New trends in physics teaching, v.4; The ... - unesdoc - Unesco

Colour
200
150
(I]
U C
; 1 0 0
E
m
a,
2
U
- m
a,
[I
50
0
400 500 600 700
Wavelength / n m
Tristimulus Values of Equal Energy Spectrum
Figure 8. Spectral tristimulus values, modified to provide the CIE xhyh and zh values.
at small, equal wavelength intervals as before but using these new values of the spectral tristimulus
curves, we obtain X = k2h Eh ?A, Y = k2h Eh yh, Z = kZh Eh FA, where k is a scaling constant,
and hence obtain new CIE tristimulus values for our test lamp. These values should be the same
as X, Y, 2, obtained from our experimental values for (r) (b) (g).
A discussion such as this showing the development of the chromaticity diagram often appears
somewhat confusing. However, the important points concerning the diagram can be quickly
summarized without understanding how it was obtained.
The appearance of any colour, of whatever nature, exclusive of its brightness, can be represented
by two quantities, x and y, plotted on a two-dimensional graph called the chromaticity diagram;
these co-ordinates must lie within a figure defined by the spectral hues. Illuminants having
different spectra can have the same x and y values.
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