How it functions

The Set Theory Clock, also known as the Berlin Clock, makes use of the principle of set theory to depict the time. The time of day is displayed in a 24-hour format and can be determined by simply adding and multiplying the glowing lights.

The first, uppermost row consists of 4 red lights, whereby each of these lights stands for 5 full hours. The 4 red lights in the second row display one full hour apiece. For example, if the first 2 lights in the uppermost row and all 4 lights in the second row are lit up, that represents 1400 hours, or 2 p.m. (2 × 5 + 4 hours). The third row is composed of 11 lights: 3 red and 8 yellow. Each light in this row stands for 5 elapsed minutes. The 3 red lights have been assigned to mark the quarters of an hour and are intended to make reading the clock easier. Last of all, the yellow row at the very bottom displays units of single minutes.

The current time ─ it is now hours ─ results from:

The round yellow light crowning the clock at the top is of minor significance for telling the time: It blinks every second.


Dieter Binninger, an inventor and tinkerer from Berlin who is also a trained clockmaker, designed the Set Theory Clock on behalf of the Berlin Senate in 1975. The clock was installed on Kurfürstendamm in the Berlin-Charlottenburg district and rapidly evolved into a tourist attraction, though it turned out to have one serious disadvantage: its inner workings consisted of hundreds of light bulbs, some of which constantly burned out. BZ, a local Berlin newspaper, sported the headline back then: “Ku-Damm clock can do a lot, except run”, which meant the clock had to be inspected and repaired on an ongoing basis. In the end, the costs for operation and upkeep were running EUR 5000 a year, and neither the city of Berlin nor the district of Charlottenburg wanted to bear the costs. For many a year the clock dozed on, more out of order than functioning, until 1995, 20 years after it had been installed, when it was shut off. The only reason the clock still exists to this day and has found a new location in front of the Europa Center complex is thanks to an initiative sponsored by businessmen at the center in Berlin.

Dieter Binninger tried to rectify the weak points in the construction design of his Set Theory Clock by developing a long-lasting light bulb, a so-called “perpetual light bulb”. His idea was to intensely reduce the power input of a standard commercial light bulb in order to drastically prolong its product life. Between 1980 and 1982 Binninger registered 3 patents for “Prolongation of the product life for all-round-usage light bulbs”, which basically came down to running the light bulb on undervoltage. Though a longer product life is achieved this way, the light bulb’s already low efficiency sinks even further at the same time; the prolonged product life has to be paid with increased costs for electricity.

Binninger indicates a mean product life of 150,000 hours for his long-lasting light bulb, whereby a standard commercial light bulb lasts merely 1000 to 2000 hours, along with an additional 50% higher power consumption. For a 100 watt light bulb, this means that additional power costs of around EUR 10 arise during the first 1000 hours in operation (at an electricity price of EUR 0.20 per kilowatt-hour), a sum much greater than the purchase price for a normal light bulb. Which is why Binninger’s method didn’t meet with much success, but it does continue to provide material for the wildest conspiracy theories to this day.

For More Information

The Wikipedia articles on the subject: “Set Theory Clock”, “Dieter Binninger”, “Perpetual light bulb” and “Incandescent light bulb”

Binninger’s patents (DE 2921864, DE 3001755 and DE 3213333) can be researched on DEPATISnet at DPMA, the German Patent and Trademark Office.

A fan of the Set Theory Clock tells of his encounter with Binninger: “Die Berlin-Uhr - Die Stunde schlägt nicht, sondern leuchtet!” (‘The Berlin Clock: The hour doesn’t toll, it lights up!’)

Models of the Berlin Clock produced by Binninger and a successor company turn up now and then at flea markets in Berlin and at ebay.

A tabletop version of the Set Theory Clock is currently being manufactured by the firm ASMETEC. (It’s a sure thing that the author of the Flash conversion would be happy to have their name mentioned)

“Fragen und Antworten” (‘Questions and Answers’) about the Berlin Clock.

My work is published under the terms of the Creative Commons 3.0 Lizenz. The Berlin Clock may be used freely for private and commercial purposes when indication of the author or a link to this website is made.