then appears separately. This effect is
called a spectrum. A rainbow is a type of
spectrum. When raindrops make a rainbow,
they are acting like prisms.
Light and Sight
People see an object either because it
gives off light or because the object
reflects, or bounces back, light. For
example, people see the sun because it
gives off its own light. But people see the
moon only because it reflects light from
the sun.
Most objects absorb some light and
reflect some light. The reflected light is
the color of the object. If an object does
not reflect much light, the light passes
through it. This type of object is called
transparent, or see-through. By contrast,
Some small sea creatures called tunicates
give off light naturally.
148 Light BRITANNICA STUDENT ENCYCLOPEDIA
mirrors reflect almost all the light that
hits them.
Light and Life
Light is very important to life on Earth.
Using the energy of sunlight, plants
combine a gas in the air called carbon
dioxide with water in the soil. Through
this process, called photosynthesis,
plants make their own food. People and
other animals then use plants for food.
As plants make food, they also give off a
gas called oxygen. People and other animals
need oxygen to stay alive. Sunlight
helps animals to grow, too. It causes the
body to make vitamin D, which the
body needs to make bone.
#More to explore
Color • Energy • Mirror
• Photosynthesis • Prism • Rainbow
• Sun
Lighthouse
Ships rely on lighthouses to warn them
of danger and to guide them to land or a
harbor. A traditional lighthouse is a tall,
rounded tower on land near a coast.
Modern lighthouses may be on land or
they may be a platform in the sea. The
main feature of all lighthouses is a bright
light.
Lighthouses used to be operated by a
lighthouse keeper who lived in the
building. Many modern lighthouses
have automatic lights that are operated
by remote control.
Types of Signals
The earliest lighthouses used burning
fires as a source of light. Later versions
used lanterns holding groups of large
candles, or lamps that burned oil or gas.
Today the standard source of light is an
electric lamp. A special lens focuses the
light into a beam that can be seen far
away. The lamp and the lens turn so the
beam shines in all directions.
Most objects reflect, or bounce back, colored
light. Mirrors reflect nearly all the light
that hits them. Windows are see-through
because they do not reflect much light.
The Thomas Point Lighthouse sits in Chesapeake
Bay, south of Annapolis, Maryland. It
was built in the 1800s.
BRITANNICA STUDENT ENCYCLOPEDIA Lighthouse 149
In bad weather, light cannot always be
seen. Lighthouses then must use other
methods to signal ships. One method is
sound. Lighthouses once used cannons
or bells to warn ships. Today the most
common sound device is the foghorn.
Modern lighthouses also send out radio
and radar signals to passing ships.
Lightships and Buoys
Lightships and buoys are movable
devices. They are used in places where
lighthouses cannot be built. Modern
lightships are small ships equipped with
lights, a foghorn, and radio devices.
Buoys are smaller floating objects. They
provide light to navigators as well as
other information through their color
and shape.
History
The first true lighthouse may have been
one that was built in about 280 BC in
Egypt. The Phoenicians, Greeks, and
Romans also built lighthouses during
ancient times. As shipping increased in
Europe around AD 1100, construction of
lighthouses also increased.
In 1759 an English engineer named
John Smeaton designed a new type of
lighthouse. It became a model for most
lighthouses that followed. The lighthouse
was built from interlocking blocks
of stone instead of wood. This strengthened
the structure so it could withstand
powerful waves.
Lightning Bug
..see Firefly.
Lilongwe
Population
(2008 estimate)
669,020
Lilongwe is the capital of Malawi, a
country in southeastern Africa. The
country’s president and lawmakers work
in Lilongwe. Malawi’s highest court
meets in the city of Blantyre. Blantyre
and Lilongwe are the two largest cities in
Malawi.
The two centers of Lilongwe are called
Old Town and Capital Hill. A nature
sanctuary separates the two areas.
Farmers from surrounding areas sell
their crops in Lilongwe. Malawi’s main
crop is tobacco. Large amounts of
tobacco are traded in Lilongwe. Many
people in the city work in government
offices, schools, or hotels.
Great Britain took over what is now
Malawi in the late 1800s. The British
founded Lilongwe in 1902 as a government
post. Malawi became an independent
country in 1964. Lilongwe became
the capital in 1975. It was chosen to be
the new capital because it lies in the
center of Malawi.
..More to explore
Malawi
The U.S. state
of Maine is
famous for its
lighthouses.
More than 60
lighthouses
stand on its
rocky shores.
150 Lightning Bug BRITANNICA STUDENT ENCYCLOPEDIA
Lily
Lilies are plants that are prized for their
beautiful and fragrant flowers. There are
about 80 to 100 species, or kinds, of
true lily. They belong to a much bigger
plant group called the lily family, which
contains about 4,000 species. The lily
family includes tulips, hyacinths, and
