Something You Should Know-Bike Light

Unlike a car where the choice of lights are barely a consideration, a cyclist must carefully choose the right lights depending on the riding conditions, the type of riding, the bike of choice and the duration of the ride.

With this helpful guide, we aim to outline the terminology you need to know, the difference between lights to see with versus ones to be seen, the unique requirements of road riding, mountain biking, and commuting, and also give you an idea of how far your budget will stretch.

Lights to be seen vs light to see

There is one fundamental question you need to ask when shopping for lights – do I need my lights to ‘be seen’ or ‘to see’ with?

Lights that are used to see with generally have a greater brightness, a larger battery to power the brighter light, and a narrow beam angle to see into the distance. Lights that are used to be seen will have a focus on being seen from more angles, with features such as a wide beam and side illumination. The number of lumens is generally lower as the priority isn’t to see far into the distance. As a result, be seen lights are often lighter, with smaller batteries, fewer lumens, wide beam angles and lower cost than lights that are used to see with.

And while you may think you only need lights in the dark, a reported eight out of ten cycling accidents occurring during the day, and the use of lights during the day is the number one thing cyclists can do to make themselves safer according to a Denmark-based study. According to Bontrager’s white paper on the matter, to classify a light as one suited to daytime use, it needs focused optics, an interruptive flash pattern, and a visible distance during the day of at least 400 meters. Bontrager claims – “Using a flashing tail light in the day makes you 2.4x more noticeable than with no lights at all and 1.4x than in steady mode.” Here’s some more information on the use of daytime lights and some of the best ones of 2017

Light Terminology Explained

bike light

Lumen: The number of lumens represents the total amount of light emitted by a given source.

Lux: Lux is the measure of the intensity of light on an area or surface, most commonly this is measured at a distance of between one and ten meters. If you imagine that ‘lumens’ represents the total amount of light emitted by a bike light, lux measures the amount of that light that gets transferred onto a surface a distance away. So assuming that the number of lumens in a light remains constant, the larger the surface area, the less lux. The opposite is also true, a light with the same amount of lumens will have a greater lux value if the surface area is smaller. This aspect is particularly important as we discuss beam angle and bundle later in this article, and which light is best for different cycling disciplines.

Beam angle: The beam angle gives an indication of how much the light spreads from the original source. Some lights have an acute beam angle that focuses directly ahead (increasing a light’s lux), while others have a broader beam angle that spreads (decreasing a light’s lux). This is sometimes referred to as a ‘bundle’. The wider the bundle, the greater the beam angle and disbursement of light; the smaller the bundle the narrower the beam angle and light disbursement.

Beam Type / Setting: Super, High, Full, Standard, Regular, Low, Flash, and Pulse are just some of the various beam types or settings you may encounter. Brands describe the type of beam exiting the light their own way, and so it pays to delve a little deeper into these descriptive terms to find out what each name represents and how that impacts on run time. For example, a light may promote it has a five hour run time (sometimes called burn time), but that may be on ‘flash’ mode which emits a small amount of light intermittently, whereas the same light on ‘full’ or ‘high’ that is emitting light constantly may only last for 30 minutes.

Burn time: How long a light takes to go from full charge to flat on a given beam type or setting.

The differences between lights for road, mountain bike and commuting
Road riding and off-road riding require different approaches to lights. Road riding generally is done in straight lines with few obstacles along the way, so a light that directs its focus straight ahead is ideal. Conversely, off-road riding requires a broader light bundle to illuminate the area directly around you to see tree roots, rocks, and other obstacles.

The main purpose of having a light on the road is visibility, so that should be first on your list. Does it increase your visibility and enable drivers and pedestrians to see you? In order to do this, a light needs to have a broad enough beam to be seen from the side and acute angles, as well as front on.

Road Rules give a clear indication of the minimum lights requirements when riding a bike at night. If you are riding a bicycle at night you must have a white light (flashing or steady) on the front, a red light (flashing or steady) on the back and a red reflector on the back. The lights must be visible from 200m and the reflector visible from 50m. The 200m rule is the key requirement to look for when purchasing lights, regardless of whether they are to see or be seen.

Once you’ve established the light provides sufficient visibility, factors such as price, size, weight, durability and the intended use will all play a role in choosing the right light.

Sam Moore from the cycling accessory company Knog suggests choosing a light with a low weight, specific beam type (broad or narrow depending on your needs), various flash patterns to be seen in the day as well as night, and an adjustable strap. “Don’t always get sucked into the lumens per dollar decision, a light’s optic design – lens, LED’s, beam angles – are as influential on brightness as the lumen number”, says Sam. Suggesting that whichever light you choose needs to fit with the type of riding you do first and foremost. In addition to those essential items, things like good water resistance, USB rechargeability, and quick release mounts are features worth searching for.

