German haute horology brand A. Lange & Söhne has launched the fourth watch in its Lumen range – the Datograph Up/ Down Lumen. Featuring a semi-transparent dial and a unique luminous display, the chronograph – with flyback function, jumping minute counter and power-reserve indicator – comes in a limited edition of 200 watches.

This is the fourth model in the Lumen range

Lange first introduced the Lumen in the Zeitwerk range in 2010. Since then, the Grand Lange 1 ( in 2013) and the Grande Lange 1 Moonphase (2016) have been subject to the “Lumen” treatment. These open dial watches with its distinct use of luminescent material really stand out in the Lange catalogue.

The watch is cased in 41 mm wide platinum

“A chronograph in the Lumen line seemed like a natural progression after the big date and the moonphase,” said Anthony Haas, director of product development at the German maison. “The great thing about these watches give our classically-inclined watches a more modern look.”

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The watch, cased in platinum like all watches in the Lumen range, is 41 mm wide and 13.4 mm thick. The case has two rectangular pushers on the crown side for operating the chronograph and one rapid correction pusher for the outsize date. The exhibition caseback offers users a peek into the lavishly-finished manufacture movement, more on that later.

A different character emerges when darkness sets in

However, it’s the dial that holds all of this watch’s appeal. Launched in 1999, the Datograph is as much a Lange icon as the emblematic Lange 1 model that put the Teutonic brand back on the haute horology map in 1994. The Datograph Up/Down with the characteristic power reserve indicator was launched in 2012.

What is striking about the Datograph is the sense of harmony that the designers have achieved on the dial. The characteristic outsize-date display marks the tip of an equilateral triangle, whose baseline is defined by the two counters for the seconds and the minutes. However, once darkness sets in, this Datograph reveals a whole new character.

The semi-transparent dial allows UV light to pass through

For in the dark, a green glow emanates from the sub-dials, the date display, the outer ring that houses the tachymeter scale and the minute scale subdivided into fifth-of-a-second graduations. The central chronograph hands, the white-gold hands that indicate time also emit this green glow.

This mesmerizing effect on the dial is thanks to the use of a semi-transparent dial and the generous application of SuperLuminova. The glass dial was developed in collaboration with a technical institute in Dresden and has been used in all the Lumen models.

Caliber L.951.7 in all its glory

“A glass dial in a watch is not the easiest to work with – we subject the glass dials to the same standard tests as the other. This is the Datograph, so there are two sub-dials and oversized date windows to contend with as well; so in the end you have a big glass plate with a lot of openings or cut-outs. The challenge was to develop a stable dial which you can wear every day,” said Haas.  

The semi-transparent dial allows for sunlight to charge the luminescent material beneath. A special coating on the semi-transparent sapphire-crystal dial filters out most of the visible light, but not that part of the UV spectrum needed to charge the luminous pigments. The darker the surrounding, the more clearly the displays contrast against the dark background. Even during the day, the semi-opaque dial allows for the entire mechanism to be clearly visible.

A closer look at the movement

But wait, there’s another party trick. The outsize date is designed to glow after midnight when the date changes instantaneously. This is made possible with a luminous tens cross (the outsize date consists of two separate display elements: the units disc and the tens cross) and a black printed units disc made of transparent glass which rotates above a luminous background.

The tens cross is exposed to UV light now

The sapphire-crystal caseback is a purist’s delight for it exposes the impressive beauty of the lavishly finished 454-part manually wound calibre L951.7. The tens cross is covered by a bridge in the standard Datograph Up/ Down movement. The bridge had to be removed to allow for light to hit the tens cross and units disc so that the luminous coating could be charged.

The 2.5 Hz movement has a power reserve of 60 hours and can allow time measurements of up to one-fifth of a second. The jumping minute counter of the chronograph advances by one marker exactly when the chronograph sweep-seconds hand passes the 60th second, even if the time measurement is stopped at that very moment.

The 41 mm dial sits well on the wrist

Available in a limited edition of just 200 watches, the platinum case is worn on a black alligator leather strap with a platinum prong buckle and is priced at AED369,000 (Approx. $100,500).