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Life, universe and everything

Imaginary colors

Here’s what my very geeky boyfriend told me and once I actually understood it [the 20th time he explained it] found it super awesome.

We detect color through the cone cells which are the photoreceptors (sensitive cells) of the human eye. These cells are sensitive to the wavelengths of light that the objects reflect.

There are different types of cone cells in the eye, each sensitive to a certain range of wavelengths: the S cells are sensitive to Short wavelengths, the M cells are sensitive to Medium wavelengths and the L cells are sensitive to Long wavelengths.

These three types are also referred to as Blue, Green and Red respectively. The cells sensitive to Blue are Short because blue light has a short wavelength (~400nm) as opposed to red light which has a longer wavelength (~600nm).

Below is the response curve of cone cells on the Y axis and the wavelength in nm on the X axis.

You can see there is an overlap of the spectrum that excites the Blue cells with the one that excites the Green cells for example.


Therefore a greenish-blue light will excite both Blue and Green cells but Red cells not that much.

There is no color in the real world that would excite only the Green cells and not the Red, or only the Red and not the Blue, and so on.

The space of colors that we can perceive is actually the colored area in the light below. A color that would be situated outside this area cannot be perceived. The upper-most point of the triangle would indicate a purely green color. That point is not on the graph, therefore we cannot perceive it.


Note however that we can perceive almost pure red because there is a portion of red wavelengths (near 700nm, see 1st graph) where there is almost no green.

BUT we can trick the cone cells and get closer to pure colors.

If you look at a completely red image for 30” until the Red cells are saturated and get tired and if immediately you switch to a completely green image you will see an “almost pure green” without any contaminating yellow hue.

I just tried it and it’s amazing! I’ve made a presentation with 2 red and green slides so you guys can experiment.

To view the presentation if you don’t have Google Docs:
– click on the rectangle in the lower bar of the presentation frame (after the Slide …/4 box)
– in the new window click “View published presentation in a new window”
– click on the grey bar with the arrow on it (on the right of “Print slides” to view the presentation Full Screen)

Have fun!

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