Why does the moon glow? Why is it that a lifeless sphere of dark grey rock shines in our night sky? These are questions that not many think about, but they perhaps deserves a bit more illumination (see what I did there?).
Full moon (photo courtesy Wikipedia)
The moon emanates no light of its own since it is geologically inactive and has no light-emitting materials on its surface. It does give off radiation that it has absorbed from the cosmos (mainly the sun), which isn’t visible to the naked eye. What we need to turn to is the moon’s visual albedo, the coefficient of reflection for the surface. The moon glows because it reflects light from the sun, something it does rather poorly I might add.
Geometric (or visual) albedo is the fraction of light that the surface (in our case the moon) reflects back in all directions. A perfect reflector would an albedo of one, meaning that 100 percent of the light is reflected back; a body that reflects no light at all would have an albedo of zero. In reality, no surfaces ever have albedos of exactly zero or one; all fall somewhere in between.
The moon, with a visual albedo of 0.12, is less reflective than the green grass in your yard, which has an average of 0.15.
The number fluctuates based on the phase of the moon, but it is a rather dim light in the sky compared to other things. If we had another planet earth in the same spot as the moon, that earth, with its 0.37 average visual albedo, would appear 100 times brighter in the night sky.
Hypothetical earthshine on a new moon
Even more interestingly, the glow from the moon isn’t made entirely of light reflected from the sun. It is partially made of earthshine (light reflected off the earth’s surface), which is first reflected off the moon, then off the earth, and then back off the moon again. The best way to see this effect is at or near new moon when you can faintly see the portion of the moon that is in shadow even when the sun is shining on the opposite side.
The glow from the moon comes from multiple sources, varying due to solar fluctuations, orbital positions, and the topography and fluctuating weather patterns on earth. Still, the glow remains and is a nearly constant feature of our nocturnal experience.
This glow has inspired artists, musicians, and writers throughout history. And now it has inspired some of the greatest watchmakers of our age to create a moon that glows of light it has absorbed from the world around it.
One such moon can be found on the A. Lange & Söhne Grande Lange 1 Moonphase Lumen.
A. Lange & Söhne Grande Lange 1 Moonphase Lumen
And, boy, does it glow!
A. Lange & Söhne Grande Lange 1 Moonphase Lumen glowing in the dark
The next departure
The Grande Lange 1 Moonphase Lumen is the third departure from the iconic classicism that defines A. Lange & Söhne. Some might argue the Zeitwerk was a departure, but that model still maintains a good grasp on the design values underlying all A. Lange & Söhne models.
Instead, the first two leaps from the expected came with the addition of luminous materials, something unfamiliar to other models in the A. Lange & Söhne lineup.
A selection of “black” watches by A. Lange & Söhne including the Grande Lange 1 Lumen (second from left) and the Zeitwerk Luminous (at top)
First there was the Zeitwerk “Luminous” (no surprise that this model would be first) with lume applied to the digital time disks and a transparent dial that allowed the hidden portions of the disks to be charged at all times.
This gave way to the next departure: the Grande Lange 1 Lumen. This piece featured a similar transparent dial that allowed the outsized date disks to be charged, but also added luminous material to the hour, minute and second hands, the hour numerals and markers, and the power reserve hand and scale.
This watch represented the most lume A. Lange & Söhne ever added to a timepiece.
Until now.
A. Lange & Söhne Grande Lange 1 Moonphase Lumen
The third departure from the brand’s classic form is the Grande Lange 1 Moonphase Lumen, which is literally a depiction of the night sky on your wrist. It retains the same locations of luminous material from the Grande Lange 1 Lumen while adding the moon phase disk with 1,164 stars and a stunning representation of the moon.
Arch of the Milky Way taken from Paranal, Chile (photo courtesy Bruno Gilli/ESO www.eso.org/public/images/milkyway/)
This piece shines just like the universe, if the universe was small enough to fit into your pocket.
A. Lange & Söhne Grande Lange 1 Moonphase Lumen glowing in the dark
Special considerations
The most incredible aspect of this watch is how it deals with recharging the luminous coating on the date and moon phase disks.
It all begins with a little science lesson in light.
A. Lange & Söhne Grande Lange 1 Moonphase Lumen glowing in the dark
Light is a combination of different wavelengths of visible energy radiation. Sunlight consists of infrared, visible light, ultraviolet, x-rays, and radio waves, though some of this energy is dissipated by the earth’s atmosphere.
