nardin shows that it is possible to create Super Luminova dials and hands that retain a fully satisfactory brightness for more than six hours, fulfilling 99.99% of the practical needs (only if you are a cave explorer without any electrical light, or living in a polar winter, then you will have problems). The key factor lies in the way Super Luminova is applied. Brightness and endurance depend on how fine the SL grain used on the dial is, and especially on the thickness of the SL markers. The SL is applied in several layers, each of them bound by a special glue. The thicker, the brighter and longer. Another factor is the base colour. If SL is applied on a dark background, this will shine through a thinner SL layer, and compromise the luminosity. Best effects therefore are to be expected with white or silver dials. Good dial manufacturers will at least leave white base areas on black dials for the SL application. Finally, the purity of the SL granulate is also important. With colour pigments, luminous markers with nice and fashionalbe colours can be made. But these pigments reduce the luminosity. This is why the Blue Wave with its nice blue SL is less bright than a standard Marine Diver.

If you have succeeded in reading all the way down until here, you will agree with me how fascinating it is that someone can spend so many words on such a minuscule detail. Oh watch enthusiasts - aren't they crazy?

Best regards,
Marcus

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