2Introduction Color. Or is it? How beautiful the world is because of color!So easy to understand.It’s one of the first concepts children learn.It’s real.It’s universal.Or is it?It’s not simple.It’s not real.It’s not universal.
4But why should a color wheel work? The spectrum is linear! 575 nm400 nm450 nm520 nm700 nmNewton’s “color wheel”
5Color wheels for mixing paint to neutralize color: OK. yellowgreenredcyanNot OK for assigning visual complement inspectroscopic analysis of compounds !!magentablue
6cosmic gamma X-rays UV Vis IR Radio induction power Color is our brain’s response to light.“Light” is a term that refers to a electromagnetic radiation.And electromagnetic radiation are waves of different energies that extend over a broad range:frequency, Hz Hzcosmic gamma X-rays UV Vis IR Radio induction powerwavelength, nm nmIf the electromagnetic spectrum were a piano keyboard…..the visible spectral region would be just one key!
7Each of the “colors” of visible light has a corresponding wavelength between 400 to 700 nanometers (or nm).565 nmLight having a wavelength of near 565 nm will look yellow to most people.500600700750650550450400Is this because the eye has a specific detector (or receptor) for 565 nm yellow light?And a different receptor for 450 nm blue light? And another one for 650 red-orange light?And so on, for every wavelength between 400 and 700 nm?Seems like that would be a LOT of different types of receptors.Nature is “smarter” —and more efficient—than that.Only three different receptors for visible light are used.
8Beauty in the eye of the beholder.1 Your eyes have only three color receptors (detectors)- the RGB cones (red-green-blue)It is the brain that interprets visible light as “having” color.
9Beauty in the eye of the beholder.2 Yellow light is perceived by our eyes when two color receptors, Red and Green,are stimulated simultaneously.This is indicated on the diagram by the red and green arrows.It is the brain that interprets yellow light as “having” a yellow color.
10stimulate the Red and Green receptors. See?” Beauty in the eye of the beholder.3“What about red-orange?”, you say. “Red-orange light would also simultaneouslystimulate the Red and Green receptors. See?”Aaahhh…..true. But look! The relative lengths of the arrows are different.The green arrow, i.e. G-receptor, is much less stimulated than the R -receptor.So, red-orange light is seen as different from yellow light due tothe ratio of R and G response.
11It is the brain that interprets color. Beauty in the eye of the beholder.4When the R receptor gets about the same signal as the G receptor, or R = G,yellow is perceived.When the R receptor gets a larger response the the G receptor,something like R = 3G, red-orange is perceived.It is the brain that interprets color.
15Maxwell’s Triangle This triangle was devised to illustrate how three primary colors —Red, Green,Blue—can be added together to generate the othercolors.At the center of the triangle is white.The colors in the triangle can assignedthree coordinates, like a vector,determined by how much redor blue or greenis mixed to make that color.For example,a saturated red added toa saturated green makes …yellow.Red and green make YELLOW???Yup.We’ll show you how.
16Maxwell’s Triangle Think of the saturated red and green colors on Maxwell’s diagram as vectors.Now, imagine “decomposing” these R and Gvectors into the sum of the dashed arrows.
17Maxwell’s Triangle See how two of the decomposed vectors that run along the right edge of the triangleare co-linear but point in exactly opposite directions?They cancel each other.This leaves the shorter vectors componentsthese vectors have the same direction andpoint from yellow.They represent the yellow “product”from adding red and green.
18Maxwell’s TriangleBlue + Yellow = White?!Blue + yellow vectorspoint in exactly oppositedirection and cancel tomake white.
27blue + yellow = green One light beam!!!! Subtractive color mixing: light colors are subtracted from one white light beamblue + yellow = greenwhite light beam =sum of all spectral colorsreflectsthis muchspectrumlightreflectedBy bothblue paintshining on:reflectsGreenis only color reflected by both the blue and yellow paints.All red, orange, yellow, blue, violet removed.yellow paintOne light beam!!!!
28A transmittance —or reflectance— spectrum reflects this much spectrum ultramarinelight reflected by bothreflectschrome yellow
29blue + yellow = green One light beam!!!! white light beam = sum of all spectral colorsThis blue reflects no violet.lightreflectedby bothblue paint(cerulean)shining on:reflectsa brighter green, less dull, because the (violet + orange = brown) is absentyellow paint(lemon yellow)This yellow reflects no orange.One light beam!!!!
30reflects this much spectrum Cerulean blue reflects lemon yellow light reflected by bothreflectslemon yellow
31Light “hues” removed from one beam So the primary colors are not Red-Yellow-Blue??!!Primary Colors for Color MixingAdditiveMultiple light beams addedSubtractiveLight “hues” removed from one beamprimary colorsY-M-Cyellow/magenta/cyanY + M + C = Blackprimary colorsR-G-Bred-blue-greenR + G + B = Whitesecondary colorsY-M-Csecondary colorsR-B-GDemonstrate this:with 3 slide projectorsDemonstrate this:with transparencies
32(some) Color Terminology common ideascientific termHue green Lmax, nm or Dowhat color is grass?Saturation how intense the color, e, absorption coefficientrelative to greyLuminosity relative brightness concentration(Value) how much white/black is added (e.g., molarity)Non-spectral hues are not in the rainbow! are not a component of white lightexamples: are not due to one wavelength of lightbrown, salmon, magenta, purple, pink
34How does all this relate to spectroscopy of transition metals complexes?
35Conversion between the two primary color systems, Red-Green-Blue and Cyan-Magenta-Yellowillustrates the mathematical concept of equivalent basis setsand their interconversionExamples of changing 3-dimensional basis sets:Color space: RGB CMYGeometrical Space:Cartesian Coordinates (x,y,z,) into Spherical (Polar) Coordinates (r, )Chemical “Space”: Atomic orbitals and molecular orbitals