Headlights

BEHAVIOR

They light up your life—or at least the highway in front of you. Neither

rain nor snow nor dark of night can stop them from illuminating the way. However, a dense fog can really cut into their effectiveness.

HABITAT

Draw a picture of an animated car driving toward you and the headlights

are where you would put the eyes of the car. One is mounted on each side of the front of the car, outboard of and below the hood.

HOW IT WORKS

Most cars have halogen lights. Like traditional incandescent light bulbs found at home, halogen bulbs have tungsten filaments. The bulb itself is much smaller than an incandescent bulb and is made of quartz, not

glass, and is filled with halogen gas. The halogen interacts with the tungsten to redeposit tungsten back onto the filament so it lasts longer than tungsten filaments in bulbs at home. As hot as a bulb at home gets, the halogen bulb gets much hotter—too hot to use glass, thus requiring the quartz bulb.

The silver-colored material in the headlight reflects light outward so more of the generated light is useful. Dual-beam headlights have two filaments in each headlight. Pulling and holding the high-beam lever can turn on both filaments at once. 

On cars sold in the United States, low beams consume 45 watts of electric power and high beams consume 65 watts.

Some cars come equipped with High Intensity Discharge (HID) headlights that cast a blue tint. They operate like the mercury vapor lamps used in some street lighting, except that they don’t have the slow start up that mercury vapor has. The gas inside (xenon) is exposed to a very high voltage electric arc that excites the gas atoms into a higher energy state. When they return to their normal state they emit photons of light. As the bulb heats up, the gas inside becomes a plasma—ionized gas. HID lights give off more light per unit of electric energy consumed than traditional headlights do.

Most cars today have sealed beam headlights. These are enclosed to prevent air from moving in or out. Each unit has a filament, reflector, and lens.

Headlights on luxury cars have cleaning or wiping systems. Mercedes has a squirter that emerges from behind a panel when you press the button to clean the lights. Other cars have mini-wipers to swish away the dirt and snow.

INTERESTING FACTS

Early automobiles relied on carbide or acetylene gas lamps. Calcium carbide mixed with water generates acetylene (C2H2) which burns when ignited. It also explodes and is used in carbide cannons.

Headlights in most cars are designed for use only on one side of the road. The lights are pointed downward to the outside of the road so they don’t shine into the eyes of oncoming motorists.

Some cars have yellow fog lights that are better able to penetrate fog. But they are only better when the fog droplets are smaller than 0.2 microns. In most fog, yellow lights are no better than blue fog lights.

All rights reserved

Published by Chicago Review Press, Incorporated

814 North Franklin Street

Chicago, Illinois 60610

ISBN: 978-1-55652-812-5

Printed in the United States of America

5 4 3 2 1

Library of Congress Cataloging-in-Publication Data

Sobey, Edwin J. C., 1948–

A field guide to automotive technology / Ed Sobey.

p. cm.

Includes index.

ISBN 978-1-55652-812-5

1. Automobiles—Popular works. 2. Mechanics—Popular works. I. Title.

TL146.5.S63 2008

629.2—dc22

2008046620