A guide to Bike Lights (Part 1)

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Jan 24 2017

A guide to Bike Lights (Part 1)

The history of bike lights

There was a time when bike lights were simple things. You really had three choices:

  1. A dynamo driven system that gave variable light depending on how fast you peddled and also helpfully wore out the sidewall of your tyre at the same time
  2. A battery powered lamp that was so big it could double up as a coastal shipping warning system when you weren’t using it on your bike; or
  3. Nothing at all and wing it.


Vintage Bike Lights

How it used to be – when your lamps weighed almost as much as the bike!


Nowadays, the world is more complex (plus there are legal requirements to be aware of). We have LEDs, USB rechargeable lights, interruptive technology and more besides. To make sense of what you need to know, Criterium Cycles has put together this guide to bike lights (Part 1). In Part 1 we look at general information on lights as well as lights for road and urban cyclists. In Part 2, we will look at Mountain Bike lights and other more specialist gear such as helmet mounted lights.


The Law

It’s best to start with what the Law says because that’s the minimum requirement. All bikes and bike lights must comply with something called Road Vehicle Lighting Regulations (1989 – with many subsequent amendments) or RVLR for short. In plain English, RVLR says that you must have your lights switched on from sunset to sunrise.  This is not the same as the hours of darkness. If the sun has set, you need your lights on – period. It’s worth getting it right – failure to show the correct lights or reflectors can result in a Fixed Penalty Notice or even a fine which, if issued by a Court, could be up to £1,000. More specifically:


Front Lights

You must have at least one white front light positioned either centrally or offside and it can be up to a maximum of 1500mm from the ground. If capable of emitting a steady light (see the section below on Steady and Flashing lights) it must conform to BS6102/3 or an equivalent EU standard.


Rear Lights

You must have at least one red rear light, again positioned centrally or offside. It must be mounted at a maximum of 1500mm from the ground as well as a minimum height of 350mm from the ground. If capable of emitting a steady light (see the section below on Steady and Flashing lights) it must conform to BS6348 or BS6102/3 or an equivalent EU standard.


Pedals & Reflectors

In order to comply fully with RVLR, you will also need a rear reflector and four pedal reflectors.


Flashing Lights

In 2005, the RVLR were amended to permit flashing lights on a bike as long as they flash between 60 and 240 times per minute.


Challenges with RVLR

In reality, not all bike lights available to purchase today have the requisite BS accreditation. The British Standards for bike lights are over 30 years old and were designed for lights with filament bulbs rather than LEDs. In practice, many LEDs do comply with British Standards which means that some don’t.


Lumens, Lux & Optics


A Lumen is a unit of measuring light that measures the total amount of light emitted from a light source. It’s a generalisation but a fairly accurate one, to say that the higher the Lumens, the brighter the light.



However, Lumens are only part of the picture, because it is a rather one dimensional measurement. Lux on the other hand is a particularly useful value because it measures the amount of light output for a given area. One Lux = one Lumen per square metre. Lux therefore allows us to measure the intensity of the illumination from a light source.


Lux v Lumen

Lux v Lumen – Photo: Xrayvision.net

Optics / Beam Shape

We can see from Lux that if the light source has a high Lumen value but is focused on a small area, we will see that as a very bright light but perhaps not all that useful because peripheral light may be poor. Peripheral Light may be important to you if wish to illuminate objects not directly in front of you such as pavements or lampposts! If the light source is spread over a wider area, peripheral illumination may be better but the overall light may appear weaker. Some manufacturers have spent a great deal of time, effort and money developing increasingly sophisticated optical systems. These aim to give you the best of both worlds and the benefits can be dramatic.



When buying lights, don’t just be impressed by massive Lumen values. Look at what the manufacturer is promising in terms of light intensity and optics because they are very important. If you’re still concerned, check out our handy guide below that explains the different kinds of lights on the market and how they best suit different applications.


LEDs or not

These days, LEDs are so prevalent that the practical choice of having LED or not doesn’t really exist. They have significant benefits too. They are cheap, reliable, are cool wen switched on (in temperature terms!) and are pretty bomb proof when used on a bike that’s going to receive plenty of vibration input.

LED Lights - small, cheap and powerful

LED Lights – small, cheap and powerful

However, just because something says it’s an LED doesn’t mean it’s top quality. Bulbs labelled LED come in variable power and quality. Always focus on Lumens, Lux and Optics, make sure you purchase a light that is suitable for your preferred application. Always purchase from a reputable manufacturer. Criterium Cycles only sells lights that we consider to be from reputable brands.


Steady or flashing lights

Daytime lights

In 2005, the RVLR were changed to permit flashing lights. Some cyclists don’t like them because they find the intermittent nature of the beam irritating. Furthermore, some motorists don’t like them for pretty much the same reason.


Bontrager recently carried out some fascinating research. They discovered that 80% of all cycling accidents occur during the day. They therefore began to focus on designing daytime cycling lights that can be left on at all times, not just during the required hours of between sunset and sunrise. Bontrager cited evidence from the motor industry which they say demonstrates that when cars adopted daytime running lights in the US, an accident reduction of 25% was observed.


Bontrager do say though that even having a light switched on during the day is not optimal solution. For a start, they observed through their own research that the single best way for a cyclist to increase the chance they will be seen by a motorist is to use a flashing light that’s daytime visible. To be daytime visible means using optics that direct and amplify the beam to both intensify it and extend its range.