That is a great thing as ultraviolet light is made up of three smaller wavelengths, or subtypes, called UVA, UVB, and UVC, of which UVB and UVC are rather harmful to the human body. UVC is almost completely absorbed by the atmosphere and pretty much never reaches the ground, but UVB is lower in energy and is able to make it through, damaging our skin and eyes as a result.
Subtypes of ultraviolet radiation (table courtesy Wikipedia)
UVB has a wavelength between 280 and 315 nanometers (.28-.315 microns) while UVA has a wavelength between 315 and 400 nanometers (.315-.4 microns), which spans the gap between UVB and the visible spectrum that you and I can see. Visible light uses the wavelengths between 400 and 700 nanometers and contains all the beautiful colors of the rainbow.
But why on earth am I telling you all these numbers that clearly represent nerd-speak for boring?
A. Lange & Söhne Grande Lange 1 Moonphase Lumen glowing in the dark
Because this is the information that makes the Grande Lange 1 Moonphase Lumen entirely possible, and it needed to be fully understood and considered by the designers and engineers at A. Lange & Söhne.
A. Lange & Söhne Grande Lange 1 Moonphase Lumen glowing in the dark
How it works
The luminous coating that has been applied to the date and moon phase disks absorbs UV light that it slowly re-emits over time. This process of re-emission is actually very, very complicated and utilizes “forbidden” – meaning how energy changes energy levels in atomic nuclei – energy state transitions in quantum mechanics (which definitely makes it a topic for another day). The important fact is that the luminous coating must be exposed to UV light rather than visible light in order to be “charged.”
Important consideration number one: utilizing sapphire crystal and its properties. Normal silicate-based glass (used in car windows and the like) actually blocks a majority of UVB light, though it still allows UVA to pass through. For normal glass the transmission abruptly stops for wavelengths between 300 and 400 nanometers, beginning around 90 percent transmission at 400 nanometers and falling to zero by the time the wavelength reaches 300 nanometers. Based on the nerdy numbers I discussed before, it could mean trouble if a mineral crystal had been used.
A. Lange & Söhne Grande Lange 1 Moonphase Lumen
But, luckily, sapphire crystal transmits UV light very differently, allowing between 80 and 90 percent of UVB and UVA light to pass through, and if it was present, even UVC light. It holds this transmission well past the 280-nanometer wavelength of UVB light.
Clearly, it is fortuitous for the watch industry that sapphire crystal is already so widely used for strength and scratch resistance, since it also lets through all the UV wavelengths needed to charge luminous coating.
Important consideration number two: coating the sapphire crystal with a material that partially blocks visible light yet transmits UV light. This is the crux of the issue, and the savior as well. Since the disks need to be luminescent immediately upon changing to the next position, but the entire disks need to be somewhat hidden and provide no additional glow, a special coating was added to the sapphire crystal dial.
This coating blocks a decent amount of the visible light between the 400-700 nanometer wavelengths, similar to how sunglasses might, but this coating does something your sunglasses don’t, or shouldn’t: completely allow wavelengths under 400 nanometers to pass through – namely, UV light.
The result is a luminous coating that, thanks to the sapphire crystal dial and a transparent-to-UV-light coating, can be fully charged and yet still hide the resulting glow from view until the indication switches into the date window.
A. Lange & Söhne Grande Lange 1 Moonphase Lumen
The disks and the moon
The date window displays the tens numeral of the date disk with an applied luminous coating, and the single-unit disk, which is also made from sapphire crystal, allows for a stationary luminous background to glow through from behind.
That idea, combined with the technically advanced sapphire crystal dial, is what makes the incredible moon phase possible.
A. Lange & Söhne Grande Lange 1 Moonphase Lumen
The moon phase disk, which includes a depiction of stars, the Milky Way, and two moons, is a sapphire crystal disk that has been coated with the same material the dial has been coated with. Underneath the moon phase disk is a stationary background with a luminous coating that allows the night sky to glow. The coating on the moon phase disk allows the background lume to be fully charged at all times thanks to its transmission of UV light, but that doesn’t tell us where the moon, stars, and entire galaxy come from.
A. Lange & Söhne Grande Lange 1 Moonphase Lumen
These details are actually very precisely etched into the UV-transparent coating with a very tiny high-precision laser. This burns away the coating on the sapphire crystal disk and creates shapes where the luminous material can shine through without being blocked by the visible light-blocking coating.
