Cycles of all sorts

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. Energizer once made a 2.4W halogen rear lamp, which was essentially a headlamp with a red lens, but most rear lights only need to be around 0.5W.

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

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