Bicycle lighting
From Wikipedia, the free encyclopedia
Bicycle lighting has two purposes: seeing and being seen. There are many types of bicycle lights available, each with its own advantages and disadvantages. There is no one "best" solution for any rider, and many riders mix and match different technologies to provide the balance that works for them.
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[edit] History
The earliest bicycle and car lights were powered by acetylene (carbide) lamps, now almost unused except by cavers. They were dim and temperamental, and the arrival of battery lamps was welcomed.
Early battery lamps generally used lead-acid batteries, but these were replaced by self-contained cells; lamps became smaller and more reliable. At the same time dynamos were developed which generated energy from the bicycle's own movement. These were more practical, as storage density in batteries was at this time very low.
Not all jurisdictions required use of lights after dark. In the UK the law requiring use of rear lights was resisted by cyclists' groups on the grounds that it downplayed motorists' obligation to be able to stop well within the distance they can see to be clear.
Replaceable-cell battery lights had a renaissance on the invention of alkaline batteries, with much higher storage densities. Moulding techniques for plastics also improved, allowing lens optics to be refined at low cost thus making more efficient use of the light output. During the 1980s the lighting market became more globalised: European riders would have noticed the gradual disappearance of the French "Wonder Lights" and Ever Ready brands in favour of American, Japanese and German products.
In recent times there have been many advances: exceptionally efficient dynamos; cheap high-output sealed-unit halogen lamps originally developed for decorative lighting; improved storage density in rechargeable batteries driven by the computer industry; high-output LEDs; white LEDs; High Intensity Discharge (HID) lights crossing over from the automotive sector.
[edit] Choosing an appropriate lighting system
Batteries, either rechargeable or disposable, are often used to power electric bicycle lights. For bicycle touring, commuting or if managing your batteries is just too much of a nuisance, powering the lights with a electrical generator, or dynamo, may be a better option. Unlike batteries a dynamo lighting system has unlimited duration, but the maximum power output is relatively low (to some extent this is mitigated by good optics and slight overvolting of the lamp; a good dynamo nominally rated at 6 V is generally allowed to produce 7 V or so by its voltage limiting circuitry). In Germany it is illegal, for environmental reasons, to use lamps powered by disposable batteries except on the most lightweight cycles.[citation needed] This has stimulated the market for high quality dynamos such as B&M or Schmidt.
The least expensive bicycle headlights use an tungsten filament lamp. A more expensive, but brighter and more battery efficient alternative is the halogen lamp. The brightest type is the high power High Intensity Discharge (H.I.D) light, which requires special circuitry and a powerful battery. Some self-contained LED headlights are now a viable alternative to more conventional bicycle lights, although many are only suitable for either being seen or emergency use.
Lighting decisions may be driven by the power source (e.g. tourists choosing a dynamo system) or by the amount of light required (e.g. off-road riders choosing a H.I.D. rechargeable), but often it is a matter of personal preference or local availability. A low power headlight and a rear red LED are often sufficient for cycling at low speeds in familiar areas with sufficient ambient lighting. In more challenging conditions, upgrading to a more powerful headlight is recommended. The drawbacks of more powerful lighting may include some combination of greater weight, greater expense, and shorter run time.
A common setup for a bicycle commuter might include:
- a quartz-halogen headlight powered by a rechargeable battery pack or dynamo
- a LED tail light, either steady or flashing/pulsating
- a flashing/pulsating LED front light for conspicuousness
Before purchasing, installing, or using lights in a given area, verify that the lights will meet legal requirements. In some jurisdictions:
- the use of flashing/pulsating lights is prohibited
- lights may have to be certified to certain standards
- the colour of lights may be regulated (e.g. yellow vs. white LEDs for front position indicators)
Whether or not these factors affect the efficacy or utility of lights, your ability to collect compensation in the event of a collision can be reduced if the bicycle lighting did not comply with the letter of the law.
[edit] Legal requirements
Under the International Vienna Convention on Road Traffic (1968) of the United Nations, a bicycle is defined to be a vehicle. Article 44 of the Convention stipulates that: "Cycles without an engine in international traffic shall: (c) Be equipped with a red reflecting device at the rear and with devices such that the cycle can show a white or selective-yellow light to the front and a red light to the rear." In some countries, for example France, it may be an offence to even sell a bicycle not fitted with legally compliant lighting system. However not all countries impose this requirement on their domestic cyclists.
Many jurisdictions require bicycles to be fitted with reflectors at point of sale. In the United States this is regulated by the Consumer Product Safety Commission. CPSC compliant reflectors (also commonly fitted in other markets) have three retro-reflective panels positioned at 30° angles. The standard requires a forward facing white reflector on the front of the bicycle, sideways facing white reflectors on each wheel, a red reflector mounted on the rear, and yellow reflectors mounted on the front and back of each pedal. Some interpret this as an endorsement of reflector-only night cycling.
Many jurisdictions require the use of a headlight and a rear light or reflector after dark. Individual jurisdictions define specific legal requirements in terms of light output and the size of lamp and reflector lenses, compliance with specified standards or they may simply stipulate a minimum distance from which any lighting device should be visible. Some jurisdictions mandate standards which make some safe and practical systems (usually involving LED based flashers) illegal (though those rules are rarely enforced). Most European countries require front and rear lights at night, as do some US states; others allow reflectors only at the rear.
Depending on one's jurisdiction, blinking lights may be forbidden on the grounds that a blinking light is only allowed on an emergency vehicle.
In the UK the law requires a light approved to BS 6102 Part 3: 1986, but allows the use of additional non-standard lights; in practice this means that users of powerful rechargeable systems need to add an additional light to meet legal requirements. Recent changes mean that a flashing LED may be used, but only if it has no steady mode. National cyclists' organisations such as LAB (US) or CTC (UK) are a source of lighting information.
[edit] Safety
The use of lights for night riding is generally recommended as a basic safety precaution, but there appears to be no reputable published evidence that this (or most other conspicuity aids) has a measurable effect on safety. Most authorities hold to the view that lights are an important safety aid for night riding even in a well-lit urban context, and some studies show a correlation between collisions and failure to use lights[1].
It is generally believed that reflectors alone are inadequate for night riding (almost all cycling organisations unconditionally advocate using a headlight at night), but the Consumer Product Safety Commission and other regulatory agencies have declined to mandate the inclusion of active headlamps with new bicycles, citing increased costs compared to benefits and the fact that most bicycles are not ridden at night. [2][3]
It has been estimated that 75% of bicycles used in the United States at night do not meet the legal requirements for lighting[citation needed]. This may be because the majority of unlit cyclists are riding in urban areas with many streetlights.
[edit] Front lighting
[edit] LEDs
Cyclists that ride at night only occasionally opt for an inexpensive LED front light and rear LED flasher. Red or yellow LEDs suitable for use as rear lights have been available for many years. Recently, white LEDs which satisfy the requirements for a front light have come on the market, and some jurisdictions have or are considering making these legally acceptable. Very high-power LEDs are sensitive to overheating and over-driving, if the enclosure and/or driving electronics are poorly designed. Both of these conditions result in significantly shortened lifespan (dimming, or complete burn-out), and the LEDs are expensive to replace. Efficiency of the LEDs in lumens per watt is superior to most halogen lights, but the driving electronics can negate the advantage unless well designed.
Most riders will use alkaline cells to power inexpensive LED lights; these can have a life of anything from under a week to a year or more depending on the amount of riding, and brightness of the LEDs - life will be longer in flashing modes (even though many lights make the LEDs brighter when flashing than when steady to conserve battery life). The brightness of LEDs is rather sensitive to supply voltage, and rechargeable cells, of 1.2 V rather than the alkalines' 1.5 V, often give poor performance.
Low power LEDs are adequate for riding on well-lit streets, but they do not generally project a very bright beam as it is difficult to collimate the output from multiple LEDs into a single usable beam. This can be overcome by using a small number of very high power LEDs - each with their own optics - and it is now possible to get LED equivalents for halogen rechargeable systems (including drop-in replacement bulbs), as well as LED lights for dynamo power. One particular advantage of LEDs in dynamo-powered lighting is that they produce more light at very low speeds (down to 3km/h according to one manufacturer).
High power LED systems often include an option to dim the LEDs. LEDs are very well suited to dimming (running at half brightness will normally give you more than double the battery life), unlike halogen lights, where running a single bulb at half brightness will only give you a slight increase in battery life.
Efficiency is set to increase as white LEDs switch to emitting red, green and blue light to form a white output (current designs use a blue LED, with a fluorescent coating, much like conventional strip lights use). As very high power LED lights become available and major manufacturers start to adopt these high power LEDs to replace their halogen designs (a 3 watt LED offers similar light output to a basic 10 watt halogen bulb - compare this with current generation "very high brightness" LEDs at 0.05 watts), there are grounds to believe that LEDs will replace incandescent lamps whatever the power source. In the future they may even challenge HID lights.
