Early Concepts of Light (Wrong!!)

• Ancient Greece– Some believed light consisted of particles that

entered the eye to produce sight– Plato & Socrates believed that eyes emitted

“streamers” making contact with objects, allowing sight

Who got it right?

• Greek Philosopher/Scientist, Empedocles, was the first to teach that light traveled in waves– Wave Theory was accepted by nineteenth

century

Instantaneous or Finite Speed?

1675 - Danish Astronomer, Olaus Roemer was the first to demonstrate that light traveled with a finite speed!!!

How Fast?

• American Physicist, Albert Michelson (1880)

• Winner of the 1907 Nobel Prize

• Determined speed to be 299,920 km/s

Light &

Electromagnetic Waves

Light Fundamentals

• Light - An Example of a Transverse Wave

• Speed of Light 3.0x 108 m/s

Light Fundamentals

• Light is electromagnetic radiation

• Light is simply a form of Energy that travels as a transverse wave.

• All electromagnetic waves travel at 3.0 x 108 m/s

• More on the Electromagnetic Spectrum

Light Sources

• Light Sources– luminous vs. illuminous

• emits light vs. reflects light

Light Fundamentals

• Inverse-Square Relationship– The illuminance of a body varies inversely with

the square of the distance from the light source

• Luminous Flux, P – rate at which light is emitted (measured in

lumens, lm)

• Luminous Intensity– the luminous flux that falls on one square meter

Light Fundamentals

• Illuminance, E – The illuminous Intensity of a surface

• Measured in lumens per square meter or a lux, lx)

• E = P / 4r2

Light and Matter

• Transparent Materials– Materials that allow

light to pass through them in straight lines.

Light and Matter

• Translucent Materials– Materials that transmit

light but do not allow objects to be seen clearly through them.

Light and Matter

• Opaque Materials– Materials that absorb

or reflect light without remission and therefore allow NO light to pass through them.

– Opaque materials often create shadows where light can not reach

Light and Matter

• Polarization of Light– The aligning of vibrations in a transverse wave, usually by filtering out

waves of other directions

– 3D movies… and other tricks… Demos