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Bicycle Lights

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A bicycle and lights

Bicycle lights come in two varieties: dim, flickering things driven by dynamos which make your bike feel like the brakes are on, and battery-powered lights with a life measured in minutes, so heavy that they bend the lamp brackets. Right? Wrong.

In the 1980s, a lamp powered by 'AA' cells would have been a poor thing indeed. Incandescent lamps drained batteries at a staggering rate, so fast that rechargeables provided too short a duration to be useful. Alkaline batteries were available, but expensive. Most lights used heavy 'D' cells which required substantial built-on brackets.

Now, use of overvolted halogen lamps and LEDs (that is, ones run at slightly over the rated voltage, which produce more power at the cost of a shorter life) has revolutionised cycle lighting. The amount of light output per watt consumed is far higher, giving longer battery life and better vision.

Legal Requirements

In the UK, bikes must conform to the pedal cycles (construction and use) regulations and the road vehicle lighting regulations. To be used at night, a bike must have:

  • One steady, fixed white light, marked BS6102/3 (or equivalent), positioned centrally or offside, up to 1500mm from the ground, aligned towards and visible from the front.

  • One steady, fixed red light, marked BS3648 or BS6102/3 (or equivalent), positioned centrally or offside, between 350mm and 1500mm from the ground, at or near the rear, aligned towards and visible from behind.

  • One reflector, coloured red, marked BS6102/2 (or equivalent), positioned centrally or offside, between 350mm and 900mm from the ground, at or near the rear, aligned towards and visible from behind.

  • Four reflectors, coloured amber and marked BS6102/2 (or equivalent), positioned so that one is plainly visible to the front and another to the rear of each pedal.

There are exemptions for older bikes; pre-1990, the light output from the front light to meet the required standard is much lower, and pre-1985, the pedal reflectors are not required. Note that there is no exemption for step-in (or quill) pedals1, which are popular on mountain bikes and almost universal amongst racers and tourists. No pedal reflectors, no night riding - legally, at least.

Flashing-red rear lights are also illegal in the UK, despite being between three and five times more visible. The lighting regulations, which cover both these and the pedal reflectors, are under review, so this may change.

In addition, various regulations pertaining to the sale of bicycles have led to the fitting of white front-reflectors (mainly because cyclists often fail to fit lights) and spoke-mounted wheel-reflectors, which are worthless in almost all situations. They can break spokes and unbalance the wheels. These are not covered by the lighting regulations. Remove them as you see fit.

Other countries have different regulations, but a review of the lights on offer shows that the requirements are fundamentally similar.

You, dear Researcher, are not stupid enough to ride at night without lights. So here is a brief rundown of the options open to you:

Top Tip

Lights have two purposes: seeing, and being seen. The type of light required for each may be different. The solution is obvious: fit two types of lights. You'll never get in trouble for having too many lights on a bike at night (please don't take this as an invitation to fill your Yak BoB with batteries and do a Blackpool illuminations impression just to prove this Entry wrong).

Battery Front Lights

Battery lights are convenient because they are self-contained. No wiring required, just attach them to the bike and off you go. The downside is that you must change or recharge the batteries occasionally at inconvenient moments. Alkaline batteries last longer but when they do fail they go quickly and are unlikely to get you home on their last gasp as old-style batteries would.

The choice in battery lights is tremendous. At the bottom end are the lights sold in pairs (one red, one white) which take 'C' or 'D' cells. These are adequate for being seen, and for an emergency spare, but worthless on an unlit road. They are a good choice for occasional use on town bikes, preferably backed up by flashing front and rear lamps. Do make sure they are marked to the relevant standards. The lamp's output could be 0.75W or less, often less.

Moving on up, as they say, we get the classic Cateye HL-500. Other manufacturers make similar lights, but this has been the benchmark for over ten years. When these lights were introduced, they were revolutionary, being compact, bright, and cheap. With a 1.25W halogen lamp, this is the lowest specification which will actually enable you to see anything meaningful on an ill-lit road. They are always preferable to the lower specification lights above if budget permits. Battery life is moderate, eight hours from a pair of alkaline 'D' cells, and you can get a decent life out of rechargeable batteries.

