Maxwell's House 4

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Maxwell's House
Episode 4

It's All In Your Head: Part 2 - How Colour Works

Part 1 discussed how the human eye responds in general. This show relates to how the eye responds to colour. The response is all in the brain, a figment of our imagination. We can measure with physical instruments the physical stimuli that causes our eye to see colour. There are some very interesting twists as to how these stimuli are interpreted by our brains.


There were no guests on this episode.


Colour Spectrum

Most people think that color is just a certain wavelength of electromagnetic radiation. This falls in between infrared, ultraviolet, x-ray, shorter wavelengths & radio waves at longer wavelengths. The slide shown depicts wavelengths of 400-700 nanometers of electromagnetic energy that the human eye sees as colour.

Imaginary Colours

There are some imaginary colours that can be created in the eye that are not stimulated by a single wavelength of light.

Mapping The Human Response

An experiment done in the 1930s resulted in the ability to chart the response of the human eye; a red, green and blue response of the three kinds of cones in your eye showed that the red and green response overlaps heavily. When the red-green response overlaps too much red-green color blindness occurs. (you would still see yellows and blues). The experiment involved a prism (which divides white light into individual wavelengths of light that we see in the spectrum), a spectral colour through a slit onto a screen and a red green and blue light source that the observer could dial the intensity. The experiment restricted the point of view of the observer to only 2 degrees eliminating the fovea (the central part of the eye where the really sharp vision is).

You only have sharp vision in the fovea, the size of a dime length. When moving the fovea around a scene, the eye flicks around when your reading, etc and assembles a high definition image in your brain.

The Paint Chip Effect

In 1964 the experiment was revisited where the C.I.E tried to eliminate more of the retina, opened up the slot in the baffle and re-plotted the response to a ten degree observer. This was compared to the 2 degree response. The amazing discovery was that the response was different. This explains why comparing little colour swatches/colour chips from the paint store to your drapes before you paint the wall results in a different impression of the colour after you paint. This is because the colour is filling a large part of your vision.

Colour is An Illusion in Your Brain

The eye responds to different spectral stimuli but the brain sees the same colour. A yellow object such as a banana as seen on the Lab with Leo episode 63 that only reflected yellow light - 575 nanometers - this would sit right at the overlap of the red and green response of the cones in the eye. In the brain, red and green is stimulated and blue is not stimulated so it sees yellow. However, the exact same response can be achieved by putting out a red and a green - 555/600 nanometers; mixing these two sources of light will result in the brain seeing the exact same yellow colour. Thus two different spectral stimuli make your brain see yellow; one, a single frequency, the other, a mixture of red and green.

Magenta, The False Colour

Mixing red, green and blue results in white. Red and blue mixed results in the brain seeing a the colour magenta which is neither red nor blue. This magenta colour that the brain sees has no single frequency in the spectrum that can cause your brain to see it. Two colours in your brain at once creates a new third colour that doesn't exist in the spectrum. Unlike the yellow which has a frequency, there is no frequency for magenta. You can have a true yellow and a mixed yellow but you can't have a true magenta. There is no such thing as a single frequency magenta. Sending a red and blue signal to the eyes stimulates the red and blue cones. The brain sees a single colour we call magenta. There is, however, no single frequency that can be sent to your brain that would cause you to see the same thing. Magenta is an imaginary colour that only occurs in your brain. There is a host of other imaginary colours in the side of the colour circle when green is subtracted from the red-green-blue mixture. There is no magenta if you put white light through a prism to create the rainbow effect.



Notable Comments

  • Leo and Ray experimented with Adobe Connect screen sharing technology. The show was billed as a mini Maxwell's House due to Leo spending 45 minutes trying to get his connection working.
  • Reminder: email to request topics for Ray to discuss in depth. requested show topics include: How a pin-hole camera works, what are optical computers? what are quantum computers?
  • Ray mentions he is excited about the red camera release. Leo explains that the red camera is a 4K camera, a double high def camera that had just started shipping in limited quantities at the time of recording. Leo mentions that Oakley, an optical expert, then had two new devices, a Scarlet and an Epic that will shift the paradigm on Digital SLRs forever.
  • Ray mentions that he has a 'juggling friend' whose husband is writing the firmware for the Red Camera. Leo suggests a future show topic: The Physics of Juggling and how we transmit juggling patterns over the internet.

Production Notes

  • Recorded Date: November 13, 2008
  • Release Date: November 13, 2008
  • Duration: 20:41
  • Log line:
  • Edited by:
  • Notes: