CS781 - Colour for Computer Graphics - Winter 2009

Lecture 2

Light, Sources of Light

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 (the photon field) is the carrier of the electromagnetic force. A particular energy range of electronic radiation, the range to which human photoreceptors are sensitive, is called light. A few interesting things to consider about light.

Particles and Waves

Properties of Light frequency:

The spectral power distribution ignores the phase and polarization of the light. From it we can deduce properties of light that depends only on the spectral power distribution of its energy, which includes its perceived colour.

How is Light Created?

Light and Biology

In the current era life on earth is inseparable from light. Why? entropy continuously increases energy needs to be injected into any system with order injected energy is light. A side point. If the earth is to avoid heating up the amount of energy that arrives must equal the amount of energy that leaves. Light arrives at short wavelengths (high energy photons), and leaves at long wavelengths (low energy photons, or heat)

Biology without Light

The earth is created full of free energy high energy constituents from supernovas gravitational energy transformed into heat and chemical potential

Biology with Light

Light is the primary source of energy light is captured by a molecule that has two states (receptor) an enzyme uses the energy to build a high energy molecule: ATP or a sugar or a fat when the energy is needed

Implications for Vision

Why do we need vision?

need to move toward the light need to move toward creatures whose stored energy I can steal

Where did vision come from?

What was the first vision?

Where Does Colour Come From

How does bacterial purple work?

  1. molecule accepts a photon
  2. new configuration catalyses a chemical reaction
  3. products of the chemical reaction open channels in the cell membrane
  4. eventually enough charge flows to change state of the photoreceptor

Photoreceptors in the human eye work exactly the same way.


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