Definition

Absorption is the process by which electromagnetic radiation is converted to another type of energy as it passes through a material. The absorptance of a particular object or instance of material measures its effective absorption, given as a ratio of the total amount of light or electromagnetic radiation that is absorbed compared to the total amount originally incident upon it. The absorptivity of a material is the amount of absorption that takes place per unit of distance light travels within it.

In opaque materials, absorptance is directly related to reflectance and therefore the surface color. Black materials have the highest absorptance values and white materials the lowest. Objects with a discernible colour will fall somewhere between these two extremes. In transparent and translucent materials, the relationship with reflectance is less direct, with colour and transmittance taking over.

Figure 1 - A set of spheres showing the visual effect of different levels of absorptance with different materials.

Opaque materials obviously have the highest absorptance values as transmitted light is completely absorbed almost as soon at it enters. Translucent and transparent materials have lower absorptance values as some of the transmitted light is able to travel all the way through without being absorbed.

The Process of Absorption

When light passes through a material, it interacts with it at a sub-atomic level. All materials – be they solid, liquid or gas – are made up of molecules that contain atoms of one or more elements. These atoms contain varying numbers of protons, neutrons and electrons, with the electrons orbiting a nucleus made up of the protons and neutrons.

When a photon of light collides with an atom, it imparts its energy by changing the orbit of one or more electrons. Each atom can only support a certain range of electron orbit states. If the new state of the electron is supported then the electron will stay in its new orbit, increasing the kinetic energy of the atom which is then dispersed within the material as heat. When this happens, that photon is effectively absorbed.

If the new electron state is not supported, the electron quickly decays back to a supported state, releasing the excess energy as a photon of light. That photon either goes on to collide with another atom or, if it is close to the surface, escapes back out of the material as reflected light.

Different atoms support different ranges of electron states and, as light with different wavelengths contains different levels of energy, the confluence of the two means that some wavelengths will be absorbed more than others depending on the type and distribution of atoms within the material. This gives us the characteristic absorption spectrums of different materials and elements.

Transparent and Opaque Materials

One question that seems to come up reasonably often in this area can be summarised as follows: ‘if reflection and absorption are directly related to color for an opaque object, why do the Fresnel equations for transparent objects not seem to account for colour or absorption in any way?’. I am not sure I have the absolute answer for this one, but I do have an opinion on the subject.

When light is incident on the boundary between two transparent materials, Fresnel equations allow us to calculate the amount that is reflected and transmitted, but they do not include any consideration of the amount absorbed. Also, the equations themselves depend entirely on the refractive index of each material, suggesting that absorption plays no part in the reflected component. Reading further, absorption in transparent materials is only applied to the transmitted component as it travels through the receiving material. Thus, for transparent materials, the maxim seems to be whatever isn’t reflected must have been transmitted.

Fresnel equations do not apply to opaque materials and there is no meaningful transmission component. Thus, the behaviour of incident light is determined by the reflectance and absorptance of the material. In this case, the maxim becomes whatever isn’t reflected must have been absorbed.

Figure 2 - The relationship between reflection, transmission and absorption in transparent and opaque materials.

The difference between the two is simply nomenclature as the fundamental mechanisms are the same in both instances. A photon of light strikes the material boundary and collides with an atom, imparting its energy by changing the orbit of an electron. Depending on the wavelength of the photon and the nature of the atom, the electron either retains its new state (thus absorbing the photon), or quickly decays to its original state, emitting the excess energy as another photon. One of three things can then happen to this new photon. The most likely is that it will collide with another atom and repeat the process. Alternatively, if it is near the boundary surface, it could escape back out and become part of the reflected light component. If, after many previous collisions, it is near the other side of the material, then it could escape out that way and become part of the transmitted component.

