Many cars also have turn signals in their side mirrors. This is a better spot for the turn signals because if a car is in your blind spot, its driver might not be able to see the back of your car.
These mirrors contain high-intensity light-emitting diodes (LEDs), usually arranged to form an arrow that can point either left or right. The LEDs are positioned behind the mirror glass so that from inside the car, the driver sees only a dimly lit arrow, but outside the car, other drivers see a very bright arrow.
Since the lights in these mirrors are LEDs, the system has an additional benefit: LEDs light up about a fifth of a second quicker than incandescent light bulbs. That may not sound like much, but at 65 miles per hour (105 kph), your car covers 19 feet (5.8 m) in a fifth of a second. LEDs could give someone the extra time and space needed to avoid hitting you.
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