In the 1670's, Christiaan Huygens, proposed light traveled as a wave. If light travels as a wave it have wave like characteristics. And it does.
"Christiaan Huygens" by Caspar Netscher,Museum Hofwijck, Voorburg Public Domain, https://commons.wikimedia.org/w/index.php?curid=3472319 Accesses 02/15/2016.
If the shadow of an object is far away from the object, then the edges will be fuzzy.
In 1899 Lord Rayleigh (pronounced ray-ley) explained that the sky is blue because the water molecules in the air are the correct size to scatter the blue wavelengths of light the most. This gives the sky its blue appearance. At sunset and sunrise the sun's rays travel through more of the Earth's atmosphere than at midday. At these times the blue light is completely scattered and the remaining parts of the light spectrum begin to scatter
Sunsets and sunrises are red because of the blue and green is scattered "out" and the longer wavelength red is left.
image: http://www.goodfreephotos.com/places/wisconsin/kettle-moraine-south/wisconsin-kettle-moraine-south-big-red-sunset.jpg.php accessed 02/15/2016
Newton comes along about 15 years later and says light is a particle.
Portrait of Isaac Newton in 1689 (age 46) by Godfrey Kneller By Sir Godfrey Kneller - http://www.newton.cam.ac.uk/art/portrait.html, Public Domain, https://commons.wikimedia.org/w/index.php?curid=37337 Accessed 02/15/2016
His evidence? Light reflects off of smooth surfaces at an angle equal to the incident angle. (This is the law of reflection.)
But some light bounces of the boundary of a smooth water surface while other light particles pass into the water. Newton's description was that the particles are confused and have a "fit." (By fit he means a temper-tantrum.) Not a good explanation.
Thomas Young comes along and does his famous double slit experiment and the scientific
community believes light is wave... again. The scientific community is split until 1905 when Einstein says light is a wave or a particle depending on how you measure it. When light is traveling it behaves like a wave. When it impacts a surface that does not allow it to penetrate, it behaves like a particle. (This is a general simplification.)