In opaque materials, there are simply more atoms that are able to retain their new electron states and therefore effectively absorb all of the photons that enter. In transparent materials, the photons either pass through without colliding with anything or the atomic structure of the material is such that very few electrons retain their new states and the emitted photons mostly travel in the same direction as the refracted light wave. In translucent materials, the atomic structure is such that few electrons retain their new states but the emitted photons travel in any direction. This mans that the distribution of both reflected and transmitted components are more diffuse.

In my view, confusion stems from the fact that there is so relatively little absorption within transparent materials that, when considering just the initial incidence of light on the surface, there is effectively only reflection and transmission. Thus, the fact that Fresnel equations do not consider absorption is absolutely right as they deal only with surface incidence. However, the reflectance of a transparent material also includes internal reflective effects from the rear boundary. As shown in the Reflectivity and Reflectance topic, these are not inconsiderable and this is where the absorption values of different glasses makes a real difference. When calculating the total reflectance, the Fresnel equations have to be applied multiple times as the light bounces back and forth between the front and rear faces. Each time, the incidence light value is degraded by absorption, thus affecting both overall reflectance and transmittance.

Units and Measures

Absorptance is measured as the ratio of the total amount of light or electromagnetic radiation that is absorbed compared to the total amount originally incident upon it. As such, it is a dimensionless fractional value between 0 and 1. Whilst a vacuum is the closest we can ever come to a material with an absorptance of 0, no real material other than perhaps a cosmic black hole has an absorptance of 1.

In some fields, the theoretical concept of a black body is used as a reference point for maximum absorbtance. This is defined as an idealised body that absorbs all radiation that falls on its surface, effectively having an absorptance of 1. Again, such a material does not exist, but it is possible to get reasonably close using a hole within a surface behind which is a cavity completely lined with black absorbing material.

Absorptivity

Absorptivity and absorbance are quite different. Absorptivity measures the attenuation of light radiant power with distance and is more commonly termed an attenuation coefficient. This is sometimes also termed an extinction coefficient, however it is important to note that extinction is a measure of both absorption and scattering. Absorptivity and attenuation coefficients are all given as fractional values per meter of distance travelled.

It is also very important that absorptance and is not confused in any way with absorbance which, like absorptivity, measures the attenuation of radiant power with distance but is a logarithmic ratio.

Example Values

The following are some calculated values of opaque surface aborptance for a range of common colours. Again, I used to have web references for these values but they have long since moved on or died, so you should treat these values as indicative.

