Almost half of the brain is dedicated to visual info processing. Humans used to believe that light was emitted by objects and that the light travelled through the ether in straight lines. Dual theory of light: theory that light is composed of particles known as photons that have wave-like motion when they travel. Remains the cornerstone of our current understanding of light. Energy is radiated in the form of a wave, comes from motion of oscillating charged particle (photon). The movement of photons through space produces an oscillating electric and magnetic field (they move together in the same direction as photon). So, electromagnetic radiation is made up of 2 moving wave forms, electric and magnetic field (linked together). The 2 fields are perpendicular to each other and they fluctuate in intensity together. This basically represents the waves that move through space. Wavelength is one cycle (which later repeats itself).