Bicycle lights can help make cycling at night safer. In the past, bicycle lights were at times unreliable. They either required batteries, which died quickly and needed to be replaced frequently, or used a generator that ran by actually resting against the tire of the bike, producing significant resistance and varying degrees of light, depending on the speed of the bike. Magnetic bicycle lights, however, use a frictionless technology with sophisticated electronics that provide constant illumination regardless of speed and a much more reliable light source.
Physics
Magnetic bicycle lights use the principles of both magnetism and electrodynamic induction. When a magnet is spun within a coil of conductive wire, the fluctuation of the positive and negative poles of the magnet induces the coil to produce an electrical current that flows through the wire, according to the Reelight website. This, in effect, is an electrical generator. In magnetic bicycle lights, electrodynamic induction is driven by a separate magnet that passes by the magnet within the coil. When the driver magnet passes by, its magnetic field affects the magnetic field of the magnet within the coil, causing it to spin without actually touching it.
Installation
The driver magnets attach to the spokes of one of the wheels, while the induction generator attaches to the fork or frame of the bicycle. The magnets are then aligned so that they pass closely to the generator. Wires then lead from the generator to the lights, which can attach to any number of locations, including the handlebars, steering stem, seat post, fork or frame of the bike.
Function
Once installed, the light will begin to work as soon as you start riding your bike. As the wheel turns, the magnets attached to the spokes will pass by the induction generator. The magnetic field will spin the magnet within the generator. As a magnet spins, its magnetic field will induce the coils within the generator to produce an electric current that will power the lights and charge the battery or capacitor within the bicycle light.
Storage
As the magnetic bicycle light operates, electrical energy may also be stored in either a rechargeable battery or a capacitor. Electronics within the system supplement the power needed to keep the light shining at a constant rate. When the bike comes to a stop and the magnetic bicycle light stops functioning, the system then switches over to 100 percent battery or capacitor power to keep the light on.
Advantages
There are several advantages to using a magnetic bicycle light over other types of lights, according to the Freelights website. The magnetic light does not have any batteries that will eventually die, potentially leaving you in the dark. Magnetic bicycle lights are also relatively drag-free, and will not slow you down, as dynamo-based lights that must make direct contact with the tire of the bicycle are prone to do. Also, unlike dynamo-based lights, which vary in brightness depending upon how fast the wheel turns, magnetic lights provide constant illumination.
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