COLOR NAME COLOR HEX ABS
AliceBlue #f0f8ff 0.081
AntiqueWhite #faebd7 0.132
AntiqueWhite1 #ffefdb 0.118
AntiqueWhite2 #eedfcc 0.174
AntiqueWhite3 #cdc0b0 0.281
AntiqueWhite4 #8b8378 0.495
aquamarine1 #7fffd4 0.114
aquamarine2 #76eec6 0.169
aquamarine4 #458b74 0.495
azure1 #f0ffff 0.062
azure2 #e0eeee 0.121
azure3 #c1cdcd 0.235
azure4 #838b8b 0.464
beige #f5f5dc 0.104
bisque1 #ffe4c4 0.159
bisque2 #eed5b7 0.211
bisque3 #cdb79e 0.314
bisque4 #8b7d6b 0.518
black #000000 0.943
BlanchedAlmond #ffebcd 0.135
blue1 #0000ff 0.827
blue2 #0000ee 0.835
blue4 #00008b 0.881
BlueViolet #8a2be2 0.684
brown #a52a2a 0.768
brown1 #ff4040 0.672
brown2 #ee3b3b 0.693
brown3 #cd3333 0.728
brown4 #8b2323 0.798
burlywood #deb887 0.317
burlywood1 #ffd39b 0.225
burlywood2 #eec591 0.272
burlywood3 #cdaa7d 0.368
burlywood4 #8b7355 0.556
CadetBlue #5f9ea0 0.412
CadetBlue1 #98f5ff 0.114
CadetBlue2 #8ee5ee 0.168
CadetBlue3 #7ac5cd 0.277
CadetBlue4 #53868b 0.491
chartreuse1 #7fff00 0.216
chartreuse2 #76ee00 0.265
chartreuse3 #66cd00 0.359
chartreuse4 #458b00 0.549
chocolate #d2691e 0.589
chocolate1 #ff7f24 0.513
chocolate2 #ee7621 0.544
chocolate3 #cd661d 0.599
coral #ff7f50 0.492
coral1 #ff7256 0.525
coral2 #ee6a50 0.555
coral3 #cd5b45 0.610
coral4 #8b3e2f 0.718
CornflowerBlue #6495ed 0.399
cornsilk1 #fff8dc 0.093
cornsilk2 #eee8cd 0.148
cornsilk3 #cdc8b1 0.258
cornsilk4 #8b8878 0.481
cyan1 #00ffff 0.129
cyan2 #00eeee 0.184
cyan3 #00cdcd 0.289
cyan4 #008b8b 0.501
DarkGoldenrod #b8860b 0.525
DarkGoldenrod1 #ffb90f 0.364
DarkGoldenrod2 #eead0e 0.402
DarkGoldenrod3 #cd950c 0.478
DarkGoldenrod4 #8b6508 0.630
DarkGreen #6400 0.676
DarkKhaki #bdb76b 0.345
DarkOliveGreen #556b2f 0.610
DarkOliveGreen1 #caff70 0.142
DarkOliveGreen2 #bcee68 0.196
DarkOliveGreen3 #a2cd5a 0.300
DarkOliveGreen4 #6e8b3d 0.509
DarkOrange #ff8c00 0.494
DarkOrange1 #ff7f00 0.530
DarkOrange2 #ee7600 0.559
DarkOrange3 #cd6600 0.612
DarkOrange4 #8b4500 0.721
DarkOrchid #9932cc 0.671
DarkOrchid1 #bf3eff 0.603
DarkOrchid2 #b23aee 0.626
DarkOrchid3 #9a32cd 0.670
DarkOrchid4 #68228b 0.759
DarkSalmon #e9967a 0.416
DarkSeaGreen #8fbc8f 0.325
DarkSeaGreen1 #c1ffc1 0.104
DarkSeaGreen2 #b4eeb4 0.160
DarkSeaGreen3 #9bcd9b 0.269
DarkSeaGreen4 #698b69 0.490
DarkSlateBlue #483d8b 0.694
DarkSlateGray #2f4f4f 0.683
DarkSlateGray1 #97ffff 0.087
DarkSlateGray2 #8deeee 0.144
DarkSlateGray3 #79cdcd 0.255
DarkSlateGray4 #528b8b 0.478
DarkTurquoise #00ced1 0.285
DarkViolet #9400d3 0.806
