The Col o r of Light – Notes

inverselyThe wavelength and frequency of EM waves are inversely proportional (c = f). Seven types of electromagnetic radiation. Electromagnetic Spectrum EM Spectrum

Electromagnetic Spectrum EM Spectrum

Electromagnetic Spectrum Seven types: Radio Waves – cannot be heard, but can carry sound waves Microwaves - cause food molecules to vibrate and cook itself Infrared – heat waves Visible Light – only electromagnetic wave we can see Ultraviolet – causes sunburns X-rays – caused by high speed electrons crashing into metal plates Gamma Rays – accompany most nuclear reactions (lowest frequency  highest frequency) (lowest energy  highest energy) (longest wavelength  shortest wavelength)

Electromagnetic Spectrum Visible light is the part of the electromagnetic spectrum humans can see Ranges from wavelengths of 400 nm to 700 nm. FYI: 1 nm = m

The colors we see depend upon the frequency of light (wavelength) we see. The lowest frequency we can detect appears red to most people. The highest frequency we detect appears violet to most people. In between these two is a wide range of frequencies and an infinite number of hues that make up the color spectrum of the rainbow.

ROYGBIV By convention, these colors are grouped into seven colors: Red674 nm Orange616 nm Yellow580 nm Green556 nm Blue458 nm Indigo410 nm Violet400 nm Rainbow

White Light The white light from the sun is a combination of ALL the visible frequencies. White light is made of COLORED LIGHT! This can be demonstrated by passing sunlight through a prism and observing the rainbow colored spectrum. White Light

What determines what color we see? a.It depends on what color the object reflects. b.It depends on what color the object absorbs. c.It depends on the type of object as it could either be what color is reflected or absorbed.

Opaque Objects: The color of opaque objects is determined by 2 things: 1. The color of light reflected by the object. Most objects are illuminated with white light. In that case: –A–An opaque object that reflects all of the light that hits it appears white. –A–An opaque object that absorbs all the light that hits it appears black. –A–An object that absorbs all the wavelengths except green – appears green because it reflects the green wavelength of light.

2. The kind of light used. An object can only reflect frequencies that are present in the illuminating light. This is why some objects appear slightly different colors in different types of light (candle light vs. incandescent vs. fluorescent). If you shine red light on a rose, the petals will appear red, while the stems and leaves will appear black. Do you see why?

Transparent Objects: The color of transparent objects depends on the color of light they transmit. A blue piece of glass appears blue because it absorbs all the colors of white light that hit it except blue –which it transmits. Just like other objects, the glass contains dyes or pigments, which selectively absorb certain colors of light and transmit others.

Colored Understanding Black objects _______ all of the pure colors. White objects _______ all of the pure colors. Transparent objects _______ all of the pure colors. absorb reflect transmit

MIXING COLORED LIGHT First: Forget all you learned about mixing paints in 1st grade and in art for that matter. Those are pigments and we’re talking light here! We have seen that all the visible frequencies of light mixed together produce white. The distribution of solar frequencies is not equal, however. The most intense portion of the spectrum is the yellow-green area. This can be seen in the radiation curve below.

MIXING COLORED LIGHT Interestingly enough, the perception of white also results from the combination of only red, green and blue light. This can be explained by simplifying the radiation curve to look like this.

Overlapping red, green and blue light shows how these colors ADD to produce white light. If only two of the colors overlap, a new color will be seen. By adding various amounts of red, green and blue light together we can produce any color in the spectrum. Copywrited by Holt, Rinehart, & Winston

Primary COLORS of LIGHT Red, green and blue Called the additive colors. Primary Colors Copywrited by Holt, Rinehart, & Winston

Mixing Colors Mixing these additive primary colors produces: Secondary colors of light (additive secondary colors) Primary Colors  Secondary Light Colors Red + green = yellow Red + blue = magenta (purple) Green + blue = cyan (turquoise)

Note that cyan is the addition of green and blue. Note that yellow is the addition of red and green. White Red Green Blue Yellow Cyan Magenta Colors in White Light Note that magenta is the addition of red and blue. You can see that these three add to give white.

MIXING COLORED PIGMENTS

Finger Painting Flashback Everyone knows that if you mix red, green, and blue paint – you don’t get white! You get a muddy dark brown! Mixing pigments/dyes is an entirely different process than mixing light! Let’s relate pigments and reflected light to what we see! To do this we use color tiles.

Color Tiles Rules for color tiles: Each of the three primary additive colors of light are considered separately. When mixing pigments, if either pigment absorbs a light color, that light color is not reflected. Draw these diagrams as we work through these problems together.

RED PIGMENT : (illuminated by white light) The red wavelengths are reflected while the green and blue wavelengths are absorbed. WE SEE RED! In black and white drawing, we indicate absorption by shading in the box.

GREEN PIGMENT : (illuminated by white light) The green wavelengths are reflected, while the red and blue wavelengths are absorbed. WE SEE GREEN!

RED and GREEN PIGMENT MIXED Here the red incident light would be reflected if only red pigment were present, but instead it is absorbed due to the presence of the green pigment. The green light is absorbed due to the red pigment, and the blue light is absorbed by both. No light is reflected so WE SEE BLACK!!!!

Review Primary Light ColorsSecondary Light Colors Red + green light = _______ light Red + blue light = _______ light Green + blue light = _______ light yellow magenta cyan

But what if we mixed cyan pigment and yellow pigment? Remember, cyan pigment appears cyan in color because blue and green light is reflected from the pigment and ADD together to appear cyan.

Red Wavelengths: Since cyan light is made of green and blue light, those two colors are reflected, but the red portion of incident light is absorbed by cyan.

Green Wavelengths: Cyan will reflect green wavelengths but we must also consider the yellow pigment. The color yellow is seen because red and green light reflects and adds together. Yellow DOES reflect green. Both pigments individually reflect green light. Therefore green light will also be reflected by a mixture of the two pigments. We will see GREEN !

Blue Wavelengths: Cyan pigment reflects blue light, but what about yellow pigment? Yellow pigment reflects red and green – BUT NOT BLUE! So even though alone cyan could reflect blue, the mixture will absorb it because yellow pigment is present.

Try mixing magenta and yellow pigment. We see RED!

Cyan pigment + magenta pigment We see BLUE!

Primary Color of Pigments Magenta, cyan and yellow are the PRIMARY COLORS OF PIGMENTS. You probably learned these as Red (magenta) Blue (cyan) and yellow. Unlike with light, combining pigments is a SUBTRACTIVE process. The more pigments you combine, the less light you see (because more gets absorbed!)

Summing up Color Mixing: Combinations of red, green, and blue light produce cyan, magenta and yellow light. Mixing magenta, cyan, and yellow pigments allows red, blue and green light to be reflected (and seen).

Color Chart Primary ColorsSecondary Colors LightRedCyan GreenMagenta BlueYellow PigmentCyanRed MagentaGreen YellowBlue

Secondary & Complimentary Colors Red + green=yellow Red + blue=magenta Blue + green=cyan A color plus its opposite appear white. We call any two colors that add together to produce white COMPLIMENTARY COLORS. magenta is opposite green: cyan is opposite red; and yellow is opposite blue.

Subtractive Colors Subtracting Color Subtractive Color

Color Printing Color Printing