It's a kind of energy called "electromagnetic (EM) radiation" (but this kind of radiation is not harmful, except for an occasional sunburn). There are other kinds of EM radiation too (radio waves, microwaves, x-rays, etc.), but light is the part WE can see, the part that makes the rainbow.
How does light travel?
FAST and STRAIGHT.
About 186,000 miles per second [300,000 kilometers per second], so light from the sun takes about 8 minutes to go 93 million miles [149 million kilometers] to earth. Does this seem SLOW? Well, if you could DRIVE to the sun at 60 mph [100 kph], it would take you 177 years to get there! In one second, light can go around the earth 7 times!
Perfectly straight, until something bends it. The straight paths of light are called LIGHT RAYS.
There are THREE basic ways to control light (these activities require Flash):
Block it ... with something (this makes a shadow)
[This image requires the Flash plug-in]
Reflect it (change its path with a mirror)
This is called a REFLECTION. Click on the image below to see the interactive demo. Demo courtesy of Mr. David M. Harrison, Dept. of Physics, Univ. of Toronto.
Change its direction by making it pass into another transparent material of different density, like glass or water.This is called REFRACTION, and it's how lenses work. Click on the image below to see the interactive demo. Demo courtesy of Mr. David M. Harrison, Dept. of Physics, Univ. of Toronto.
The fine print: There are actually other ways to bend or deflect light, including diffraction gratings and holographic lenses. These depend on the wave nature of light, and are a little more difficult to explain. Scientists have also found that gravity can bend light, but it takes a very large object with strong gravity such as a star to bend light very much, so it's not an effect you see every day!
Light is produced, controlled, and detected in so many ways around you!
... And many more things such as
Did you get them all?