Advantages of LEDs
- Can be cheap
- Long battery life in flashing mode
- Can be very visible
- Efficient
- LEDs last nearly indefinitely (as part of a well-designed light)
- LEDs can be dimmed, usually with a slight gain in efficiency
Disadvantages
- Limited light output, especially in steady mode for many models
- Some models do not run as long on rechargeable cells as on alkalines; environmental concerns
- Illegal in some jurisdictions
- Attractive to thieves. Especially removable types, particularly if not removed when parked.
Low power LED lights are mainly for "being seen", or as an emergency backup, and are the dominant choice for rear lights; higher power LEDs are now moving into the core market for illumination and are subject to rapid technical development at present.
[edit] Home Made LED lights
As with high-power halogen systems, high-power LED systems have attracted self-build enthusiasts, top-end commercial products tend to be similarly high priced - due to the relatively low production volumes for these high-end parts.
[edit] Low-cost battery lights
For occasional use a low-cost battery light can be a sound choice and usually meets legislative requirements. These lights are low power but compensate to this to some extent by using surprisingly good optics. Some newer models are available with LEDs instead of halogen lamps; this is not legal in all jurisdictions.
Advantages of low-cost battery lights
- Low cost
- Easily moved between bikes
- Readily available (both lights and batteries)
Disadvantages
- Cost of batteries (unless rechargeable ones are being used)
- If using rechargeable cells, limited burn time
- Generally low power
In summary, a standard halogen light can be a good choice for the less demanding occasional user. It can also be a useful emergency light if the usual lights are more exotic.
[edit] Rechargeable Flashlights
There are some high-power flashlights, with rechargeable lithium-ion batteries. Although not specifically designed for bicycle use these are a viable alternative to rechargeable halogen lights, though they are still expensive. They can be fastened to the bicycle handlebars with a device called a "Lock Block." Look for a flashlight that has an adjustable spot to flood beam. Although the optics of these flashlights are generally high quality they are still rotationally symmetrical (unlike motor vehicle lights).
Advantages of rechargeable flashlights
- Versatile - can also be used as a flashlight off the bike
- Portable, so theft resistant
Disadvantages
- Limited burn time
- Heavy (rechargeable systems generally separate the weight of the battery from the lamp); weight may be an issue for off-road riders due to vibration
- Optics not optimised for road use
[edit] Rechargeable Halogen Systems
Although these lights were primarily designed for off-road use, where they are almost universal, many commuters and transportational cyclists now choose to use high-power halogen front lights which operate from a NiMH, lead-acid, or Li-ion rechargeable battery pack.
The lights used by most halogen rechargeable systems are cheap, bright but fairly unsophisticated: they project a cone of light (wide and narrow beam options are available) which is good for off-road use but not ideal for road use as it can dazzle oncoming road users. This means that rechargeable halogen lights do not meet legal requirements in some jurisdictions.
Because they use standard commercial prefocused optics, a wide range of power and beam width combinations is available. Most systems allow simultaneous connection of different lamps - for example, a wide and a narrow beam for offroad riding, or a high and a low power beam for road riding.
Advantages of rechargeable halogen systems
- Bright, sometimes very bright
- Readily available
- Can connect multiple lamps to one battery pack; provides flexibility
- Reasonable battery capacity
- Very reliable
- Can usually be easily removed from the bicycle or to prevent theft
- Lamps are cheap, widely available, and come in many combinations of power and beam width
Disadvantages
- Relatively heavy battery
- Limited run-time between battery-recharges
- Hassle of being certain to keep batteries charged
- Batteries have limited life, typically 500-1000 recharge cycles
- Optics not optimised for road use
[edit] Rechargeable H.I.D. Systems
HID lights are the brightest lights currently available for bikes. They are efficient, very bright, but comparatively expensive. They also tend to have high power consumption, so a relatively limited burn time. Other than this they have the same advantages and disadvantages as rechargeable halogen systems, and like halogen systems they are designed primarily for off-road use, having rotationally symmetrical beams which cast as much light up as down.
If using a HID lighting system on the road, lights should be adjusted to avoid dazzling oncoming traffic.
