As the sociopathic kids burning insects with a magnifying glass later growing up into the world's serial killers found out. Light itself is pretty nebulous and not easily observable unless concentrated into a beam by a prism or otherwise used to illuminate an area where there is a notable absence of it.

It acts as both a particle and a wavelength and can change between either state when unobserved. These facts have been proven in an experiment conducted where light was sent between two holes. As predicted, the light split up into two separate rays which illuminated the background beyond the two holes. This experiment was repeated in different ways under different circumstances and found that light, like electricity or water, prefers to follow the path of least residence to its destination. That appeared to confirm that it was both a wavelength and particle as scientists. They also noticed that the Light could change depending on whether it was being observed or not. Pretty strange stuff to say the least. Light, or matter that behaves in a similar manner to it can also be trapped inside an inverted prism and bounced around indefinitely while retaining most of the energy it had, which people suspect is the key behind getting fusion reactors to work.

All and all, some pretty interesting stuff when you take the time to look at the physics behind light itself.