Thanks to this method, the moon phase disk can glow at all times while allowing the phase to change at will.
A. Lange & Söhne Grande Lange 1 Moonphase Lumen
The rest of the dial is made opaque thanks to the blackened silver subdials and dial edging that helps to increase the visual effect of the lume. This third step in the exploration, with its glowing details and very technical coatings, has produced a truly inspiring watch; one that almost begs its owner to sit in a dark corner so that its beauty can be appreciated.
A close look at the movement side of the A. Lange & Söhne Grande Lange 1 Moonphase Lumen
For my hopes to be blessed, this Lumen edition will not be the last, and future editions should (if I may request) include the Langematik or Datograph Perpetual, and if we are truly lucky, the Richard Lange Perpetual Calendar Terraluna, which would present huge possibilities for the addition of these techniques.
I’ll keep all of my fingers and toes crossed for that one!
The Grande Lange 1 Moonphase Lumen is a spectacular watch, something that deserves many hours of star gazing (even if those stars are incredibly tiny). Make sure you take a look back at the Zeitwerk Luminous and the Grande Lange 1 Lumen editions as well to fully appreciate the ideas these watches explore in all of their A. Lange & Söhne glory.
A. Lange & Söhne Grande Lange 1 Moonphase Lumen
But while we wait for the next incredible editions, let’s break this one down!
- Wowza Factor * 9.75 Holy cow, the amount of lume and the technology behind the dials is definitely a huge wowza factor!
- Late Night Lust Appeal * 101.01 » 990.57 m/s2 If there was ever a watch more suited to lusting after late at night, I do not know of it. It begs for your midnight musings . . .
- M.G.R. * 65.9 Any A. Lange & Söhne caliber is already über geeky, and one with this type of outsized date, moon phase, and visible mechanics all with added lume, well, it’s a special kind of special.
- Added-Functionitis * Moderate/Severe Moon phase, date, and power reserve move this watch into the “pretty darn complicated” family, creating a need for extra strength Gotta-HAVE-That cream for the illuminating swelling.
- Ouch Outline * 11.02 Moving Old Oak Boards & Getting A Huge Splinter! This just makes me shiver because it has happened too many times in my life. You would think I would learn just to use gloves, but nope. Of course, if it meant I could get this puppy on my wrist for a while, I would gladly handle that wood all day!
- Mermaid Moment * It Glows!! I cannot imagine a world in which any single person would look at this watch and not immediately fall in love. If such a world exists, I hope I do not live in it, or at least that the ceremony would convince the non-believers in true love.
- Awesome Total * 1,066 Multiply the number of components in the incredible movement (446) with the number of extra layers of sapphire crystal for glowing purposes (3) and from the result subtract the number in the limited edition (200) followed by the hours of power reserve (72) to get a glowingly awesome total!
A. Lange & Söhne Grande Lange 1 Moonphase Lumen
For more information, please visit www.alange-soehne.com/grand-lange-1-moon-phase-lumen.
Quick Facts A. Lange & Söhne Grand Lange 1 Moon Phase Lumen
Case: 41 x 9.5 mm, platinum
Movement: manually wound A. Lange & Söhne Caliber L095.4
Functions: hours, minutes, seconds, large date; moon phase, power reserve
Limitation: 200 pieces
Price: €69,000
Trackbacks & Pingbacks
-
[…] As long as we are talking about materials, how about a material that lights up the night? That’s right, everyone’s favorite topic, luminant. In this case, we have Joshua Munchow giving us yet another excellent technical dive on the topic, specifically as how it relates to the A. Lange & Söhne Grande Lange 1 Moonphase Lumen (which was an impressive watch even before the knowledge dump). Of the more curious facts I learned, I was surprised to discover that our lawns are actually more reflective than the surface of the moon. Professor Munchow also gives us a lesson on light (specifically ultaviolet wavelengths), and well as explaining how Lange built the watch to let all the glowy bits get charged up. If you have not read one of his articles, you really owe it to yourself to check this out over at Quill & Pad. […]
-
[…] may remember a bit about that from my A. Lange & Söhne Grande Lange 1 Moonphase Lumen article last […]
Leave a Reply
Want to join the discussion?Feel free to contribute!
Wow. Great write up about a great watch. I will admit that I am a lume freak and not ashamed. This watch fixes the problem of many high-end watches I see showcased on blogs. They become useless after the lights go down. I like how L&S is heading into a new direction and using uber science to make it work. Fascinating…