DeepPink1 #ff1493 0.751
DeepPink2 #ee1289 0.766
DeepPink3 #cd1076 0.792
DeepPink4 #8b0a50 0.845
DeepSkyBlue1 #00bfff 0.304
DeepSkyBlue2 #00b2ee 0.348
DeepSkyBlue3 #009acd 0.429
DeepSkyBlue4 #00688b 0.597
DimGray #696969 0.583
DodgerBlue1 #1e90ff 0.424
DodgerBlue2 #1c86ee 0.460
DodgerBlue3 #1874cd 0.526
DodgerBlue4 #104e8b 0.663
firebrick #b22222 0.790
firebrick1 #ff3030 0.723
firebrick2 #ee2c2c 0.741
firebrick3 #cd2626 0.770
firebrick4 #8b1a1a 0.827
FloralWhite #fffaf0 0.078
ForestGreen #228b22 0.543
gainsboro #dcdcdc 0.179
GhostWhite #f8f8ff 0.078
gold1 #ffd700 0.289
gold2 #eec900 0.332
gold3 #cdad00 0.418
gold4 #8b7500 0.590
goldenrod #daa520 0.421
goldenrod1 #ffc125 0.332
goldenrod2 #eeb422 0.374
goldenrod3 #cd9b1d 0.454
goldenrod4 #8b6914 0.613
gray #bebebe 0.284
gray1 #030303 0.939
gray2 #050505 0.932
gray3 #080808 0.921
gray4 #0a0a0a 0.914
gray5 #0d0d0d 0.904
gray6 #0f0f0f 0.897
gray7 #121212 0.886
gray8 #141414 0.879
gray9 #171717 0.869
gray10 #1a1a1a 0.858
gray11 #1c1c1c 0.851
gray12 #1f1f1f 0.841
gray13 #212121 0.834
gray14 #242424 0.824
gray15 #262626 0.817
gray16 #292929 0.806
gray17 #2b2b2b 0.799
gray18 #2e2e2e 0.789
gray19 #303030 0.782
gray20 #333333 0.771
gray21 #363636 0.761
gray22 #383838 0.754
gray23 #3b3b3b 0.743
gray24 #3d3d3d 0.736
gray25 #404040 0.726
gray26 #424242 0.719
gray27 #454545 0.709
gray28 #474747 0.702
gray29 #4a4a4a 0.691
gray30 #4d4d4d 0.681
gray31 #4f4f4f 0.674
gray32 #525252 0.663
gray33 #545454 0.656
gray34 #575757 0.646
gray35 #595959 0.639
gray36 #5c5c5c 0.628
gray37 #5e5e5e 0.621
gray38 #616161 0.611
gray39 #636363 0.604
gray40 #666666 0.594
gray41 #696969 0.583
gray42 #6b6b6b 0.576
gray43 #6e6e6e 0.566
gray44 #707070 0.559
gray45 #737373 0.548
gray46 #757575 0.541
gray47 #787878 0.531
gray48 #7a7a7a 0.524
gray49 #7d7d7d 0.513
gray50 #7f7f7f 0.506
gray51 #828282 0.493
gray52 #858585 0.483
gray53 #878787 0.476
gray54 #8a8a8a 0.465
gray55 #8c8c8c 0.458
gray56 #8f8f8f 0.448
gray57 #919191 0.441
gray58 #949494 0.430
gray59 #969696 0.423
gray60 #999999 0.413
gray61 #9c9c9c 0.402
gray62 #9e9e9e 0.395
gray63 #a1a1a1 0.385
gray64 #a3a3a3 0.378
gray65 #a6a6a6 0.368
gray66 #a8a8a8 0.361
gray67 #ababab 0.350
gray68 #adadad 0.343
gray69 #b0b0b0 0.333
gray70 #b3b3b3 0.322
gray71 #b5b5b5 0.315
gray72 #b8b8b8 0.305
gray73 #bababa 0.298
gray74 #bdbdbd 0.287
gray75 #bfbfbf 0.280
gray76 #c2c2c2 0.270
gray77 #c4c4c4 0.263
gray78 #c7c7c7 0.253
gray79 #c9c9c9 0.246
