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Some animals see over a different range than we do and can see either infrared or ultraviolet light.
Light from a point source such as the Sun or a light bulb sends rays, or radiates, outwards in
all directions. Because of this
the amount, or intensity, of light falling on a surface lessens with the square of the distance to
the source. That is why stars
look dimmer than the Sun, even though the stars may be radiating thousands of times more light than our Sun. It also explains why the same light bulb seems brighter when seen close up as opposed to further away.
The light from a source such as a light bulb can be made to shine in one direction. We call it a beam of light. In a torch a reflector is
placed behind the light and a lens in front of it. That produces a single beam of light. In this case the
light intensity stays the same
and is not affected by distance. Searchlights demonstrate this effect very well; their beam of light travels for several kilometres without widening. A laser beam can travel much farther.
(See also: Photon.)
Light-year
The distance that light can travel in a year. It is used to measure distances in space. Light travels
at 300,000km per second. A light- year is about 9,500,000,000,000 km: nine and a half million million kilometres. Astronomers use an even larger unit called the parsec. It is about 3.262 light-years.
Light-year
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