Color Physics @Hampshire, Day 18

On Day 18 we

  • Discussed the pieces students drew/painted over the course of the last three days

A halftone exercises with watercolors by Madeleine Perreault.A halftone exercise with watercolors by Madeleine Perreault.


The effects of additive mixing. Piece by Sara Young, looks grey from far away, but up close it is a colorful mixture.
  • Practiced how to determine the spectral composition of reflected light from the spectral composition of incident light and the reflectance curves of the surfaces.
Given date for a sample problem for which students used the incident intensity distribution and the reflectance curve to find the intensity distribution of the reflected light.

Color Physics @Hampshire, Day 14

On day 14, in preparation for an activity of making holograms, Prof. Wirth gave a mini lecture on interference of light, its use in early color photography, and its application to holography.

After that, we continued our exploration of subtractive mixing with filters.  Students worked through a worksheet in which  they had to answer quantitative and qualitative questions. Among other things, students

  • Made predictions about the intensity distribution of transmitted light given a wide-spectrum white light incident on ideal filters with a variety of transmittance curves, and compared them with observations.
  • Made predictions about the intensity distribution of transmitted light when colored light is incident on ideal filters with a variety of transmittance curves, and compared them with observations.
  • Sketched the transmittance curves for a combination filters.
    We worked on transmittance curves for multiple filters.
    We worked on transmittance curves for multiple filters.


  • Looked at the real transmittance curves of our filters to understand why not all of the light is blocked by overlapping cyan, magenta, and yellow filters.

At the end, we went over all of the answers as a class.

Light passing through overlapping filters
Subtractive mixing with filters.


Color Physics @Hampshire, Day 10

After reviewing the concepts of wavelength, amplitude, and frequency in general, we discussed the special case of electromagnetic waves and the electromagnetic spectrum. The key ideas covered were the

  • Inverse relation between the wavelength and frequency of an electromagnetic wave.
  • Intensity of a wave and its relation to the amplitude of the wave.

In a lecture-heavy portion of the class, we went over how different properties of an EM wave in the visible spectrum correlate with the hue, saturation, and brightness of the perceived light.  I used very good slides developed by Geoff Boynton at the University of Washington.

Geoff Boynton's slide on the relation of the width of the spectral intensity-distribution of light and the perceived saturation.
Geoff Boynton’s slide on the relation of the width of the spectral intensity-distribution of light and the perceived saturation.

We introduced the spectral intensity-distribution graphs for light sources and the distinction between spectral colors and non-spectral colors, but also reviewed additive color mixing in the context of the intensity-distribution graphs. We touched on the relevance of additive mixing to the pointillist painting movement developed by Seurat.

Students then used hand-held spectrometers to determine the intensity-distribution for the red, green, and blue LED’s we used in additive mixing exercises earlier in the semester.  We also tried to determine the spectrum of the mixture various pairs of lights. This was tricky because of the light pollution in the room and the fact that the light from two LED’s was coming from different angles and scattering within the spectrometer.  

Students measured and recorded the intensity distributions of light from LEDs.Students measured and recorded the intensity distributions of light from LEDs.

Some of the students got to start playing with color filters and explore their absorption spectrum, but more formal introduction was left for the following class.

Color Physics @Hampshire, Day 8

On Day 8, we investigated transverse waves.

  • Students did some prep work at home by playing with a PhET interactive simulation  exploring qualitatively various properties of a wave on a string, and recording their observations.

    PhET Interactive Simulation on Waves
                                                       PhET Interactive Simulation on Waves
  • In class, we introduced a transverse sine wave and students worked in groups to come up with a comprehensive list of properties of a sine wave needed to describe it to grandma. This led us to the concepts of amplitudewavelengthperiodfrequency, and speed, as well as their respective appropriate units. We subsequently practiced finding the values of these properties for three animated waves I made using Grapher.
  • At the end of the class, as a taste of things to come, students briefly made waves with slinkies.
Students making waves with slinkies.
       Making waves with slinkies.

Color Physics @Hampshire, Day 6

On Day 6, we began to unpack the statement that light is an electromagnetic wave, leaving the particle nature of light for a later discussion.

A styrofoam sphere prickled with toothpicks.
A toy model of the electric field lines of a spherically symmetric electric charge made of styrofoam sphere and toothpicks.
  • We discussed electric charge and electric force.
  • We introduced the concept of electric field!
  • We learned about two ways of visually representing the strength and the direction of the electric field, one with arrows at various points, the other with field lines. To get a better sense of the spatial distribution of the field, students built with styrofoam balls and toothpicks 3D models of the electric field of a spherically symmetric charge.
  • We worked on conceptual problems testing students’ understanding of the above concepts.

Color Physics @Hampshire, Day 5

On Day 5, we were familiarizing ourselves with notation and problem-solving strategies.

  • We completed more examples of units conversions and scientific notation.
  • We practiced problem-solving with examples relating speed, distance, and time 

We ended the class by deflecting a stream of water with an electrically charged balloon as a segue to the discussion of light as an electromagnetic wave!

Color Physics @Hampshire, Day 4

Day 4 consisted of wrapping up the discussion of HSB, introducing the RGB model, and setting the groundwork for the upcoming discussion of physics.

  • Review of of Hue, Saturation, and Brightness 
    • HSB cylinder
  • Additive color mixing: We organized our observations of mixing of colored light from the previous class and introduced the RGB color model.
    • Primary colors in additive mixing
    • Complementary colors in the additive system
    • RBG color model
    • RGB cube
  • Measurement in physics:
    • What is science?
    • Units and unit conversions
    • Scientific notation and orders of magnitude. We watched Powers of Ten to get a better sense of what different powers of ten mean in terms of different scales, so that we can assess our answers to numerical problems.
A scene from Powers of Ten™
Powers of Ten™

Other Resources: A student pointed me to an interactive catalog of objects of a vast range of sizes, organized by powers of ten