cs781 - Colour for Computer Graphics - Winter 2012

Course Notes

Lecture 2 - Light, Sources of Light

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What is Light?

Particles and forces

  1. gravity, mass, graviton (hypothetical) holds together planets up to galaxies
  2. electromagnetic force, electro-magnetic charge, photon holds together things with charge: atoms, molecules, solids and liquids, biology, computers
  3. weak nuclear force, isospin, V and W bosons
  4. strong nuclear force, colour, gluons holds together baryons: protons, neutrons

Electromagnetic Radiation

Electromagnetic radiation (the photon field) is the carrier of the electromagnetic force. Like all the fundamental fields it can be present at a wide range of energies and wavelengths.


A particular energy range of electronic radiation, the range to which human photoreceptors are sensitive, is called light. Its energy range is

For comparison, at room temperature (~290 K) the peak of the photon distribution is

A few interesting things to consider about light.

Particles and Waves

Properties of Light

The spectral power distribution ignores the phase and polarization of the light. According to the current state of the art, visual properties of light, inter alia its perceived colour, depend only on the spectral power distribution of the light.

How is Light Created?

Light and Biology

In the current era life on earth is inseparable from light. Why?

High energy, within limit, photons are preferred to low energy ones because its hard to collect several photons that add up to the exact energy that, say, an electornic transition requires.

A side point.

Biology without Light

This seems to be where life started

Biology with Light

Light is the primary source of energy

Implications for Vision

Why does life need vision?

  1. To capture the energy of photons
  2. To perceive things at a distan

Where did vision come from?

What was the first vision?

Where Does Colour Come From

How does bacterial purple work?

  1. a molecule accepts a photon of a specific wavelength (energy)
  2. new configuration enters into a chemical reaction

Photoreceptors in the human eye work exactly the same way,

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