Color Addition Color Addition Light Waves and Color - Lesson 2 - Color and Vision Color Addition Blue Skies and Red Sunsets Color perception, like sound perception , is a complex subject involving the disciplines of psychology, physiology, biology, chemistry and physics. When you look at an object and perceive a distinct color, you are not necessarily seeing a single frequency of light. Consider for instance that you are looking at a shirt and it appears purple to your eye. In such an instance, there may be several frequencies of light striking your eye with varying degrees of intensity. Yet your eye-brain system interprets the frequencies that strike your eye and the shirt is decoded by your brain as being purple. Primary Colors of Light The subject of color perception can be simplified if we think in terms of primary colors of light. We have already learned that white is not a color at all , but rather the presence of all the frequencies of visible light. When we speak of white light, we are referring to ROYGBIV - the presence of the entire spectrum of visible light. But combining the range of frequencies in the visible light spectrum is not the only means of producing white light.

White light can also be produced by combining only three distinct frequencies of light, provided that they are widely separated on the visible light spectrum. Any three colors (or frequencies) of light that produce white light when combined with the correct intensity are called primary colors of light. There are a variety of sets of primary colors. The most common set of primary colors is red (R), green (G) and blue (B). When red, green and blue light are mixed or added together with the proper intensity, white (W) light is obtained. This is often represented by the equation below: R + G + B = W In fact, the mixing together (or addition) of two or three of these three primary colors of light with varying degrees of intensity can produce a wide range of other colors. For this reason, many television sets and computer monitors produce the range of colors on the monitor by the use of red, green and blue light-emitting phosphors. The addition of the primary colors of light can be demonstrated using a light box. The light box illuminates a screen with the three primary colors - red (R), green (G) and blue (B). The lights are often the shape of circles.

The result of adding two primary colors of light is easily seen by viewing the overlap of the two or more circles of primary light. The different combinations of colors produced by red, green and blue are shown in the graphic below. (CAUTION: Because of the way that different monitors and different web browsers render the colors on the computer monitor, there may be slight variations from the intended colors.) Color Addition Rules These demonstrations with the color box illustrate that red light and green light add together to produce yellow (Y) light. Red light and blue light add together to produce magenta (M) light. Green light and blue light add together to produce cyan (C) light. And finally, red light and green light and blue light add together to produce white light. This is sometimes demonstrated by the following color equations and graphic: R + G = Y Green and Magenta Blue and Yellow The production of various colors of light by the mixing of the three primary colors of light is known as color addition. The color addition principles discussed on this page can be used to make predictions of the colors that would result when different colored lights are mixed.

In the next part of Lesson 2 , we will learn how to use the principles of color addition to determine why different objects look specific colors when illuminated with various colors of light. We Would Like to Suggest ... Sometimes it isn't enough to just read about it. You have to interact with it! And that's exactly what you do when you use one of The Physics Classroom's Interactives. We would like to suggest that you combine the reading of this page with the use of our RGB Color Addition Interactive . The Interactive is found in the Physics Interactives section of our website and allows a learner to adjust the intensity of red, green, and blue spotlights shining upon a white surface and to observe the appearance. Explore the result of mixing R, G, and B lights in equal and unequal intensities. colors Colored Light versus Colored Pigments The science of color is a fascinating study. This essay will explore the physics of colored light and colored pigments, and the color physiology of the human eye. There are three primary colors of light: red, green and blue. Shining them at the same surface puts them together by addition, by adding them together.

Mixing the primary colors produces the intermediate or secondary colors, yellow, cyan and magenta as in the diagram below. Equal quantitites of red and green light together are perceived as yellow. Blue and green light together are perceived as cyan. Blue and red light together are perceived as magenta. All the other perceived colors and shades of color can be produced by blending specific amounts of the primary colors. Mixing equal amounts of red, green and blue yields white light. White light can also be produced by mixing the proper proportion of a color and its opposite. Red and cyan, green and megenta, or blue and yellow light shined on the same area will appear as white light. For this reason, opposite colors are called complementary colors. Note that this white light appears white, but does not contain all the colors of the spectrum like, for example, sunlight. Full-spectrum white light is a combination of all the colors of the rainbow. Shine complete white light on a prism or upon water droplets in the air and you will see a rainbow of all the colors. The opaque pigments work differently. Pigments absorb light. The light they reflect is the color we perceive.

Mixing pigments works by subtraction, by absorbing colors from the light that shines on them. When you have something printed at the print shop, the printer will usually mix magenta, yellow and cyan pigments to produce all the colors. Each color of pigment absorbs its opposite (complementary color) on the diagram below. Magenta pigment absorbs green light. Yellow pigment absorbs blue light. Cyan pigment absorbs red light. Transparent pigments work similarly, but instead of reflecting colors, they allow them to pass through. To make a pure red print color, blue and green have to be absorbed. Yellow absorbs blue and magenta absorbs green. So a mixture of yellow and magenta pigments will absorb all other colors and reflect red - thus creating the appearance of a red colored object. Similarly, mixing magenta (which absorbs green) and cyan (which absorbs red) yields a blue color. Mixing cyan (which absorbs red) and yellow (which absorbs blue) yields a green color. Mixing Colored Light MIXING LIGHTS AND PAINTS MIXING LIGHTS AND PAINTS Light comes in the colors of the spectrum (like the colors in a rainbow).