[edit] Dynamo Systems
Dynamo systems are probably the most widely-used worldwide, although they are uncommon in North America. They provide a self-sufficiency which is valued by their users: no batteries to recharge or replace, and permanently fitted to the bike. (Note: bicycle dynamos produce AC, and so are more correctly referred to as alternators or generators, but the word 'dynamo' has stuck in universal usage). There are three main types: hub dynamos are built into the front hub, and are generally the most efficient; bottle dynamos attach to a fork leg and are rotated by a small wheel in contact with the tyre sidewall, they are generally easiest to obtain and cheapest; bottom bracket dynamos bolt between the chainstays behind the bottom bracket and are powered by a roller against the tyre, these are easy to fit and do not wear the tyre sidewall.
Dynamos are generally limited to 0.5A output, nominally 3 W at 6 V, although 12 V dynamos are available and the best nominal 6 V dynamos can produce 6 W at speed, as detailed here. A dynamo behaves as a constant-current device, not constant voltage; this means that the voltage can exceed the capacity of the lamp at speed, causing failure. Historically this was considered a nuisance but these days lamps and dynamos often incorporate zener diodes to prevent it and/or the dynamo can be carefully designed to "saturate" beyond a certain voltage to protect the lamp (saturation is a feature of all permanent magnet generators). Good dynamos can achieve efficiencies of up to 70% (i.e. under 5W of the rider's output is diverted to produce 3W of electricity) and provide full output at surprisingly low speeds, often 4 to 6 mph is sufficient for full brightness.
To compensate for their limited output, dynamo headlights have good optics which focus the limited amount of light in a narrow beam that lights up the road directly in front of the bicycle; this can be seen in Andreas Oehler's side-by side comparison of beam patterns.
To compensate for the fact that dynamos produce no power when stationary the best lights (and some dynamos) have a stand light facility, usually a single blue-white LED powered by a capacitor which will run for around five minutes. It is now common practice to use all the dynamo's output to power the front light; the alternative is a 2.4 W headlight and a 0.6 W tail light. Most good dynamo rear lights now use LEDs instead of incandescent lamps.
Some riders consider the output of dynamo lighting insufficient. Others report that it is adequate to see on dark roads at speeds up to about 20 mph (single 3 W) or more if a 12 V system is used. Whether the output is sufficient or not will be a personal choice.
Hub dynamos are generally considered the best but require a wheel to be rebuilt if retrofitted (your existing rim can usually be reused). Some bikes are available with hub dynamo lighting systems as a factory option; this can be very cost-effective.
Advantages of dynamo lighting
- Unlimited burn time
- Always there
- High-efficiency optics that are designed to maximize the available power for the lamp (optimised for road use)
- Reliable (although see below for issues with bottle dynamos)
- Environmentally friendly and cheap to run
- Unattractive to thieves
Disadvantages
- Bottle dynamos are noisy, can slip when wet, and wear the sidewall of the tire
- Without standlights, when stopping the lights are off
- Limited power output
- Cut out at very low speeds (below walking pace)
- Difficult to remove where theft / vandalism are a problem
- Cheap dynamos produce noticeable drag
- Halogen bulbs run by a dynamo have a relatively short service life (around 100 hours)
[edit] Rear lighting
[edit] Filament lamps
The only real advantage to these is that they are often omnidirectional, being visible through a very wide arc. Newer LED lights have this feature, making lights based on filament lamps obsolete.
[edit] LEDs
In many countries LED flashers are the norm for rear lights. In others such as Germany flashing lights are forbidden by law. In the UK flashing LEDs (front and rear) are legal from October 2005. It has been found that people tend to underestimate the distance to blinking lights and also that drunken drivers are attracted by them, and there is evidence that they are harder to place than a steady light; on the other hand they have also been shown to be between three and five times as visible as a steady light of equivalent brightness. Most LED lights will work in either flashing or steady modes; some have multiple banks of LEDs allowing both at once. The answer is to have one of each, or a light which will do both simultaneously.
The most common power source for rear LEDs is a set of alkaline cells and rechargeable cells . In both cases the battery tends to fail quickly when it goes; it is widely considered good practice to have two rear lights in case a battery fails en route.
Advantages of LED rear lights
- Compared with incandescent lamps, near-infinite service life
- Bright
- Efficient
- Cheap
- Usually a choice of flashing or steady
Disadvantages
- Cheap ones are not very bright and have poor battery life
- Flashing not an unequivocal benefit
[edit] Xenon strobes
An innovation in bicycle lighting, though common in industrial applications, xenon strobes are brighter than LEDs and are used by some as rear lights.
