Lights and reflectors for bikes

This article was published in 2010, in Newsletter 92.

Why bother with lights and reflectors?


There are many different reasons for having bike lights and these influence what sorts of lights one needs.

To be legal. The law says bikes must have lights. In order to be legal the lights must be correctly positioned – see our Cycle Lighting Poster (enclosed with print copies of this newsletter and available on our website at – and must generally meet BS 6102/3 or an equivalent European standard. ‘Equivalent European Standard’ is a rather vague phrase, but it is generally agreed to mean a standard at least as good as ours but from another EU country. The only one I know which unambiguously and uncontroversially conforms to this is the German StVZO standard.

The legislation covering bicycle lighting is the Road Vehicle Lighting Regulations 1989 (amended in 1994 and 2005), normally abbreviated to RVLR.

Flashing lights are only legal as the primary light if they flash between 60 and 240 times a minute with even flashes, emit at least 4 candela, and … have BS or equivalent approval

However, as the police hardly have the resources to stop people cycling without any lights at all, you are very unlikely to be stopped by anyone checking whether your lights meet the standards. If you were in an accident it might just be an issue.

To be seen. The light we need for this will scatter the output over a wide angle, although it may ‘weight’ it towards the central direction (straight ahead or behind). It may be flashing or steady. Light-coloured or high-visibility clothing also help, as do extra lights, reflectors and reflective material.

Our Cycle Lighting Poster, included with this newsletter. If you don’t have a paper copy or want more, please contact us
Image as described adjacent

To see. Seeing where you are going and whether there are any obstacles is important, especially across commons and on rural routes where there are no street lights. This will need to be a steady light, and with a beam shaped appropriately to illuminate the road without dazzling other road or path users.

To set a good example – it doesn’t do cycling good for cyclists to be branded as law-breakers who cannot even bother to have working lights.

To cover yourself in the event of an accident – you don’t want to run the risk of being made to carry any or all of the blame for any accident, as this can reduce any compensation that you may otherwise be due, either for injuries, or for damage to bike, clothing, or luggage. It could potentially even mean you having to pay compensation to the other party in any collision.


Legally, you MUST have a red reflector to the rear of the cycle and amber reflectors fitted to the front and back of both pedals (unless your bicycle was manufactured before 1985 when do not need pedal reflectors). At point of sale, a bicycle should also have a white front reflector and white or yellow wheel reflectors.

All legally-required reflectors must conform to BS 6102/2 or an equivalent European standard.

You may fit additional reflectors, but must not show a red reflector to the front or a white reflector to the rear.

The rear reflector may be incorporated in the same physical unit as the rear light.

Choosing lights

There is a huge range of bike lights available, from tiny ones that fit in a wallet to very powerful but bigger and heavier ones. Not all are suitable for all purposes: the very small ones may not meet British or European Standards, while at the other extreme, heavy and powerful lights may still not meet the standard because they may dazzle other road users!

Within reason though, anything is better than nothing. Of course, none of them is any use if left at home!

This brings us to the first question – dynamos or battery powered lights?

Dynamo lights

Dynamo lights have the benefit of always being on the bike, and once purchased they are cheap or free to operate (halogen lights need spare bulbs occasionally, and you should always carry one and know how to fit it). Hub dynamos are more efficient and reliable, but far more expensive than roller dynamos, which press against the tyre.

Some tyres are not suitable for driving sidewall positioned roller dynamos, and there is a more rarely seen type which fits behind the bottom bracket (in front of the rear tyre) and is driven by the centre of the tyre tread, although these are of course unsuitable for use with knobbly mountain bike tyres.

A light for a hub dynamo will need a switch, if you want to be able to turn it off, although there is so little drag from a good hub dynamo that you may choose to leave an LED running. Halogen bulbs are better conserved by being switched off when not needed.

The best dynamo lights incorporate a standlight (a small capacitor or battery that stores enough power to keep the lights working for a couple of minutes when you stop).

Battery lights

Battery lights are usually only fitted when required, and may be at risk of theft if left on the bike; they can however be transferred more easily between bikes, so may be more economical if you have more than one bicycle. They also allow you to choose the appropriate light for the trip you are making – why take an expensive high-quality light for a few hundred yards in a brightly lit area, or carry super bright off-road lights (which may well be illegally bright on the road and will certainly have heavy batteries) when you have no intention of straying off the tarmac. In a brightly lit town a cheap blinking LED may actually be better, and is easier to slip into a pocket when you lock the bike up.

The cheapest lights are small battery lights with a LED.

The most expensive are large battery lights with an HID (high intensity discharge), halogen bulb(s) or multiple LEDs with huge power output and dedicated rechargeable batteries. It is actually possible to spend over £1000 on a bicycle light!

Types of battery

Unless you have unusual needs, it is generally better to stick to lights which use standard types of battery (AA, AAA) as you can obtain these almost anywhere if you get caught out. Even if you prefer to use rechargables (and I do), both the cells and the chargers are readily available.

Disposable batteries may be best if you only have a very occasional need for lights or a requirement for extremely long endurance, as they have a long shelf-life and good capacity (if you buy alkaline or lithium cells). Lithium cells have the largest capacity of anything for their weight and size, but are expensive.

If you have a need for very powerful lights (maybe for off-road use) you will probably be stuck with dedicated Li-Ion or Lead Acid cells, which are much more expensive and need a dedicated charger. Prices are high for this type of light, and they probably fall outside the scope of this article.

Alternatives: solar-powered and wind-up lights exist, but they are probably best regarded as novelties or experimental at present.

The lighting unit

Light sources can be incandescent bulbs, LEDs or HID.