White light from the sun or an incandescent lamp (one that creates light from intense heat) contains all colors of the spectrum. A prism or a water drop breaks up a beam of white light into the spectrum. Paint can produce other colors as well, like brown, that do not exist in the spectrum. (This effect appears to depend on having color on a surface.) Mixing light adds up the lights: If you take two colored lights and mix them, the sum is lighter (more light) and the color is at least slightly less saturated (paler and closer to colorless or white light). For example, Red and Yellow add up to an Orange that has more light and is less saturated (more pastel) than the lights that went into it. Carefully chosen Yellow and Blue lights added together produce a neutral (colorless) light containing more light energy than the Yellow and Blue lights. Paint produces color from white light shining on it by absorbing (subtracting) many wavelengths (� colors) in the white light and reflecting only a few. The reflected light reaches your eye; the absorbed light is lost.

Green paint looks green under white light, because its pigments (colorings) reflect more of the green part of white light and absorb more of the other parts of white light. Blue paint looks blue under white light, because its pigments reflect more of the blue part of white light and absorb more of the other parts of white light. Because paint produces color by subtracting (absorbing) light from white light, each paint in a mixture subtracts some the light that the other paint normally reflects. Therefore, a mixture of paints reflects mostly those wavelengths that both paints in the mixture partially reflects. The total reflection from a paint mixture provides less light to the eye than does either paint alone. For example, mixing green and blue paints produces a blue-green that reflects less light than either of the paints alone. Mixing yellow and blue paint produces a green, because the paints together subtract less from the green part of white light than from any other part. Photopigments Light can be described in three ways. Each way is useful for different purposes. For the purpose of understanding how light is focused, it is often useful to describe light as rays traveling in straight lines. Light can also be described as waves, in which wavelength is related to color.

Finally light can be described as made up of packets of energy called photons, whose energy is related to color. For understanding photopigments, the photon description is most useful. At least one photon of light must be absorbed in the rods and cones to generate neural signals that the brain can read. This process of transduction depends on specific chemicals called photopigments: the single rod photopigment is called rhodopsin; the three cone photopigments are called iodopsins. Each is made of a large protein molecule that has attached to it a molecule of retinene, a chemical derived from Vitamin A. The protein molecules differ among the four photopigments (3 cone & 1 rod) to make the four absorb best photons of different energies (colors). The iodopsin in the "Red" cone absorbs best (photons that have energies equivalent to) 560 nm. The iodopsin in the "Green" cone absorbs best (photons that have energies equivalent to) 530 nm. The iodopsin in the "Blue" cone absorbs best (photons that have energies equivalent to) 420 nm.

Photons with (energies equivalent to) other wavelengths are less and less likely to be absorbed the further they are from the best energy (wavelength). When a photon is absorbed, it tears apart the photopigment molecule that absorbs it, releasing energy in the process. This energy through a series of steps ends up triggering a neural response in the cone. This is an example of transduction: light energy triggers neural signals. The neural response produced by breakup of photopigment molecules activates synaptic connections to bipolar cells, and the signal starts on its way towards the brain. The two pieces into which the iodopsin is broken, must be put back together before they can absorb another photon. Strong light breaks down photopigments faster than it can be put back together, decreasing the number of photopigment molecules in the rods and cones. Thus, there are fewer molecules of photopigment to absorb photons, and the eye is less sensitive to light. This is an important part of light adaptation. In the dark, the photopigments are not broken down any more, so the receptors fill up again as the previously broken down pieces get put back together. As this happens the eye becomes more and more sensitive to light.

This is an important part of dark adaptation. (Other parts of dark [and light] adaptation involve opening [closing] the pupil to admit more [less] light and changing average neural activity in retina.) Primary Colors of Light - Mixing of Colors - YouTube Primary Colors of Light - Mixing of Colors Want to watch this again later? Sign in to add this video to a playlist. Need to report the video? Sign in to report inappropriate content. Rating is available when the video has been rented. This feature is not available right now. Please try again later. Uploaded on May 13, 2011 When the primary colors of light, red, green, and blue are mixed, white light is produced. By looking at the shadows cast when an object blocks one or more of these color components, one can observe both the additive and subtractive processes of color mixing. Instead of subtracting light via an absorbing pigment, the object's shadow "removes" the component color from the "white" light. For example, the yellow shadow is the result of blocking the blue led and only allowing red and green to mix. Similarly, yellow pigment absorbs blue light and reflects red and green. The addition of red and green light makes yellow.

