Newton’s Corpuscular Theory:

..... Light is particles (corpuscles)

........ Evidences:
.......... Light travels through a vacuum
.......... Reflection, (light bounces off of mirrors)
.......... The photoelectric effect, (light kicks electrons out of atoms)
.......... Exerts force (pushes comets’ tails).

Huygens' Wave Theory:

..... Light is waves:

........ Evidences:
.......... Reflection (waves reflect, too)
.......... Refraction (bending of waves)
.......... Diffraction (spreading out of waves)
.......... Interference (waves cancelling and reinforcing)
.......... Doppler Effect (change in color with relative motion)
.......... Polarization (making waves vibrate only in one direction)

Maxwell's Equations show that light is composed of TWO Vectors at right angles to each other: The Magnetic Vector and the Electric Vector.

Max Planck gives us the Quantum Theory that states that light is composed of bundles of energy called Photons.

Sources of Light:

Incandescence-- heated objects give light
..... Stars are plasma, ionized gases at 6000^oC at their surfaces.

..... Arc light. The carbon electrodes are electrically heated to 4000^oC!

..... Light bulbs. The tungsten filament is electrically heated to 4000^oC.

..... Chemoluminescence (chemical reactions producing light)

..... Gas electric discharge (neon signs). High voltage ionizes the gas in the tube.

..... Triboluminescence (crystal deformation, lifesavers)

..... Fluorescence (changes UV into visible light). These minerals are blah in white light:

..... Fluorescent lights: Ultraviolet light emitted by high voltage causes the phosphorescent coating on the tube to emit visible light.

..... Phosphorescence (absorbs light and reradiates it). Things that glow after a light is shown upon them.

..... Sonoluminescence (sound shock waves emit light)

..... LASER: (Light Amplification by Stimulated Emission of Radiation)