Lights after dark, no exceptions

From dusk until dawn, and at any time visibility is poor, your bike must show a white light at the front and a red light at the back. This is not advice. It is the single most enforced rule affecting cyclists in Copenhagen, the police run targeted checks on it through the winter, and being a tourist on a rented bike is not a defence anyone accepts.

Reflectors are required as well, and they are a separate requirement from lights rather than an alternative to them. A bike needs a white reflector facing forward, a red one facing back, yellow reflectors on both pedals, and reflectors on the wheels or reflective sidewalls on the tyres. Reflectors only work when something shines on them, which is why they can never replace a light.

The lights must actually make you visible. A single small blinking light clipped to a bag is not enough on its own - what is required is a light that shows your position clearly to someone approaching. Steady lights are the safer choice in traffic anyway, because a blinking light makes it much harder for a driver to judge how far away you are and how fast you are closing.

If you are on a rental, check the lights before you ride away. Once you are moving, the condition of the bike is your responsibility and not the shop's - the fine goes to the person riding. And remember how far north this city is: in December it is dark by the middle of the afternoon, which catches out a great many visitors who set off in daylight.