Step up from this and you get a diverse selection of lamps of varying brightness and battery life. They are all powered by standard format batteries (mostly 'C' and 'D' cells) and are basically variations on the theme with different batteries but fundamentally similar lamps. Micro-halogen lamps are slightly more efficient, giving up to 3h light at around 2.5W from four AA cells. In general, the brighter the lamp the shorter the battery life, so few of these lamps put out more than 3W. If you want a bit more light and are disciplined about charging rechargeable batteries, these are a sound choice.

For a significant increase in light output, you require a significant increase in power availability. Step forward the rechargeable lighting system. Usually powered by a compact lead-acid cell designed to fit in a bottle cage, these systems will run one or two lamps for periods up to five hours, and some even longer. Precise figures are difficult because with a typical system you might have 5W and 10W lamps, allowing three different levels of light which discharge the batteries at three different rates. This is a great choice if your regular journeys go through unlit areas (parks, stretches of country roads etc) as you can really light up the night when the need arises.

Caution is required, though. The batteries are not particularly advanced, and completely discharging them can fatally damage them. Always buy an intelligent charger if this is an option, as boiling the batteries up is also a real risk. Rechargeable lighting systems are popular with off-road riders as they give enough light to see more than just the narrow bit of track ahead. The lights are usually permanently wired to the bike and the batteries are heavy, so if your need is for long battery life rather than quantity of light you might be better off with a dynamo.

Still not bright enough? A new lamp from Cateye, the Stadium 3, uses a 21W metal halide lamp, technology normally only found in projectors, to give the equivalent of 80W of halogen lights. Riding along the towpath of the Styx? This is the light for you!

Battery Rear Lights

At the basic end, we have again the standard 'C' or 'D' cell tungsten lamp. As a rear lamp, it's quite acceptable, if not outstanding. As with front battery lamps, you can buy a range of tungsten and halogen rear lights of steadily increasing brightness, some of which can be powered off rechargeable lighting systems.

Super-bright LEDs appear to be the choice for most riders, both for visibility and for battery life. The best of these will give considerably more light than an incandescent lamp (much less energy is wasted in heat), and fitting a pair to the carrier of your bike should make you visible to even the most nyctalopic (or night-blind) motorist.

Most LED lights will flash (chasers are the most visible of all). If you are hit from behind and you have flashing rear lights, you will be held at least partly to blame - even though flashing lights have been scientifically proven to be more visible. Make sure your chosen LED light is British Standards-approved (or whichever body looks after safety standards in your country) as a rear light, and fit it using the correct brackets. Note: some LED lamps are BS-approved only when used with an optional fixed bracket; the type which clamp around the seat-pin don't meet the standard.

Dynamo Lighting

If you do a lot of night riding, a dynamo is a good choice. No messing around with batteries, no fading out just when you need them. You carry your own power source with you, and can ride through the night with confidence.

Dynamo Front Lights

Dynamo front lamps come in two brightnesses: 2.4W, for use with a standard 0.6W rear lamp and 3W, using the whole output of the dynamo.

Many dynamo lights, front and rear, are now available with a stand-light. This is a built-in capacitor or small battery which powers either the main lamp or an LED for a few minutes after you stop pedalling. This means you are legally allowed to stop while turning right2. A stand light is a sound choice, always go for one if you can.

Always buy halogen, and don't buy cheap lamps3 Philips are rated highly; if in doubt check the CTC site. Tourists are notoriously thrifty and buy the longest-lasting lamps they can. Always carry a spare lamp - it weighs nothing. Pack it securely - an old puncture kit box wrapped in a polythene bag will keep a spare lamp and some "AAA" cells for your rear light safe and dry.

Dynamo Rear Lights

A standard dynamo rear light is 0.6W, markedly less bright than the LED models (incandescent lights waste much of their energy in heat, remember). There are LED-based dynamo rear lights, and one from Busch & Muller which has four LEDs, runs off batteries or a dynamo, has a standlight and a built-in automatic light-sensitive and time-delay switch. Hard to think of anything they've missed! LED based lamps are ultimately brighter per watt consumed, so use an LED one if you can.


There are three main forms of dynamo, all of which typically produce 3W at 6V. Older models are not worth considering, as technology is advancing fast. Most will produce close to full output at speeds of around 5km/h (3mph), and you should look for a built-in zener regulator to prevent overdriving and blowing the lamps at speed.