gray80 #cccccc 0.235
gray81 #cfcfcf 0.225
gray82 #d1d1d1 0.218
gray83 #d4d4d4 0.207
gray84 #d6d6d6 0.200
gray85 #d9d9d9 0.190
gray86 #dbdbdb 0.183
gray87 #dedede 0.172
gray88 #e0e0e0 0.165
gray89 #e3e3e3 0.155
gray90 #e5e5e5 0.148
gray91 #e8e8e8 0.138
gray92 #ebebeb 0.127
gray93 #ededed 0.120
gray94 #f0f0f0 0.110
gray95 #f2f2f2 0.103
gray97 #f7f7f7 0.085
gray98 #fafafa 0.075
gray99 #fcfcfc 0.068
green1 #00ff00 0.251
green2 #00ee00 0.298
green3 #00cd00 0.388
green4 #008b00 0.569
GreenYellow #adff2f 0.181
honeydew1 #f0fff0 0.069
honeydew2 #e0eee0 0.127
honeydew3 #c1cdc1 0.241
honeydew4 #838b83 0.468
HotPink #ff69b4 0.503
HotPink1 #ff6eb4 0.489
HotPink2 #ee6aa7 0.511
HotPink3 #cd6090 0.559
HotPink4 #8b3a62 0.705
IndianRed #cd5c5c 0.597
IndianRed1 #ff6a6a 0.538
IndianRed2 #ee6363 0.565
IndianRed3 #cd5555 0.619
IndianRed4 #8b3a3a 0.724
ivory1 #fffff0 0.064
ivory2 #eeeee0 0.123
ivory3 #cdcdc1 0.237
ivory4 #8b8b83 0.465
khaki #f0e68c 0.184
khaki1 #fff68f 0.134
khaki2 #eee685 0.188
khaki3 #cdc673 0.296
khaki4 #8b864e 0.507
lavender #e6e6fa 0.135
LavenderBlush1 #fff0f5 0.103
LavenderBlush2 #eee0e5 0.159
LavenderBlush3 #cdc1c5 0.268
LavenderBlush4 #8b8386 0.486
LawnGreen #7cfc00 0.225
LemonChiffon1 #fffacd 0.094
LemonChiffon2 #eee9bf 0.152
LemonChiffon3 #cdc9a5 0.261
LemonChiffon4 #8b8970 0.482
light #eedd82 0.214
LightBlue #add8e6 0.199
LightBlue1 #bfefff 0.119
LightBlue2 #b2dfee 0.175
LightBlue3 #9ac0cd 0.282
LightBlue4 #68838b 0.493
LightCoral #f08080 0.468
LightCyan1 #e0ffff 0.066
LightCyan2 #d1eeee 0.125
LightCyan3 #b4cdcd 0.239
LightCyan4 #7a8b8b 0.466
LightGoldenrod1 #ffec8b 0.164
LightGoldenrod2 #eedc82 0.216
LightGoldenrod3 #cdbe70 0.319
LightGoldenrod4 #8b814c 0.521
LightGoldenrodYellow #fafad2 0.094
LightGray #d3d3d3 0.211
LightPink #ffb6c1 0.286
LightPink1 #ffaeb9 0.312
LightPink2 #eea2ad 0.355
LightPink3 #cd8c95 0.436
LightPink4 #8b5f65 0.603
LightSalmon1 #ffa07a 0.382
LightSalmon2 #ee9572 0.421
LightSalmon3 #cd8162 0.492
LightSalmon4 #8b5742 0.641
LightSeaGreen #20b2aa 0.371
LightSkyBlue #87cefa 0.227
LightSkyBlue1 #b0e2ff 0.159
LightSkyBlue2 #a4d3ee 0.211
LightSkyBlue3 #8db6cd 0.313
LightSkyBlue4 #607b8b 0.518
LightSlateBlue #8470ff 0.483
LightSlateGray #778899 0.469
LightSteelBlue #b0c4de 0.256
LightSteelBlue1 #cae1ff 0.154
LightSteelBlue2 #bcd2ee 0.207
LightSteelBlue3 #a2b5cd 0.309
LightSteelBlue4 #6e7b8b 0.514
LightYellow1 #ffffe0 0.072
LightYellow2 #eeeed1 0.130
LightYellow3 #cdcdb4 0.243
