Watts

The watt (W) is the unit of power, and is usually quoted for the electrical power input, not the light power output. Electrical power is the product of voltage and current (watts = volts × amperes). Input power is only useful when comparing lights of similar technologies. A 3 W halogen dynamo headlight will light the road up about the same as a rechargeable light of around 7–10 W, but the rechargeable usually outputs much more light to the sides, which is useful on trails (although wide and narrow beam versions are available). 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 “80 W halogen equivalent”.

Candelas

The candela (cd) is the SI unit of luminous intensity, that is power per unit solid angle, weighted according to the sensitivity of the human eye to various colours of light. A typical candle produces light with about 1 candela of luminous intensity. A lamp can produce higher luminous intensity either by producing more light, or by focusing it tighter. The luminous intensity of a light depends on many factors, including the colour of the light and the eye’s sensitivity to that colour, the optics involved, reflector and lens. Despite its complexity, it is a more useful measure than watts, because it defines how much usable light is shed in a given place: a dynamo headlight designed for road use and focused for seeing the road makes more efficient use of the power of the lamp than lights using rotationally symmetrical optics.

Lumens

The lumen (lm) is the SI unit for luminous flux, the total amount of light emitted by a source, weighted according to the sensitivity of the human eye to various colours of light. Lumens per watt is a common measure of the efficiency of a light source. The luminous flux is of less value for bicycle lighting due to the importance of directionality. Luminous intensity is much more useful, but lumens per watt is a handy way to compare the output of otherwise similar lights.

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] Automatic turn signals worn on hand

In recent times, automatic turn indicators became available. They react to a change of orientation (an angle) in relation to Earth gravity; they blink only when a cyclist’s hand is out-stretched to indicate a turn^[11].

[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, mainly older SPD models, and a few single-sided designs are available with built-in reflectors. In the UK, where front and rear pedal reflectors are compulsory after dark, most cyclists with clipless pedals are therefore riding illegally. The law is rarely, if ever, enforced, but could potentially be used in court to reduce financial compensation if the cyclist was hit by another vehicle. The CTC have suggested that the requirement could be waived if the cyclist fits an additional rear reflector and/or lighting, but this was not changed in the last revision of the UK vehicle lighting laws (which permitted flashing LEDs). Riders of recumbent bicycles have pointed out that the pedal reflector requirement is nonsensical for them, since the reflectors point straight up and down in use, and are invisible from other vehicles. As of 2008, California law allows white or yellow shoe reflectors (front and back), or reflective ankle bands, in lieu of pedal reflectors.

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.

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), although people with red/green colourblindness dispute this. 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.

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 (32.19 km/h), (single 3 W) or more if a 12 V system is used. LED headlights typically give 2-3 times the light output of a halogen lamp for the same power, due to their greater efficiency.

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 produce light when the bike is stationary, some dynamo lights have a stand light facility, usually a single blue-white LED powered by a capacitor, which runs for around five minutes. It is now common 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. Increasingly, dynamo headlights use LED light sources for the main beam as well as the standlight; some manufacturers include B&M, Supernova (both German) and Solidlights (British). In these newer lamps, the dynamo output requires substantial cleaning up and rectification by electronics before it can be used to drive an LED, whereas a conventional filament lamp will run happily on the “raw” AC from the dynamo.

For higher-powered lights, an external battery pack is often required. These battery packs usually strap to one of the horizontal bars on the bike, or come in the shape of a water bottle to mount in the bike’s water bottle holder. A cable connects the battery pack to the light.