Incandescent bulbs (mostly halogen) are the conventional sort, and it is only relatively recently that has been any alternative to them. The lights are usually in the middle range of output unless powered by a dedicated battery system, and they are not as efficient as newer LED systems. They are, however, still popular, and some of the best low priced-but-legal headlights use them. If they are battery powered they will either be heavy or have a very limited range. I only know of a few currently available incandescent rear lights, and they are all designed for dynamo use, so would need a battery case adding if you wanted to use them that way.

LEDs form by far the largest segment of the cycle lighting market today, and with good reason. They are efficient, can have a high output for the power they consume, have extremely long life (typically 100,000 hours) are almost completely immune to ‘blowing’, and can be switched on and off as fast or as often as you like, making them the only sensible choice for flashing lights. Almost all currently available battery rear cycle lights are LEDs.

HIDs are very bright, very expensive, use lots of power, and are unsuited to frequent switching on/off (so are no use as a flashing light). They fall firmly into the type of light that is beyond the scope of this article.

Flashing or steady?

For conspicuity, flashing lights do have some advantages, as they have a tendency to draw the eye, and as no other vehicle uses flashing head and tail lights they do highlight the presence of a bicycle. Steady lights are less immediately conspicuous, but are easier to follow, so drivers can work out where you are going more easily. Flashing lights are only legal as the primary light if they flash between 60 and 240 times a minute with even flashes, emit at least 4 candela, and (if they are capable of a steady mode of operation) have BS or equivalent approval. They are useless for seeing where you are going outside street lit areas. It is very uncomfortable following someone with flashing rear lights, so it is good practice to switch them to a constant mode when riding as part of a group.

Beam pattern: we don’t want to waste light where it is not needed
Image as described adjacent

A steady, bright headlight is essential for riding outside street-lit areas.

Beam pattern

Lights used entirely in street-lit areas only need to be visible to others, but outside those areas they need to let you see properly. This is the point at which a front position light (all that is legally required) becomes a real headlight. Headlights require us to consider the beam pattern – we don’t want to waste light where it is not needed, or to direct it into the eyes of other road users. We do want to illuminate the road in front of us to a reasonable distance, and far enough to the sides to make it possible to see where we are going on bends and corners. This is a very good reason (apart from the legal one) to use lights which conform to a decent standard (UK or otherwise) for this type of lighting. The best alternative to the British Standard, from our point of view in the UK, is the German standard. This is because 1) it is legally acceptable here, 2) lights that conform to it are surprisingly even more readily available than BS approved ones, and 3) they put the light where we need it.

The German standard is called StVZO, and the approval number will be embossed on the light casing as a ‘k’ followed by 3 numeric digits.

The best-known brand for both battery and dynamo lights that are all legal in the UK is Busch & Müller, and they are very good indeed, although they have no blinking lights, as these are not legal under German regulations. Many other brands are available, but I know of no other which only supplies lights that meet relevant standards. Many lights are only suitable as ‘supplementary’ lights, as they have no approval at all, and this includes almost all the Chinese lights available on well known internet auction sites. They’ll light up the road (and the retinas of oncoming drivers), and the police probably won’t bother you, but as the power of cycle lights keeps rising, I expect the powers that be to start expressing an interest in lights which dazzle oncoming road users.

Using lights

Position them carefully – see the Lighting Poster for legal requirements – especially if you want them to light your way. It should be directed so that the beam does not dazzle oncoming road users.

You can choose to adjust a proper bicycle headlight as a ‘dipped beam’, and fit one of the super-bright torch based lights as a ‘high beam’, but if you do, make sure you can switch the high beam off as soon as you see any oncoming road user.

Better quality lights will often have alternative or additional mounting brackets available, and if you use the same lights on more than one bike it is well worth getting additional brackets, as moving them between bikes takes time, is fiddly, and risks damaging them. You may also wish to mount a light in a different position, so that it is not obscured by luggage.

You may find it advantageous to use two rear lights, so that one can be flashing and one steady, as well as providing back-up for each other.

If you ever have reason to take a bicycle on a railway platform, make absolutely sure that all lights, particularly RED lights, are OFF. If your rear light is a standlight with no off switch, cover it securely. It is a serious breach of railway by-laws to display a spurious red light on or alongside the track, and can cause major disruption to services.

Battery care

Unless you use disposable batteries, you will need to consider how to get the best out of them. The most common type is the Nickel-Metal Hydride cell (NiMH), Their major problem is that they self-discharge when not in use, so the cells that you charged up and put in the lights may be half-flat a few weeks later when you need them. The latest type, Low Self-Discharge (LSD) NiMH cells do not suffer from this. They are also usually supplied pre-charged, which explains the other name they are given – Hybrid cells (pre-charged like a disposable, but rechargeable).

Cheap chargers just push power into the cell, and may keep doing so even if it is already full, or switch themselves off with a timer before a full charge is reached. This is bad for the cell, and should be avoided. Better chargers will measure the rate of change of the battery voltage, the temperature, and the time on charge, and use all three in deciding when to reduce to a trickle ‘maintenance’ charge. A good charger may also recondition the cells, and will indicate any that are faulty. Rechargeable cells work best if you use all their capacity every time, so unless you really need to avoid replacing cells mid-ride, it’s best to carry the fresh ones as spares and only fit them when the lights go dim. Then just recharge the ones that are fully discharged when you get home.

Always carry spares!

Bulbs need to be regarded as consumable items, and you should make sure you know how to change them and always carry a spare.

Handlebar ends or under the saddle are good places to keep a spare bulb, rolled in bubblewrap, if there is no space in the light housing itself.

Phil Lee