LightYellow4 #8b8b7a 0.472
LimeGreen #32cd32 0.351
linen #faf0e6 0.112
magenta #ff00ff 0.755
magenta2 #ee00ee 0.768
magenta3 #cd00cd 0.792
magenta4 #8b008b 0.842
maroon #b03060 0.723
maroon1 #ff34b3 0.648
maroon2 #ee30a7 0.670
maroon3 #cd2990 0.709
maroon4 #8b1c62 0.787
medium #66cdaa 0.277
MediumAquamarine #66cdaa 0.277
MediumBlue #0000cd 0.850
MediumOrchid #ba55d3 0.563
MediumOrchid1 #e066ff 0.485
MediumOrchid2 #d15fee 0.516
MediumOrchid3 #b452cd 0.575
MediumOrchid4 #7a378b 0.696
MediumPurple #9370db 0.496
MediumPurple1 #ab82ff 0.423
MediumPurple2 #9f79ee 0.459
MediumPurple3 #8968cd 0.527
MediumPurple4 #5d478b 0.661
MediumSeaGreen #3cb371 0.389
MediumSlateBlue #7b68ee 0.516
MediumSpringGreen #00fa9a 0.190
MediumTurquoise #48d1cc 0.259
MediumVioletRed #c71585 0.770
MidnightBlue #191970 0.821
MintCream #f5fffa 0.063
MistyRose1 #ffe4e1 0.145
MistyRose2 #eed5d2 0.198
MistyRose3 #cdb7b5 0.303
MistyRose4 #8b7d7b 0.510
moccasin #ffe4b5 0.166
NavajoWhite1 #ffdead 0.186
NavajoWhite2 #eecfa1 0.237
NavajoWhite3 #cdb38b 0.334
NavajoWhite4 #8b795e 0.535
NavyBlue #80 0.886
OldLace #fdf5e6 0.097
OliveDrab #6b8e23 0.514
OliveDrab1 #c0ff3e 0.168
OliveDrab2 #b3ee3a 0.220
OliveDrab4 #698b22 0.523
orange1 #ffa500 0.426
orange2 #ee9a00 0.461
orange3 #cd8500 0.527
orange4 #8b5a00 0.664
OrangeRed1 #ff4500 0.689
OrangeRed2 #ee4000 0.707
OrangeRed3 #cd3700 0.741
OrangeRed4 #8b2500 0.809
orchid #da70d6 0.478
orchid1 #ff83fa 0.399
orchid2 #ee7ae9 0.436
orchid3 #cd69c9 0.507
orchid4 #8b4789 0.649
pale #db7093 0.509
PaleGoldenrod #eee8aa 0.165
PaleGreen #98fb98 0.146
PaleGreen1 #9aff9a 0.133
PaleGreen2 #90ee90 0.187
PaleGreen3 #7ccd7c 0.295
PaleGreen4 #548b54 0.506
PaleTurquoise #afeeee 0.134
PaleTurquoise1 #bbffff 0.077
PaleTurquoise2 #aeeeee 0.135
PaleTurquoise3 #96cdcd 0.247
PaleTurquoise4 #668b8b 0.472
PaleVioletRed #db7093 0.509
PaleVioletRed1 #ff82ab 0.439
PaleVioletRed2 #ee799f 0.474
PaleVioletRed3 #cd6889 0.540
PaleVioletRed4 #8b475d 0.672
PapayaWhip #ffefd5 0.121
PeachPuff1 #ffdab9 0.191
PeachPuff2 #eecbad 0.243
PeachPuff3 #cdaf95 0.340
PeachPuff4 #8b7765 0.537
pink #ffc0cb 0.254
pink1 #ffb5c5 0.287
pink2 #eea9b8 0.331
pink3 #cd919e 0.418
pink4 #8b636c 0.589
plum #dda0dd 0.343
plum1 #ffbbff 0.243
plum2 #eeaeee 0.292
plum3 #cd96cd 0.382
plum4 #8b668b 0.563
PowderBlue #b0e0e6 0.176
purple #a020f0 0.701
rebeccapurple #663399 0.706
purple1 #9b30ff 0.652
purple2 #912cee 0.674
purple3 #7d26cd 0.711
purple4 #551a8b 0.786
