Citizen Eco-Drive: how a light-powered watch works

A Citizen Eco-Drive watch runs on light. Light passes through the dial, the solar cell beneath converts it into electricity, and the energy is stored inside the watch to move the hands. Regular battery changes are not needed. In this article, we explain how quickly the watch charges, how to tell when it needs light, what to do if it stops and how to choose a suitable model.

We introduced Citizen and Eco-Drive technology more generally in the article Citizen watches: Eco-Drive, automatic and titanium.

How does light charge the watch?

In 1976, Citizen launched the world’s first light-powered analogue watch. Citizen introduced the Eco-Drive name in 1994. The principle remains the same:

1. Light passes through the dial.
2. The solar cell, located beneath the dial in many models, converts light into electrical energy.
3. The energy is stored in the watch’s rechargeable battery.
4. The stored energy powers a motor, which in turn moves the hands.

For this to work, the dial must let light through. According to Citizen, an Eco-Drive with an opaque dial could not generate electricity. Yet the dial cannot be completely transparent, as this would reveal the solar cell. Eco-Drive dials are therefore designed to let light through while keeping the cell hidden. In some models (Ring Solar), the solar cell forms a ring around the edge of the dial instead.

Any light can charge the watch: sunlight, overcast daylight, ceiling lights or a desk lamp. Citizen says direct sunlight charges it fastest. There is no need to worry about overcharging: the watch stops charging automatically when full.

How quickly does an Eco-Drive charge?

Charging time depends on the movement and the intensity of the light. The figures below come from Citizen’s official manual for the E031 movement. This movement is used, for example, in the women’s watch Citizen EM0500-73L.

Light	For one day’s use	To restore normal operation after the battery runs down	To fully charge
Sunny outdoors (100 000 lx)	2 min	18 min	11 h
Overcast outdoors (10 000 lx)	12 min	3 h	40 h
20 cm from a 30 W fluorescent lamp (3000 lx)	40 min	8 h	130 h
Normal indoor lighting (500 lx)	4 h	60 h	910 h

The table shows that ordinary room lighting charges the watch very slowly. In sunlight, the watch gains a day’s worth of energy in two minutes; under ordinary room lighting, this takes around 4 hours. Other movements have different charging times. You can find your watch’s movement number on the case back: according to Citizen’s guide, it is the first four characters of the case number engraved there. Use that number to find your watch’s manual on Citizen’s website.

How can you tell when the watch needs light?

On many Eco-Drive models with a seconds hand, low charge is indicated by the hand moving in two-second jumps. The exact warning method depends on the model. This is a sign that the watch should be exposed to light immediately.

If you ignore the warning and do not charge the watch for several days, it will stop. For example, Citizen’s manuals for the E031, E111 and E168 movements specify around 4 days from the warning to the watch stopping.

The watch has stopped – what should you do?

1. Put the watch in the light with its dial facing the light source. Direct sunlight is fastest. A bright windowsill also works in winter.
2. Wait until the seconds hand moves once every second again. Two-second jumps mean the charge is still low.
3. Charge it a little longer. Citizen recommends keeping the watch in bright light for the full charging period, not just until it starts running.
4. Reset the time and, if your model has a date display, the date too. After stopping, the time is incorrect and needs to be reset.

Citizen’s manual says to avoid heat when charging:

• do not charge the watch at temperatures of around 60 °C or above, as this may damage the movement;
• do not leave the watch charging on a car dashboard;
• under an incandescent lamp, keep the watch at least 50 cm away.

If the watch stays in darkness for a long time

A watch kept in a drawer or worn under long sleeves receives no light. Citizen offers a few simple recommendations:

• When you take the watch off, put it somewhere as bright as possible. Do not keep it in the dark.
• Long sleeves prevent light from reaching the watch.
• For best results, Citizen recommends exposing the watch to direct sunlight for 5–6 hours a month.

Some models have a power-saving function. When the watch has been in darkness for a while, the hands stop to save energy. The watch continues to keep time internally, and the hands automatically move to the correct position when light returns. Check the manual to see whether your watch has this function.

How to choose an Eco-Drive watch

Our Citizen watches are priced at around €100–900, and almost all are Eco-Drive models. Focus primarily on style, size and features when choosing.

• Classic three-hand watch – simple and suitable for work and everyday wear. For example, the Citizen Eco-Drive BM7460-88H (40 mm).
• Diving watch style – a sportier watch, such as Citizen Eco-Drive BN0100-42E (41 mm).
• Chronograph – a watch with a stopwatch, for those who prefer more detail on the dial. For example, the Citizen Eco-Drive CA7060-88E (42 mm).
• Radio-controlled watch – according to Citizen, an Eco-Drive Radio-Controlled watch receives official time signals and sets the time automatically. The relevant signal can also be received in Europe under suitable conditions; reception depends on the model, location and settings. View Citizen Eco-Drive Radiocontrol AT8154-82L.
• Women’s watches – smaller, at 30–32 mm. For example, the EM0500-73L (32 mm, blue dial) or EM0674-81A (31 mm).

If you are unsure whether to choose solar power, automatic or quartz, read our comparison automatic, quartz or solar-powered.

Citizen Eco-Drive from Käekellad.ee

We are an authorised Citizen retailer. You can find all models on the Citizen brand page. We deliver watches to parcel lockers (SmartPost, Omniva, DPD), with free delivery on orders of €50 or more. All watches come with a 2-year warranty and a 14-day right of return. You can pay with ESTO instalments if you wish. If you have any questions, write to info@kaekellad.ee.