Tom Sullivan from BBB says there are three things you should be checking when selecting a light. Do you want to see, or be seen? What light ‘bundle’ do you need? How long will you be riding?

According to Tom of BBB, “the best ‘to be seen’ lights utilize ‘COB’ (Chips on board) LEDs, these allow for a super bright light in a small package. And for a light to see with, ensure the light you select has a quality lens that produces the desired light bundle.” Regarding a specific light bundle, “some lights offer a tight ‘hotspot’ which are great for helmet mounting, while others have a wider bundle which is more suited to mounting on your handlebar.” And regarding ride duration, “ensure the light you choose can maintain a constant output over the duration of your ride” for safety purposes says, Tom.

bike light

In terms of brightness, if you are road riding or commuting and want a light to see with, you should be looking for a higher lumen count and narrow beam angle. This will narrow the focus down the road helping you see well ahead. If you are mountain biking and looking for the best approach to see, a dual light option is best – one handlebar mounted light with high lumens and broad beam angle, and a helmet mounted light with high lumens and narrow beam angle. This combination will throw a good amount of light broadly around your current position, while the helmet mounted light can be used to see far ahead and prepare for corners or obstacles that may be in the distance. It can also be used as a spotlight to focus on specific items in the distance.

If you are commuting during the day or along paths that are well lit and only looking for a light to be seen, opt for a low to moderate amount of lumens with a broad beam angle. This will help drivers and pedestrians see you from acute angles. Tom suggests using a modern reflector to provide “great forward and downlight, with a definitive horizon that helps prevent blinding oncoming traffic.”

Sam has some great advice regarding rear lights in bunch riding, “if you are riding in a peloton or large bunch, you may want a particularly broad beam rear light to avoid blinding your mates.”

Factors to consider when buying a light


bike light

Lumen is the most common descriptor you’ll find on a light, and while it doesn’t tell the whole brightness story, it’s a good place to start. The more lumens, the more light emitted. Sam of Knog has reiterated there’s a lot more that goes into brightness than the amount of lumens but all other things being equal, the greater the lumens, the greater the brightness. Bicycle lights start with as low lumen count as 30 and can go well beyond 2,000.

How bright is too bright? For regular commuters, having a bright light that can be seen night and day, that doesn’t blind oncoming traffic, is essential. As a result, if you opt for a light with a high lumen count, be sure to tilt it downwards slightly so that it’s not directly in the oncoming driver’s eye line. Another idea is to run two sets of lights, one bright light to see with that can be turned off or down when traffic approaches, and another less powerful light that remains on at all times in flashing mode. Having a light in a ‘flashing’ mode makes it easier for drivers to differentiate you from street lights, and has the added benefit of saving power to last longer between charges.


Most bicycle-specific lights will easily mount to the majority of handlebars and seat posts but for those with aero bars or aero seat posts, the mounting of lights becomes far more difficult.

Most lights are either secured in place with velcro, a screw that tightens a bracket around the handlebar bar or seatpost or, are mounted using a stretchable rubber strap. As mentioned, if you have a standard circular bar to attach to this presents no issues, but non-circular surfaces could present a problem as could larger than normal circular diameters, such as double wrapped handlebars. As a result, it’s important to make sure each light and its mount are compatible with your bike.

Many people mount a second rear light to the seatstays for extra visibility, in which case, you need to be confident the mount is secure and won’t turn into your wheel. Look for mounts that easily enable you to adjust the tightness for a secure hold. Also look for lights that come with interchangeable mounting straps for the different post and handlebar diameters. The Knog Blinder Road R70, for example, comes with three interchangeable mounts for 22mm – 27mm, 27mm – 32mm and 32mm+ diameter posts.

Also, consider if you are mounting to aluminum or carbon. A carbon frame can crack if over tightened (which is why you should always use a torque wrench when working on carbon bikes), so a mount with a stretchable rubber strap or velcro is the safer option, as opposed to a screw and bracket method.


Most lights will either be USB rechargeable or require batteries. Most modern lights are USB rechargeable with a Lithium-Ion or similar battery, saving you money by not having to purchase batteries and also being easy and convenient to keep charged. For lights that require batteries, it’s worth making sure they are easily attainable from the supermarket or service station.

Some high powered lights will require a battery pack be carried and plugged into the light in order for it to work (see above image). If you require such a light, be sure you have the capacity to either mount both items to your bike or mount one and carry the other. After you have mounted a light, GPS computer, and bell to your handlebars, there may be little real estate left to mount anything else. Tom suggests this option can be advantageous for mountain bike riders as, “using an external battery helps keep the weight of the light down and off the riders head.”
Simply put, the greater the capacity requirement (in terms of overall brightness and run time) of the battery, the greater the size and weight will be.

