What bike light you need will depend on what you are using it for. The main difference between bike lights is how bright they are, or what the lumen output is. We have separated the bike lights into three main categories: commuting/urban use, road cycling and off-road cycling.
Lumens are a unit of how bright a light is to the human eye. It is essentially the total amount of visible light emitted from a light source.
Bike lights range from about 5 lumens up to thousands of lumens on higher end lights. Rear lights tend to be between 5-100 lumens, whereas front lights can be anywhere between 10 and thousands of lumens.
Commuting / urban use
Urban areas tend to be quite lit up, so the main aim of your cycle light in this situation is to “be seen”. Safety lights will have constant and flashing light settings, and while you may think multiple flashing lights are over the top, it is the best way to be seen.
If you are travelling down some unlit roads, you will want a slightly brighter light. Anything over 100 lumens will cast a beam onto the road, and will be sufficient for cycling along unlit paths.
If you’re riding, or training, at a fast pace on unlit roads you will need to think about upgrading your cycle lights. The front light is vital for illuminating potential obstacles and hazards when you are cycling at night, and at a fast past it needs to be sturdy too. In this category we recommend getting a powerful, clamp mounted front light, preferably with a lumen output of 200 upwards.
The problem with road cycle lights is that they tend to have a concentrated beam, so you may need to get another safety light so you are more visible from the side.
Cycling off-road at night will be an entirely different experience compared to during the day. The trails will feel unfamiliar, and you will have to be much more alert to stay on your bike.
You will need much more illumination than a commuting light, and it will have to be securely mounted to avoid it falling off when riding over uneven ground.
We recommend a bar mounted light with an output of over 600 lumens, and off-road specific lights will have a wider beam, so that it can light up the path ahead of you.
Batteries and mounts
Most cycle lights now run on rechargeable batteries, but you can still get lights that use disposable batteries. Rechargeable lights usually come with either Lithium Ion (Li-ion) or Lithium Polymer (Li-Po) batteries; these are more powerful, smaller and lighter than disposable batteries, making them perfect for cycle lights.
Rechargeable bike lights usually charge by USB and have an indicator for how much charge they have left, so you don’t get caught out. We would recommend getting a cycle light with a battery life that is slightly longer that your usual ride time, so that you have some reserves if you get delayed.
Cycle lights mount on to the bike in various ways, but broadly they fit into two categories: strap/band mounts, and clamp mounts. Rear lights and safety lights usually use a strap/band attachment, and as they are easy to fit and don’t require tools, they are ideal for commuting bike lights. Heavier, higher powered front lights tend to use a clamp mount as they are more secure, and can handle rough terrain. Both types usually have a quick-release, so you can easily remove the light.
There are also other mounting types for bike lights, one of them being a bar mounted bike light. These are particularly secure and are often used of off-road cycles. You can also get bike lights for your helmet, which are a good way to get another set of lights to improve your visibility on the road (although are not legal by themselves).
The law states that all cyclists must use bike lights between sunset and sunrise, and you must have a red light on back the and a white light on the front. The quality of bike lights has improved greatly in recent years, so there is no excuse to to not have a light on your bike at night.
We have categorised the lights in this post, but there are plenty of lights out there that will suit all of the situations above. Shop around for the most appropriate light for your needs, and stay safe out there!