Dual filament bulb
A bulb with dual filament serve the purpose of tail light as well as brake light and its popular by name 1157 bulb. This kind of bulb is very famous in automotive industry which can perform dual action. It mostly consist of two filament – one filament is comparatively thinner to other.
Tail Light
Tail light turns on the moment we switch on the headlight and its the thinnest filament in the tail lamp bulb which glows. As intensity required for tail light is less hence, thinner filament is configured to act as tail light.
Brake Light
Brake light turns on only during braking and its very obvious to have a higher intensity light to serve this purpose. Thicker filament of tail lamp bulb glows during braking which produces more intensity compared to thinner filament of tail light. This is the reason why we see glow of tail lamp double-up on applying brake.
This dual filament bulb serve the purpose of tail light in bike as well as cars. It all depends on the car design from the manufacturer which finalize whether to use dual filament bulb to serve both purpose or deploy separate bulb for tail & brake light.
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