Especially on sports watches, luminance is a vital design element: even when we are not diving in the depths of eternal submarine darkness

Some six years ago, I wanted to compare the luminosity of the non-radioactive SuperLuminova with that of the traditional tritium-activated phosphorus and conducted a small test, with the Ulysse Nardin Marine Diver being the the SuperLuminova candidate, and the classic IWC GST Aquatimer with its infamous tritium-SL-combination dial representing the other category. The outcome of the test was quite interesting:

ulyssenardin.watchprosite.com

During the following years, it has become a design trend to use not only the “classic”, greenish SuperLuminova as luminous substance on hour markers and hands, but to tint that in different colours. This permits a larger freedom in combining colours on watches and therefore offers a wider spectre of watch designs. Coloured SL is produced rather easily, since the the original state of SL is that of a fine granulate or powder, that is bound by liquid substance to be applied on dials and hands. Any colour pigments can be added to the SL granulate in order to achieve the desired effect. This can go so far as to add black pigments that result in a black marker or hand that glows in the darkness. Nemoto, the inventor company of SuperLuminova, and its main license partner in Switzerland, Tritec, offer a wide array of colours. Currently, the use of tinted SL became popular to simulate the appearance of old and yellowed phosphor on vintage timepieces.


However, this freedom of design comes at a price: the colour pigments reduce the intensity and duration of the SL’s phosphorescence. In the case of black-tinted SuperLuminova this even leads to nearly complete ineffectiveness, which raises the question why someone would spend the money for non-luminescent luminous mass?

Another development is that of a bright white SuperLuminova. The well-known SL that is used since 1993 is of a light green colour, with its current formula wearing the technical designation C3. Despite its high efficiency, the greenish tint is not popular among watch designers, since it is not a perfect contrast with most black watches, or blue dials. Therefore, the development of a bright white pigment, dubbed C1, was a real progress, and currently a majority of sports watches is equipped with this material. However, already the data sheets suggest a reduced phosphorescence intensity of C1, compared with that of C3.

Another aspect worth to be pointed out is that the colour pigments added to the SL only marginally influences the actual glowing colour. Basically, all kinds of SL are glowing in pale green, regardless of their appearance in daylight. There is only a very decent colour tint when such pigments were added to achieve, say, a bright blue or red SuperLuminova marker.

My new test should now reflect these new design trends, by comparing a watch with classic greenish C3 SL with others having white C1 and brightly coloured SL. Of course it would be perfect to have three watches of the same brand and line, with only the luminous material being the difference. However, my choice is limited to those watches I have in my possession, so I have to combine different brands.

Obvious candidate for the C3 fraction, and unbeaten “master of glow” in my collection since more than ten years is still the Marine Diver by Ulysse Nardin. Up to now, I had no watch that could really compete with the intensity and duration of its luminescence.


In this context it is necessary to point out that, despite the use of identical SuperLuminova materials, there are many other factors influencing its efficiency: the purity of the granulate, its sealing against humidity, the thickness of application, the type and colour of its base, and some others. Consequently, it is not only possible, but rather probable to find two different watches with the same SuperLuminova equipment to perform very different in the luminescence category.


That Ulysse Nardin lent me a very new and rubberised special model of the Marine Diver, the “Red Sea”, was a fortunate opportunity, since it has the same hand and hour marker design as my older watch, but sports an all-over bright red SL equipment, offering a perfect comparison candidate.


Finally, my nice Tissot PRC 100 chronograph with its bright white C1 SuperLuminova completes the trio.


Since I did not yet have night shots of two other “retro-design” sports watches, I added these as well: the well-known Legend Diver by Longines, and the large Breitling SuperOcean Heritage, both equipped with C3 on hands and markers. These two eventually allowed another interesting conclusion.



Testing Procedure:

For a good “charge” of the luminous elements, I placed the watches in very bright sunlight, since the strontium aluminate in SuperLuminova is said to be best charged by the visible spectrum of daylight. I considered two hours to be enough. Then I brought the watches into a window-less room in my house’s basement, where I had already prepared my camera on a tripod.

I had planned to keep the exposure values preset on the camera the same, throughout the whole series. This should cover about six hours, with pictures being made shortly after the daylight exposure, an hour afterwards, a further two hours later, and finally after six hours. The automatic white-balance on the camera was changed to a daylight preset, since otherwise the colour of the glow would change in every picture.

Since my 60mm macro lens on a camera with APS-C sensor corresponds to roughly 100mm on a full format sensor camera, the working distance between the watches and the camera was rather large, about forty centimeters. Consequently, the intensity of light recorded by the sensor was much lower than it had been in my experiment conducted six years ago, due to the much larger distance. Thus it does not make sense to compare the new test pictures with those in my earlier article.

To my shame I have to admit not having read my own article before conducting my new test. Otherwise I would have been warned about the massive drop of glow intensity already within the first hour, and used a camera setting that maximises the light recording. Instead, I repeated the same mistake of six years ago, and realized that my initial camera setting, that brought the most satisfactory pictures of the “fully charged” watches, resulted in near-complete darkness on the pics only an hour later.