red1 #ff0000 0.877
red2 #ee0000 0.882
red3 #cd0000 0.891
red4 #8b0000 0.910
RosyBrown #bc8f8f 0.435
RosyBrown1 #ffc1c1 0.256
RosyBrown2 #eeb4b4 0.302
RosyBrown3 #cd9b9b 0.392
RosyBrown4 #8b6969 0.574
RoyalBlue #41690 0.817
RoyalBlue1 #4876ff 0.484
RoyalBlue2 #436eee 0.515
RoyalBlue3 #3a5fcd 0.574
RoyalBlue4 #27408b 0.695
SaddleBrown #8b4513 0.712
salmon #fa8072 0.475
salmon1 #ff8c69 0.445
salmon2 #ee8262 0.480
salmon3 #cd7054 0.546
salmon4 #8b4c39 0.675
SandyBrown #f4a460 0.387
SeaGreen1 #54ff9f 0.151
SeaGreen2 #4eee94 0.204
SeaGreen3 #43cd80 0.307
SeaGreen4 #2e8b57 0.515
seashell1 #fff5ee 0.093
seashell2 #eee5de 0.149
seashell3 #cdc5bf 0.260
seashell4 #8b8682 0.479
sienna #a0522d 0.659
sienna1 #ff8247 0.488
sienna2 #ee7942 0.520
sienna3 #cd6839 0.580
sienna4 #8b4726 0.698
SkyBlue #87ceeb 0.235
SkyBlue1 #87ceff 0.225
SkyBlue2 #7ec0ee 0.274
SkyBlue3 #6ca6cd 0.366
SkyBlue4 #4a708b 0.554
SlateBlue #6a5acd 0.574
SlateBlue1 #836fff 0.486
SlateBlue2 #7a67ee 0.519
SlateBlue3 #6959cd 0.577
SlateBlue4 #473c8b 0.697
SlateGray #708090 0.497
SlateGray1 #c6e2ff 0.153
SlateGray2 #b9d3ee 0.205
SlateGray3 #9fb6cd 0.307
SlateGray4 #6c7b8b 0.514
snow1 #fffafa 0.073
snow2 #eee9e9 0.133
snow3 #cdc9c9 0.244
snow4 #8b8989 0.468
SpringGreen1 #00ff7f 0.192
SpringGreen2 #00ee76 0.243
SpringGreen3 #00cd66 0.340
SpringGreen4 #008b45 0.536
SteelBlue #4682b4 0.486
SteelBlue1 #63b8ff 0.295
SteelBlue2 #5cacee 0.338
SteelBlue3 #4f94cd 0.423
SteelBlue4 #36648b 0.592
tan #d2b48c 0.329
tan1 #ffa54f 0.389
tan2 #ee9a49 0.426
tan3 #cd853f 0.498
tan4 #8b5a2b 0.644
thistle #d8bfd8 0.262
thistle1 #ffe1ff 0.139
thistle2 #eed2ee 0.193
thistle3 #cdb5cd 0.297
thistle4 #8b7b8b 0.506
tomato1 #ff6347 0.573
tomato2 #ee5c42 0.599
tomato3 #cd4f39 0.649
tomato4 #8b3626 0.744
turquoise #40e0d0 0.218
turquoise1 #00f5ff 0.157
turquoise2 #00e5ee 0.208
turquoise3 #00c5cd 0.311
turquoise4 #00868b 0.514
violet #ee82ee 0.412
VioletRed #d02090 0.733
VioletRed1 #ff3e96 0.635
VioletRed2 #ee3a8c 0.655
VioletRed3 #cd3278 0.698
VioletRed4 #8b2252 0.778
wheat #f5deb3 0.186
wheat1 #ffe7ba 0.155
wheat2 #eed8ae 0.207
wheat3 #cdba96 0.309
wheat4 #8b7e66 0.518
white #ffffff 0.057
WhiteSmoke #f5f5f5 0.092
yellow1 #ffff00 0.180
yellow2 #eeee00 0.231
yellow3 #cdcd00 0.330
yellow4 #8b8b00 0.529
YellowGreen #9acd32 0.321

Table 1: Some example absorptances for opaque surfaces with common colours.

Useful References


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