In the city there’s enough ambient light that you just need small, fairly bright units that other road users can see. They can be combined with reflectors to increase your profile.

For unlit roads you need something more powerful. Efficient, bright LEDs and lithium-ion rechargeable batteries mean compact lights can now pack an incredible amount of power. They’re great for long-distance commuting.

Light source

Most bike lights use Light Emitting Diodes (LEDs), which emit light by being switched on and off quite quickly. If you switch them on and off for different lengths of time you can boost or reduce output.

Switch and modes

The switch should be easy to use but hard to turn on accidentally, to prevent flat batteries. It also needs to be well sealed, and offer at least one flashing mode and one­ constant.

Mounting

Needs to be strong enough to hold the light over bumps but also offer a quick-release style system for removal. Mounts that require no tools to fit are a bonus but by no means ­necessary.

Beam patterns

Some lights feature a beam similar to that of a car or motorbike. This means the top of the pattern is essentially cut off, allowing a bright light to be used without it dazzling road users.