As a matter of fact, SuperLuminova’s afterglow luminance is reduced to about 6% of its original value within 60 minutes.


Therefore, I decided to recharge the watches with the light of two halogen working lights for about twenty minutes and to repeat the initial shot, showing the watches at full charge, but with the same camera settings used for the shots at 1, 3 and 6 hours. This explains the display of the wrong time on the first picture.


Test results:

I think the pictures to be rather self-explanatory. Please keep in mind that the depiction of the glowing watches strongly depends on your individual monitor settings, especially the gamma value. While some might not see any luminescence on the later pictures, others might see the markers and hands much more clearly. It is the relative luminescence intensity, compared within the watches, that counts. The text in the pictures will also help, since its colour is picked from the “Red Sea’s” glow in the first picture, and kept the same throughout the whole series. A dark background on the monitor would be perfect, but our forum software only offers a bright white which kind of outshines the faint glow of the watches in the pictures.


The most apparent test result is that neither the coloured SuperLuminova, nor the bright white C1 SL are matching the efficiency of the older C3 SL on the standard Marine Diver. Especially the colour tinted SL of the “Red Sea”, while equally lavishly used on hands and markers, is just barely visible after only 1.25 hours of darkness, the later pictures (3.25 and 6 hours) only show darkness at its position (bright monitor setting will show a very faint impression of the watch being there, though). The white C1 SuperLuminova of the Tissot is only marginally better.


The conclusion is that if you search a watch with optimum night visibility, make sure to choose a watch with the greenish C3 SuperLuminova, instead of the more fashionable white or colour-tinted substances.


What about tritium?

However, I have to add a certain reservation to this statement: While SuperLuminova is the most frequently used luminescent agent on watches, it is not the only one. A highly interesting alternative is the “Permanent Light Technology (PLT)”, developed by the Swiss manufacturer MB microtec AG. The system consists of tiny crystal glass tubes, coated with phosphorescent zinc sulfide on the inner side, and filled with pure tritium in gaseous state. Unlike the older, now forbidden phosphorus-tritium granulate used for decades on watch dials and hands, Microtec’s system assures that no radioactivity is leaving the glass tubes, and also the glowing efficiency of the luminous substance is much higher and more stable, mostly due to the high pressure of the gas in the tubes. These attributes made the PLT a perfect supplier for the watches of the US military, with the watches being produced under the brand name Traser. Tritium gas tubes are available in different colours, too, but like the coloured Luminova material, these are nowhere as bright as the pure, greenish tubes.

However, PLT is suffering from two disadvantages: the first is a limitation for the watch design, since the small tritium tubes (with only 0.5mm in diameter, in lengths from 1.3 to 6.6mm) that can be used in wristwatches are produced in cylindrical shape only and therefore watch designers have to tweak their drafts considerably, to accommodate the tubes in their numerical markers or classically shaped hands, for example.

The second limitation lies in the tritium’s nature as radioactive substance. By constantly emitting energy, tritium transforms into helium. After 12.3. years, 50% of the tritium has made this transition and ceased to be an activator for the luminous substance. After another 12.3. years, a further 25% of the original tritium amount is inactive. Consequently, the luminescence intensity of tritium tubes is reduced by roughly 10% each year. Since the tubes are highly standardized, most watch manufacturers using them guarantee a steady supply of fresh tubes that can be exchanged for the old ones.

Most Traser watches are equipped with quartz movements, but there is a brand offering interesting mechanical watches with tritium tubes, Ball. Unfortunately, Ball is distributed neither in Germany nor in Austria; I would have liked to get my hands on one for a test, but this will have to wait.

According to MB microtec, the tritium tubes are glowing considerably brighter than SuperLuminova already after a minute of darkness, with no measurable intensity reduction, aside the natural deterioration due to the radioactive material’s half time.


And the other two watches?

Finally, a few words should be dedicated to the last two watches of my small test: the Longines and the Breitling. Both are equipped with the same C3 SuperLuminova, and yet there is a distinct difference in the intensity of their glow already after an hour of darkness. the main reason for this presumably lies in the care of the C3’s application: The Breitling has small luminous dots near the hourmarkers, all of them being domed rather high placed on bases made from white lacquer. The latter perfectly enhances the glow.


The Legend Diver, on the other hand, has thinner, less evenly shaped strips of SL applied to the dial. While they also have a white base, this seems to be less smooth and shiny than that of the Breitling’s markers.


This makes the difference between the two watches. Apparently, also the hands are differently treated with SL, since the Superocean’s hands are a lot brighter as well.

And in another six years? Who knows which enlightenment technology will come next? LEDs powered by a micro-generator charged by the winding rotor? We’ll see, in my next test - 2018.

Finally, let me quote my own article from 2006: “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?”

Copyright June 2012 - Marcus Hanke & PuristSPro.com - all rights reserved

PuristSPro Homepage | ThePuristS Homepage

 
This message has been edited by Marcus Hanke on 2012-06-14 15:08:44 This message has been edited by AndrewD on 2012-06-21 19:26:34