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Essay on Color (continued)

Looking at colored light with the means of physics, we won't limit our view to the tristimulus systems described in para. 1.3 "measuring color sensation".
Instead, we will consider how light energy is distributed across the various wavelengths, i.e. across the "spectrum" (or, at least, its visible part).

2.1 Spectral Range of the Eye's Sensitivity
We know quite a broad range of electromagnetic waves. The visible portion is but a very narrow section out of this broad spectrum:

    fig.2.1-a: visible part of el.magn. spectrum (13 kByte)

Within this narrow range, people have measured how the sensitivity of the eye varies with wavelength. (By the way, this made evident how neatly evolution has optimized eye spectral response to the sun's spectral emission, the latter here represented by Planck@5500K):

    fig.2.1-b: V(lambda) (13 kByte)

In our context, this is a rather rough measurement: considering just "lightness" without color.

You already know that color sensation is linked to the different spectral sensitivty characteristics of the three cone types in our retina as shown in fig. 1.2-c of para. 1.2 Neurology.
This way, we see red colors at the long-wavelength end of the visible spectrum. Proceeding to shorter wavelengths, the colors orange - yellow - green - blue - violet are following.

All this sensitivity is limited to the wavelength range of about 380 to 780 nanometers. Adjacent shorter wavelengths are called "ultra-violet" (UV); adjacent longer ones "infra-red" (IR).

Link List and Literature

Subject used in source
el.-magn. spectrum fig. 2.1-a colour-control
V(lambda) fig. 2.1-b V(lambda)-data taken from:
DIN 5031 T.3 (Maerz 82) Tab. 2

Continued: 2.2 Colorless Light   Contents of entire essay   Contents of entire web site

Last modified Nov. 26th, 2004