  • Bottle dynamos bolt to the front fork and run against the tyre (touring tyres often have dynamo tracks) or rim. They can be moved away from the wheel during the day. Historically bottle dynamos have two drawbacks: drag and clag. Recently, though, the drag problem has been solved: the Dynosys LightSpin runs so freely when not under load that it takes several seconds to slow down if spun by hand. It also has a built-in standlight. These features, along with its 4.5W output, have made it hugely popular. Just think: a traditional bottle dynamo would have an electrical efficiency of about 35%. The LightSpin approaches 95%, giving mechanical efficiency in the same region as more expensive hub dynamos. The problem of clag remains, though. The mechanism must be kept clean or it will grind to a halt.

  • Bottom-bracket dynamos fit under the bottom bracket, running against the tread of the wheel, and can also be moved away from the wheel when not required. They are traditionally more efficient than bottles (although probably even the best are hard-pressed to match the LightSpin), and are less susceptible to mud and muck. Some can be operated by a remote lever, saving the need to stop and move the roller onto the tyre. They are also slightly more difficult to steal from a parked bike

  • Hub dynamos are permanently fixed, being built into the hub. Schmitt is probably the best, but Shimano has a range of excellent and very competitively priced models. Rolling resistance is lower with hub dynamos because they use quality roller bearings, and their fully-enclosed design makes them relatively maintenance free. The only downside is that there is some residual rolling resistance even with the lights off. Since this is equivalent to about one foot climbed per mile travelled, it's probably not an issue.

Personal and Flashing Lights

Legally, the only flashing lights allowed on any road vehicle are indicators, at specified positions and separations. No flashing front or rear lamps are allowed.

You, on the other hand, can be lit up like a Christmas tree. Cycle jackets often have loops for attaching flashing rear LED lamps.

So use them!

You can get a set of four flashing red LEDs which mount in the vents on your helmet.

Brilliant! Get some!

Orange flashing LED armbands?


There have been no recorded instances of cyclists being hit by cars because they were too visible. Yes, get a Scotchlite reflective jacket but do attach some flashing LEDs as well.

You might stretch the point and consider luggage also as not part of the bike. This is slightly more dodgy, but not a lot. Triangular reflectors are only allowed on trailers - but if your panniers have red retro-reflective triangles on them, well that's not a fixture or fitting is it?

Not only are flashing lights more visible but motorists, bless their misguided souls, are actually beginning to make the link between flashing lights and bicycles. Which brings us to flashing front lights. A difficult area: hard to do without fixing them to the bike, hence entering the naughty zone. There are yellow and 'white' flashing LEDs. The Knightrider white flashing front LED is like a strobe light, incredibly bright and visible. I wouldn't encourage you to break the law.

Head Torches

These are much favoured by Audax riders (long-distance time trialists). Adapted from cavers' lamps, they attach to the cycle helmet (you wouldn't ride a bike without a helmet, would you?) and obviously you can point them where you like for unparalleled visibility. You can even get acetylene versions! Petzl are probably the best-known.

The best have a separate battery pack - otherwise the battery mounts on the back of the head. You may need an adaptor to run them with rechargeable batteries. The light unit normally has elastic straps, but these will slip around on the helmet and although there are screw holes to mount to cavers' helmets, these are a poor idea for bike helmets. The best solution is probably either Velcro or cable ties. Worth the effort and expense, though, if your route takes you through unlit territory. The real plus is that the light points wherever you are looking, allowing you to see round corners. It may be worth making a home modification to allow the lead to be disconnected if the light unit is permanently fitted to your helmet.

Mounting Lights

Bear in mind the requirements of the regulations, and also the manufacturers' recommendations. Most front lamps are best mounted on the handlebars if possible, and failing that on the brake bosses above the front wheel. Any lower down and you compromise both visibility and projection distance.

Rear lights are best fitted on the back of a carrier if you have one. Mounting on the seat-post is common, but may not meet the standards - and remember, insurance companies will do their utmost to wriggle their way out of paying a claim in case of a collision. A popular alternative when there is no rack is to mount on the seat-stays, the tubes joining the seat post to the rear drop-outs.

Have You Seen The Light?

So, that about wraps it up for bike lights. Be seen and be safe!

1These pedals have no platform. The rider bolts special cleats to the bottom of their shoes, which clip into the pedals. This is safer than toeclips and straps, as the foot can be withdrawn simply by twisting.2otherwise with dynamo lights you may only pull up on the left - for most overseas riders this is of course reversed3Lamp here is used in the correct electrical engineering sense: the little glass bit which most people call a "bulb"

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