2 The Physical Basis of Colour

Some Definitions

light (CIE)

• http://eilv.cie.co.at/term/659

• "1. characteristic of all sensations and perceptions that is specific to vision. 2. radiation that is considered from the point of view of its ability to excite the human visual system". (An associated note suggests that "when necessary to avoid confusion between these 2 meanings the term "perceived light" may be used in the first sense").

• Thus in CIE terminology the word "light" can be used either for the range of wavelengths of electromagnetic radiation visible to humans or for the visual experience (usually) evoked by these wavelengths. In this sense the expression "visible light" is redundant because all light is by definition visible, but note that alternative conventions common among astronomers and physicists equate "light" with all electromagnetic radiation, or include ultraviolet and infrared "light" but seem to draw the line at radio waves, microwaves, X rays and gamma rays.

Websites and Videos

Tour of the electromagnetic spectrum (NASA Science)

• https://science.nasa.gov/ems/

• Excellent series of web pages with videos and linked pdfs explaining the full range of electromagnetic radiation from radio waves to gamma rays, but note the astronomers' disposition to call all of these "light".

Physclips (UNSW)

• https://www.animations.physics.unsw.edu.au/light/nature-of-light/index.html

Causes of color (Michael Douma, Curator)

• http://www.webexhibits.org/causesofcolor/

• The first three sections are based on Kurt Nassau's The Fifteen Causes of Color. (Parts of the fourth section are much less reliable).

ColorBasics - Color theory for the layman

• http://www.colorbasics.com/

• One of the earliest (1996-) websites aiming to provide a simplified explanation of colour science for readers lacking a scientific background. Includes entries relevant to many categories on this site.

Nassau, Kurt, The physics and chemistry of color : the fifteen causes of color (1983)*

• https://archive.org/details/physicschemistry0000nass

• Book on which the Causes of Color website (above) is based.

Mainly on colour (Dietrich Zawischa, English and German)

• https://www.itp.uni-hannover.de/fileadmin/arbeitsgruppen/zawischa/static_html/origins.html

• https://www.itp.uni-hannover.de/fileadmin/arbeitsgruppen/zawischa/static_html/strangeContent.html

A brief organized list (Brian Wandell)

• https://web.stanford.edu/group/vista/cgi-bin/wandell/a-brief-organized-list/

• Concise list of key facts about colour vision and its physical basis.

Why does light slow down in water? (Don Lincoln, Fermilab)

• https://www.youtube.com/watch?v=CUjt36SD3h8

The original double slit experiment (Veritasium. 2013).

• https://www.youtube.com/watch?v=Iuv6hY6zsd0

The history and science of color temperature (Filmmaker IQ)

• https://www.youtube.com/watch?v=3HnhIRPLWsM

• One of a number of reasonably reliable videos on colour for films on the same channel.

Colour theory in two minutes (Stephen Westland)

• https://colourware.org/2018/06/24/1-colour-and-wavelength/

Lighting

Lights and Shadows (Bartosz Ciechanowski)

• https://ciechanow.ski/lights-and-shadows/

• Superb introduction to light and shade using interactive demonstrations

Handprint (Bruce MacEvoy)

• https://www.handprint.com/HP/WCL/color1.html#light (light: the spectrum we can see )

• https://www.handprint.com/HP/WCL/color3.html#measuringlight (measuring light and color)

• https://www.handprint.com/HP/WCL/color3.html#photounits (the spatial geometry of light)

The dimensions of colour, Part 2, Basics of light and shade (David Briggs)

• http://www.huevaluechroma.com/021.php

• http://www.huevaluechroma.com/022.php

• http://www.huevaluechroma.com/023.php

Hanrahan, P. and Kruger, W., Reflection from layered surfaces due to subsurface scattering (1993)

• http://www.cs.princeton.edu/research/techreps/TR-409-93

• Paper referred to in Basics of Light and Shade above.

Physically Based Rendering:From Theory To Implementation (Matt Pharr, Wenzel Jakob, and Greg Humphreys)

• https://www.pbr-book.org/

• Outstanding free online book describing in detail the theory and practice of photorealistic rendering systems

Physically Based Rendering in Filament (Romain Guy and Mathias Agopian)

• https://google.github.io/filament/Filament.html

Online and Downloadable Programs

f.luxometer

• https://fluxometer.com/rainbow/#!id=iPad%20Pro/6500K-iPad%20Pro

• Displays spectral distributions for numerous devices, illuminants and natural and artificial light sources.

Spectrashop (Robin Myers):

• http://rmimaging.com/spectrashop.html (Windows/ Mac)

• https://www.chromaxion.com/spectral-library.php spectral library as zip files)

• SpectraShop is a program for measuring, analyzing and storing visible light spectra. It can measure spectra directly with various instruments, or import data from other programs. In demo mode the program will not measure, save or export data, but it will open and display spectral files from the large array provided.

Blackbody Spectrum (PhET Interactive Simulations, University of Colorado, Boulder)

• https://phet.colorado.edu/en/simulation/blackbody-spectrum

Reflection and Two materials (Brown University)

• http://www.cs.brown.edu/exploratories/freeSoftware/catalogs/color_theory.html (Online/Windows/Mac)

• Series of applets for demonstrating colour theory, such as the interaction of spectral distribution and reflectance curves on reflected light (seem very difficult to get working on modern browsers). Other applets on the page relate to colour vision and additive mixing.

*Titles marked with an asterisk were published between twenty-five to one hundred years ago and are available to read online for an hour at a time or be borrowed (subject to a wait list) for 14 days, but can not be downloaded.

Colour in Nature

The Colors of Life (Julien P. Renoult and Bernard Valeur )

• https://www.chemistryviews.org/details/ezine/9064741/The_Colors_of_Life.html

How Birds Make Colorful Feathers (Bird Academy)

• https://academy.allaboutbirds.org/how-birds-make-colorful-feathers/

Minnaert, Marcel G.J., The nature of light & colour in the open air (1954)*

• https://archive.org/details/natureoflightc00mmin

Williamson, Samuel J., Cummins, Herman Z., Light and color in nature and art (1983)*

• https://archive.org/details/lightcolorinnatu00will

Lynch, David K., Color and light in nature (1995)*

• https://archive.org/details/colorlightinnatu0000lync