Citizen’s Eco-Drive technology has spent half a century redefining one of the fundamental questions of watchmaking: where does a watch get its energy? For centuries, mechanical watches relied on wound springs. Then along came quartz watches, which brought great accuracy but introduced a new dependency in the form of battery changes.

Citizen’s engineers approached the problem differently: what if a watch could simply draw energy from the light around it? That question led, in 1976, to the launch of the Crystron Solar Cell, the world’s first light-powered analog watch and the beginning of what we now know as Eco-Drive.

1976: Crystron Solar Cell

The Crystron Solar Cell was far ahead of its time. At a time when the world was confronting an energy crisis and there was growing awareness of the need for sustainability, the concept offered a practical alternative. Over time, that early solar experiment would evolve into one of the defining pillars of Citizen’s watchmaking.

The principle behind Eco-Drive is deceptively simple. Light passes through a translucent dial and into a photovoltaic cell beneath. That light energy is converted into electricity and stored in a rechargeable cell, which powers the movement. Unlike early solar watches that required strong sunlight, Eco-Drive movements are designed to capture even faint indoor light, allowing the watch to run continuously in everyday conditions.

From that foundation, Citizen began a decades-long process of refining the technology. In 1986, improvements allowed Eco-Drive watches to achieve a running time of approximately eight days. By 1995, the introduction of a lithium secondary battery extended the run time dramatically, allowing the watch to run for six months on a single power reserve. At that point, solar power had become a practical everyday solution.

Citizen continued to push the concept further by combining Eco-Drive with new timekeeping technologies. In 1996 the brand developed the world’s first radio-controlled watch with light-powered technology. By receiving terrestrial time signals from atomic clocks and adjusting itself automatically, the watch eliminated two of the most common inconveniences in quartz ownership: battery changes and manual time setting.

1996: The world’s first Radio-Controlled model incorporating Eco-Drive

Over the following decades, Eco-Drive became the foundation for a series of increasingly sophisticated developments. In 2011, Citizen introduced Satellite Wave, taking the concept beyond land-based transmitters. By allowing the watch to receive signals directly from GPS satellites, it could automatically adjust the time virtually anywhere in the world. In 2016, the brand celebrated the 40th birthday of Eco-Drive with the launch of Eco-Drive One, featuring a movement just 1.00mm thick, at the time the world’s thinnest light-powered watch.

Citizen’s pursuit of precision reached a new level in 2019 with the introduction of Caliber 0100. With an astonishing accuracy of ±1 second per year, it became the most accurate light-powered analog watch ever produced. More recently, the Eco-Drive 365, launched in 2023, demonstrated another breakthrough: the ability to run for a full year on a single power reserve even when stored in total darkness.

2019: Citizen Caliber 0100

2023: Citizen Eco-Drive 365

2025: Citizen Promaster Dive E365

These developments show why Citizen is still the global leader in light-powered watch technology. For 50 years the brand has not simply made solar watches, it has continually expanded what light-powered timekeeping can achieve. Today Eco-Drive watches are worn in approximately 140 countries and regions worldwide, and they are one of the primary reasons collectors and everyday wearers choose Citizen.

The 50th anniversary of Eco-Drive is a fitting moment to reflect on that journey. To mark the milestone, the brand introduces the Eco-Drive PHOTON, a limited-edition model that reflects half a century of light-driven watchmaking.

Citizen Eco-Drive PHOTON

The name itself points directly to the concept at the heart of Eco-Drive. A photon is the fundamental unit of light energy, the smallest measurable packet of light. In this watch, Citizen translates that idea into a striking visual language that echoes the movement’s underlying function.

The dial design draws inspiration from the famous double-slit experiment, a landmark demonstration in the study of light. Two metal plates featuring ripple-like slits are layered over one another, creating a three-dimensional structure through which light passes. Beneath them sits a reflective dial surface that produces its vivid colors through microscopic structures that interact with light, rather than through traditional pigments. As light interacts with the dial through the slits, the surface shifts in tone and expression, giving the watch an ever-changing visual character.

The dial design draws inspiration from the famous double-slit experiment

Powering the Eco-Drive PHOTON is the new Caliber E036 movement, part of Citizen’s latest generation of light-powered calibres designed to maximize efficiency and extend running time to a full year on a single power reserve.

The watch has a 39.6mm case made from Citizen’s proprietary Super Titanium™, a material that combines lightness with scratch resistance through the brand’s Duratect surface hardening technology. The rounded octagonal case flows seamlessly into the bracelet, creating a cohesive and contemporary silhouette.

Two versions of the PHOTON will be produced, each limited to 5,000 pieces worldwide. One pairs a silver-toned case with a deep blue dial visible beneath the layered slit structure, accented by a yellow seconds hand, while the other has a bold black-and-gold configuration and a purple seconds hand. Both are engraved on the caseback with the Eco-Drive 50th Anniversary logo and an individual limited-edition number.

The Eco-Drive PHOTON captures the spirit that has driven Citizen’s innovation for half a century. Just as Eco-Drive technology transforms light into energy to keep time moving forward, the watch turns that same idea into a striking piece of design.

Fifty years after the launch of the Crystron Solar Cell, Citizen continues to show how light, one of the most abundant resources on Earth, can power the future of watchmaking.