Flashing Lights – Constant Pulse or Interruptive

Bontrager’s research showed that using a steady mode daytime light (i.e. switched on all the time) makes you 1.4 times more noticeable than with no light at all. A pulsing light is good but the challenge is that the repetitive nature of the pulse can become ‘predictable’ and familiar in the eyes of other road users. Bontrager developed an interruptive flash pattern that they say significantly improves the chance of you being noticed. In fact, Bontrager claim interruptive flash patterns are so good, they increase the chance of you being noticed by 2.4x compared to having no light (a steady light was just 1.4x compared to having no light).


Check out the video below to see what John Burke, President of Trek, says about daytime lights and interruptive lighting technology.



Batteries and Rechargeables

Considering all the other rapid advances in lighting technology that have taken place, the world of batteries is still surprisingly pedestrian. The lead-acid battery was invented around 1859 and is still the most prevalent battery technology used to start the internal combustion engines of motor cars. The most common primary battery in use today (primary being a cell that it is used till exhausted then discarded) is the zinc carbon battery. These are the alkali batteries we buy in their millions today.


Secondary, or rechargeable batteries have obvious advantages. They may be more expensive to buy at the outset but their whole life cost should be cheaper. One of the earliest rechargeable batteries was the Nickel Cadmium battery. This has been largely superseded by nickel-metal hydrogen batteries. All these batteries are sensitive to overcharging and overheating so as a result, their charging has to be regulated and can take some time.


The big leap forward came with lithium-ion batteries. Since lithium is one of the lightest of all elements but has high electromechanical potential, the lithium-ion battery offers a good combination of high voltage and compact volume. Currently, the best batteries in the best lights that are rechargeable, usually using something as simple as a USB port, are Lithium-Ion


The next leap forward may well come with lithium-air or nano technology batteries. Lithium-air in particular could be great for cyclists. These use oxygen as an oxidiser rather than a material. This could mean batteries that are a fifth the price, are five times lighter and last five times longer than lithium-ion. We can’t wait, but it seems we may have to for a while yet.


Quality is everything so only buy from reputable manufactures. We really do recommend rechargeable batteries – the battery technology is better and you will save money over the medium term. Plus you produce a lot less waste!


Which lights to buy?

It can be a bit confusing so here’s a run down of the various lights you can buy for road and commuting use. We’ll cover Mountain bike lights and Helmet lights in Part 2 of this blog.



Mini Lights

Emergency and Micro Lights

These tend to be lights for ‘being seen’ rather than ‘seeing’. We would not recommend them for regular use but if your main light fails, they are a good emergency back up and better than no light at all. Silicone straps such as those found on the Blackburn Click Voyager and Click Mars lights below mean they are easy to attach. They come with CR2032 coin cells.

Blackburn Click Voyager and Mars combo

Blackburn Click Voyager and Mars combo


Mini Torches

Like the Emergency and Micro Lights, we still say these are lights to be seen rather than lights for seeing but the more powerful ones do start to be more practical for general use. Almost all the lights you can get in this group are USB rechargeable so you do need to make sure you keep them topped up even if you aren’t going to be using them all that often.

Cateye Volt 200

Cateye Volt 200 Front Torch


The good news in this category is you are spoilt for choice. These are lights where you can now be confident you are going to be able to see the road ahead rather than just be seen by other road users. Either USB chargeable or with a separate battery pack, Torches almost always have multiple modes. These offer different levels of lumen and frequently have a strobe mode as well for the pulse lights. On full power mode, the biggest torches are in the 1000 lumen category but on the lower power settings, they can last for hours.

Cateye Volt 500 XC front torch

Cateye Volt 500 XC front torch


We are a huge fan on Bontrager’s Ion 700/800 front light and Flare Rear light. With 4 modes on the front and a rear light that can be seen for up to 2km, both these lights come with interruptive technology as standard. This set is a top staff pick for Criterium Cycles – most of us have a set of these!


Bontrager Ion 800R and FlareR

Bontrager Ion 800R front and FlareR rear light set

Battery Packs

Often associated with the higher power systems, the big advantage of the battery pack lights is that you can swap over the battery packs, very handy if you are out on a really long ride or absolutely definitely don’t want to risk getting caught out in a really dark location such as when off road. We’ll look at battery pack lights in more detail in Part 2 when we consider Mountain Bike lights.



Specialist applications

Increasingly we are seeing more and more developments for specific applications but which may themselves become mainstream in the near future. Here’s just a couple of the ones we really like.


Integrated Systems

If you like the idea of indicators but want to keep a more traditional lighting set up then an integrated remote system such as Bontrager’s Transmitr system could be just the thing. Compatible lights can be connected to a handlebar mounted control panel to give you total flexibility over your lights as well as indicator style functionality. Check out the video below to see what we mean.



One of the problems with standard rear lights is that they emit a constant light source (whether static or flashing) whatever speed you are doing. If you are driving a car and the car in front brakes hard, the rear lights change in intensity to let you know what’s happening. Now you can have similar tech on your bike. This Cateye Kinetic has a built in Accelerometer that intensifies the light when you brake and slow down. Be careful though – this light is not a brake light. When you stop, the light will revert to its normal intensity unlike a car when you keep your foot on the brake pedal, even when stationary. Still, the kinetic does change during the process of braking which does have value.


Cateye Rapid X2 Kinetic rear light

Cateye Rapid X2 Kinetic rear light

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