What is a Double-Filament Bulb?
Double-Filament bulbs are simply bulbs that have two filaments. Usually they are manufactured in such a way that one filament gives out brighter light than the other. This type of bulb is commonly used in automobiles and even bicycles.
A basic use of double-filament bulbs is in the car’s head lamps. Instead of using two separate lamps at the front of the car, one lamp may perform two functions. The brighter lamp, which produces the high beam, is basically used to help driver’s navigate the road in darkness or low light. This high beam on one filament serves as the main light from the vehicle. But in not so dark situations, a light that is less bright may be what’s needed by the driver in order to navigate roads safely. The second filament of a double-filament bulb will provide the low beam and this is generally used by drivers when other vehicles are visible on the road, whether ahead of one’s vehicle or part of incoming traffic in the opposite lane. A lower beam is necessary so as not to overwhelm other drivers with too much glare and blind them with the very bright light of the main or high beam. The low beam is also called the meeting or passing beam because it is the beam used when passing or meeting other vehicles on the road.
Double-filament bulbs are also used at the rear end of the car. This particular bulb may be shared by the car’s stop light and tail light. The tail light provides the red light at the rear end of the car and usually this serves as the low beam part of the double-filament bulb. The brighter high beam is intended as the stop light and this will illuminate every time the driver presses his/her foot on the brake pedals. These stop lights are also called brake lights.