Advantages of xenon strobes
- Very bright
Disadvantages
- Relatively expensive
- High power consumption (short battery life)
- Lamps require fairly frequent replacement
- Intense light can be a serious irritation to other road users
- Brief flash, followed by darkness, can interfere with night vision
- Brief flash, followed by darkness, can make judgement of cyclist's position difficult
[edit] Supplementary lighting and conspicuity
[edit] Headtorches
Headtorches are a useful adjunct to bicycle lights. They can be pointed without steering the bike, giving useful "fill-in" lighting especially on poor or very dark roads. They also allow the wearer to read road and directional signs placed on high signposts.
Some rechargeable systems offer a head torch option powered from the main battery pack.
[edit] Reflective and high-visibility materials
Retro-reflective materials, in the form of reflectors, reflective tape, and reflective clothing, are useful in making a cyclist visible to other road users. Reflective materials can be applied to bike, rider, luggage, and tyres are available with reflective sidewalls.
[edit] On the bike
Reflectors and reflective tape provide additional visibility (especially when applied to moving parts of the bicycle) and are mandatory in many jurisdictions. Pedal reflectors in particular are very visible to following traffic as they move up and down; unfortunately they are not compatible with most clipless pedal systems, although adaptors are available for some.
Reflectives are visible only when in the beam of a headlight, and even then only within a narrow locus. Importantly, they do nothing to light up the road. Reflectors are not a substitute for lights.
[edit] Clothing
On dark roads reflective materials such as 3M's Scotchlite will show up boldly in car headlights. Evidence shows that bright material on the sleeves can prompt drivers to give more passing distance. Retroreflective materials can discourage some oncoming motorists from dipping their headlights, as the rider become less visible if they do.
The colour of lighting should be checked in the rider's area. A single solid colour can disappear under artificial light, particularly yellow sodium vapour lighting, and colour blindness is common; red/green colourblindness can make yellow fluorescent vanish against a green background (hedges or grass). Vests with both yellow and orange fluorescent plus wide strips of reflective may be the best solution.
In recent times electroluminescent clothing has become available to add to the existing array of LED-illuminated armbands and helmet blinkies. An electroluminescent helmet has been patented.
[edit] Measures of light output
There are three units used in the measuring of light output. Manufacturers are in the business of selling product, so do not always quote the most appropriate figure - for example, watts is commonly used, but wattage alone is a poor measure since the light optics will have a significant impact on the proportion of that power which is delivered where you want it.
[edit] Watts
The watt (W) is the unit of electrical) power, the product of voltage and current (watts = volts x amperes). This is only really useful when comparing lights of similar technologies, and even then only in a limited sense. A 3 W halogen dynamo headlight will light the road up about the same as a rechargeable light set of around 7–10 W, but the rechargeable will put out much more light to the sides, which is useful on trails (although wide and narrow beam versions are available, so even this is a generalisation). A 3 W LED is somewhat brighter than a halogen lamp but generally less well focused. HID lights put out large amounts of light and are often quoted in terms like "80W halogen equivalent".
[edit] Candela
The candela (cd) is the SI unit of luminous intensity. Formally, it is the luminous intensity in a given direction of monochromatic light source of frequency 540×1012 Hz having a radiant intensity in that direction of 1/683 watt per steradian. The measured intensity of a given light is thus dependent on many factors, including the colour of the light and the eye's sensitivity to that colour, the optics involved, reflector and lens. This is a more useful measure than watts, despite its complexity, because it defines how much usable light is shed in a given place: a dynamo headlight, which is designed for road use and is focused to place light where it is needed for seeing the road, makes more efficient use of the power of the lamp than lights using rotationally symmetrical optics.
[edit] Lumens
The lumen (lm) is a derived unit for luminous flux, formally the luminous flux emitted into unit solid angle by a non-directional point source having a luminous intensity of 1 candela. Solid angle is expressed in steradians (sr); the solid angle subtended by a surface at a given distance is defined as the surface area divided by the distance squared - imagine a sphere of 1m radius, place a 1cd light source in the middle, and the luminous flux expresses how much light (1 lumen) will fall on each square metre of the inner surface of the sphere; i.e. 1 cd = 1 lm/sr. Lumens per watt is a common measure of the efficiency of a light source. Clearly the luminous flux of a light source is of little value in isolation; the light will be changed by the optics. Luminous intensity is a much more useful measure, although lumens per watt is a handy way of comparing the output of otherwise similar lights.
