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How Turn Signals Work

By: Karim Nice  | 

Turn Signals in Mirrors

From inside the car, the driver sees a dim signal.
From inside the car, the driver sees a dim signal.
Photo courtesy CustomVan.com

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.

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The signal is bright when viewed from an angle outside the car.
The signal is bright when viewed from an angle outside the car.
Photo courtesy CustomVan.com
The signal is bright when viewed from an angle outside the car.
The signal is bright when viewed from an angle outside the car.
Photo courtesy CustomVan.com
The signal is bright when viewed from an angle outside the car.
The signal is bright when viewed from an angle outside the car.
Photo courtesy CustomVan.com

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.

For more information on turn signals and related topics, check out the links below.

Originally Published: May 15, 2001

Turn Signal FAQ

How does a turn signal work?
Turn signals use electricity and circuits to illuminate and flash. When drivers press or lift their turn signal lever, the circuit is activated and electrical power is directed to either the right or left side lights so they can start flashing.
What is a turn signal?
A turn signal is a vehicle light at the front or rear, on the left or right side, that flashes to indicate the car's intended turning direction to other drivers.
Is it a turn signal or indicator?
Both are correct. A turn sign and a turn indicator both perform the same job — and they're the exact same part within your vehicle.
Is it illegal to have a turn signal out?
According to the U.S. Department of Transportation, failure to signal is illegal, and you can get a ticket if you fail to do so, even if your turn signal isn't working.
Who can replace a turn signal bulb?
Anyone can replace a turn signal bulb. It's a relatively simple task that doesn't require a mechanic, just access to your turn signal's old bulb.

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