Run times

Run time or burn time gives an indication of how long the light will last from being fully charged to flat. The table below shows the variation in run times of lights based on different beam types using the Lezyne Power Drive 1100XL front LED as an example. As you can see there is almost an 18 hour differential between the run time at the brightest setting, compared to the lowest output on pulse. Be sure when comparing the run times of various lights you are comparing the same beam type

Flash TypeBlastEnduroEconomyFlashPulseOverdrive
Duration (h:min)1:452:408:1516:0019:001:15

If you’re one that needs all the light you can get, it’s worth paying attention to how lights handle their run times. BBB refers to a concept called ‘constant output’ when describing their run times. Some other lights will start at a set lumen amount and then gradually decline linearly as the battery loses charge. BBB and a number of other high-quality lights, however, stay at a set lumen for a period of time before activating a ‘get-home-safe’ option, whereby after this set period of time, the amount of light output is lower to save the battery life. For example, some lights will start at 500 lumens and lose 10 lumens per 15 minutes until the battery is flat. BBB’s approach is to have a slightly lower starting lumen number, but keep it constant over a set period of time, for example, a light will start at 500 lumens and stay at 500 lumens for 2hours before the ‘get-home-safe’ option kicks in and it steadily declines.

Bulb types
LED’s are mostly responsible for lighting in modern lights, replacing the halogen bulbs. LED’s are far more efficient than halogen lights, using less energy to produce the same amount of light. High powered HID bulbs made a short appearance in high-end bicycle lights, but much like luxury cars, have since been phased out due to developments in LED technology.


Lights will vary in weight depending on their brightness and battery size, ‘be seen’ lights can weigh as little as 15g, and ‘see with’ lights upwards of 150g. Expect front lights to weigh a little more than the rear ones as they generally have more brightness to light the way.


While exact requirements can vary according to your state of residence, most states have laws that require bike lights between sunset and sunrise or during limited-visibility conditions. In addition to these laws, all new bikes must be equipped with a white reflector on the front of the bike and a red reflector on the rear. These can be removed by the owner without penalty, though you will need to use some form of a lighting device when operating your bike at night.
Though there is no federal code requiring lights, most state laws for bicycle lights are similar to this example taken from the Oregon Vehicle Code (ORS 815.280):
At the times described in the following, a bicycle or its rider must be equipped with lighting equipment that meets the described requirements:

  1. The lightning equipment must be used during limited visibility conditions.
  2. The lighting equipment must show a white light visible from a distance of at least 500 feet to the front of the bicycle.
  3. The lighting equipment must have a red reflector or lighting device or material of such size or characteristic and so mounted as to be visible from all distances up to 600 feet to the rear when directly in front of lawful lower beams of headlights on a motor vehicle.


On almost any decent bike light you purchase, you’ll have a variety of modes to choose from. Which mode is ideal for you depends on the weather conditions, time of day and length of your ride.

Here’s a quick guideline for when to use each setting:


The flash or burst mode can help you to be seen on urban roads when you’ll need to grab the attention of other motorists. These modes can be more dangerous at night because they won’t allow you to see the road and can make it more difficult for other motorists to judge your speed and distance. Keep in mind that the flash and burst mode preserves the life of your battery, so it can be an option when your battery power is limited on lengthy early morning or evening training rides.


This setting drains your battery the quickest (usually in an hour or two), but is also the safest when riding at night. A beam light helps you see the road when street lights are limited and is always a good option when you’re away from the city. If you are riding in an urban area at night, pairing a high beam light with a cheaper flashing light is the way to go for both the front and rear of your bike when possible. This help you see the road and grab the attention of other motorists.


During early morning and evening hours when sunlight might be limited or during medium- to long-training rides when battery life could be an issue, using the constant beam in a lower power setting might be the best option. Using a lower power setting can, in some cases, double your run time while still providing a constant stream of light for other motorists to judge your speed and distance. The medium or low setting also provides some additional light on the road surface — which is helpful for locating potholes and other hazards that may be difficult to pick up with the flash mode.


To see the road and to be seen by other vehicles, you’ll need to purchase a good front and rear bike lights. In general, there are three different types of bike lights:


These lights offer a high number of lumens for maximum illumination on the road so you can see where you’re going. They are higher priced and often have a high-powered beam for riding on roads without street lights.


The primary purpose of safety lights is to help motorists see you. Many options feature very bright LED lights suitable for daytime and nighttime use. Various mounting options and the type of battery used (rechargeable or disposable) affect the price point. Since these lights aren’t meant to help you see where you’re going, they are generally less powerful and cost less than high-output lights.


Often available as a helmet or front handlebar mount, off-road lights are some of the most expensive lights on the market because they are brighter and transmit a wider beam of light than road models to help you see the trail in complete darkness. Because of the power required to operate these lights, run time is often limited.

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