The Physical Stimulus for Vision
u Light
l A form of Electromagnetic Energy
l Two Complementary Descriptions
u Particle - Photon is unit of light.
u Wave - like a wave in ocean
Electromagnetic spectrum
gamma - 10-14 - 10-12
x-rays - -- ~10-9
Ultraviolet -- ~760 nm (>10-7)
°     Visual 760-380 nm
Infrared <10-6 - ~10-3
radar -- 10-1
radio bands > over a mile