The peak position of the spectral density for blackbody radiation is given by the Wien displacement law. Within introductory physics materials it is often stated, or implied through example, that the color of the light emitted from a blackbody, such as the Sun, can be ascertained from knowledge of the position of that peak in the spectral density. Such a conclusion is at best incomplete, may be misleading, and in many ways can be considered to be wrong. Here these claims are addressed and a method for introducing and better understanding spectral density is presented. For concreteness, the discussion centers around the solar spectrum, which is often used as an example in physics and astronomy classes.

1.
For more
information
,
see L.
Gunther
,
The Physics of Music and Color
(
Springer
New York
,
2012
).
2.
H.
Fletcher
and
W. A.
Munson
, “
Loudness, its definition, measurement and calculation
,”
J. Acoust. Soc. Am.
5
,
82
108
(
1933
).
3.
E. J.
Heller
,
Why You Hear What You Hear
(
Princeton University Press
,
Princeton, NJ
,
2013
).
4.
A more correct statement would be that white light consists of a continuous range of monochromatic electromagnetic waves, each one of which will be perceived as having a color when viewed separately, and this collection of colors will include all of the colors of the rainbow.
5.
See also A. Cortel
, “
Simple experiments on perception of color using cardboard turbines
,”
Phys. Teach.
42
,
377
(
Sept.
2004
).
6.
G. S.
Smith
, “
Human color vision and the unsaturated blue color of the daytime sky
,”
Am. J. Phys.
73
,
590
597
(
July
2005
).
7.
P. L.
Pease
, “
Resource letter CCV-1: Color and color vision
,”
Am. J. Phys.
48
,
907
917
(
Nov.
1980
).
8.
See,
for
example
,
E. E.
Anderson
,
Modern Physics and Quantum Mechanics
(
Saunders
,
Philadelphia
,
1971
).
9.
B. H.
Soffer
and
D. K.
Lynch
, “
Some paradoxes, errors, and resolutions concerning the spectral optimization of human vision
,”
Am. J. Phys.
67
,
946
953
(
Nov.
1999
).
10.
By comparison with extraterrestrial data, representing the spectrum above the atmosphere, from ASTM G173-03(2012), “
Standard Tables for Reference Solar Spectral Irradiances: Direct Normal and Hemispherical on 37° Tilted Surface,” ASTM International
, https://www.astm.org/Standards/G173.htm.
11.
With wavelength in nm, temperature in kelvin, and frequency in terahertz, E(λ) in W/m2/nm = c15 [exp(c2/λT) – 1], λ = c0/f, and E(f) in W/m2/THz = c0E(λ)/f2, where c0 = 2.997 × 105, c1 = 1.439 × 107, and c2 = 8.418 × 1015.
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