The bluish-green shadow - CYAN - is the result of blocking the red light. Where the cyan and yellow shadow overlaps appears to be green. Why? This small shadow is where both red and blue are blocked. Likewise, when we mix cyan and yellow pigment cyan absorbs red and yellow absorbs blue. The only thing left to be reflected is green. Cyan pigment and yellow pigment both reflect green, so that's what we see. (In white light) This is the bulb I used. Color Mixing with Red, Green, & Blue LEDs Color Mixing with Red, Green, & Blue LEDs Average (6-10 days) Prerequisites To do this project you should be familiar with Ohm's law. Experience building electronic circuits on a solderless breadboard is also helpful. The breadboard is the biggest expense, which can be used for future explorations in electronics. Material Availability Adult supervision required when using power drill. Abstract This is a good project for someone who is interested in both electronics and color vision. The equipment needed is on the expensive side, but if you continue studying electronics, you can use it again and again. Objective The goal of this project is to learn some basic principles of color perception by experimenting with various combinations of colored lights.

For controlled light sources, you will build an electronic circuit to control the current for three separate LEDs: one red, one green, and one blue. Credits Andrew Olson, Ph.D., Science Buddies Sources This project is based on: Calvert, J.B., 2002. "Electronics 45: Color," [accessed March 5, 2007] ~etuttle/electron/elect45.htm . Cite This Page MLA Style Science Buddies Staff. "Color Mixing with Red, Green, & Blue LEDs" Science Buddies. Science Buddies, 19 Aug. 2016. Web. 19 Dec. 2016 < APA Style Science Buddies Staff. (2016, August 19). Color Mixing with Red, Green, & Blue LEDs. Retrieved December 19, 2016 from Share your story with Science Buddies! I Did This Project! Please log in and let us know how things went. Last edit date: 2016-08-19 Introduction An LED (light-emitting diode) is a special kind of diode that produces light (see Figure 1). Figure 1.

A red LED (top). The longer lead is the anode (+) and the shorter lead is the cathode (−). In the schematic symbol for an LED (bottom), the anode is on the left and the cathode is on the right (Hewes, 2006). When current flows through the diode in the forward direction, some of the current is converted into light of a specific color (i.e., wavelength). The color of the light depends on the material from which the semiconductor is made. LEDs are available in many different colors. As the current through the LED increases, the brightness also increases. Typically, the recommended current for an LED is 20 mA or less. Above this value, the lifetime of the LED will be decreased significantly. Far above this value, the LED will fail catastrophically, like a flashbulb. To keep the LED current at a reasonable level, LEDs are typically connected in series with a current-limiting resistor, as shown in Figure 2. Figure 2. Schematic diagram of an LED in series with a 1kΩ resistor (Hewes, 2006).

The voltage drop across an LED is about 2 V (except for blue or white LEDs, where the voltage drop is about 4 V). In the circuit in Figure 2, the voltage drop across the resistor will be 9 − 2 = 7 V. Using Ohm's law, the current, I, through the resistor will be V/R = 7 V/1kΩ = 7 mA. Figure 3 shows you how to use Ohm's Law to calculate what size resistor you need to limit the current through the LED to the desired value. The voltage drop across the resistor will equal the supply voltage minus the voltage drop across the LED (or, VS − VL). You can then use Ohm's Law to calculate the resistance, R, needed to produce a desired current, I: R = (VS − VL)/I. So, if the supply voltage is +7 V, what resistor would you need for a 15 mA current? R = (7 − 2)/0.015 A = 333Ω. The closest standard resistor value would be 330 Ω.

For more details, and a set of online calculators, see the LED references in the Bibliography section (Hewes, 2006; Ngineering, 2003). Figure 3. Schematic diagram showing how to use Ohm's Law to calculate the correct value for the current-limiting resistor (Hewes, 2006). For this project, we'd like to vary the output of each of three different LEDs over a continuous range. Obviously, it would be a major inconvenience if we had to keep changing the current-limiting resistor for each LED! The circuit shown in Figure 4 is a different approach to solving our problem. Figure 4. This circuit uses an operational amplifier (op-amp) to control the current through an LED (Calvert, 2002). The large triangle marked "LF411" in the center of the schematic is an operational amplifier, or op-amp, for short. An op-amp has two inputs and one output.

(It also has positive and negative supply inputs, typically +/− 15 V, which are usually not shown in schematics.) In the schematic, the first input (marked +, and called the non-inverting input) is connected to a potentiometer. The second input (marked −, and called the inverting input) is connected to two circuit elements. It connects to the cathode of an LED, and to a 330 Ω resistor that connects to ground. The output of the op-amp is connected to the anode of that same LED. So the output of the op-amp is fed back to the inverting input, after first passing through the LED. Op-amps are almost always used with some type of feedback. What does the op-amp do? For a good basic understanding of how op-amps work in circuits, you just need to understand two simple rules (Horowitz and Hill, 1989, 177): "The output attempts to do whatever is necessary to make the voltage difference between the two inputs zero. "The inputs draw no current." These rules are simplifications—for example, the inputs do draw some current.

For the LF411 op-amp used in this project, 0.2 nA. You won't be able to measure that with your DMM! So these op-amp rules, as the authors state, are "good enough for almost everything you'll ever do," (Horowitz and Hill, 1989, 177). What do the op-amp rules mean for our LED control circuit? Let's examine the inputs to the op-amp to figure it out. The potentiometer connected to the non-inverting input provides a voltage, ranging between 0 and +5 V, depending on how far the knob is turned. Simple enough. OK, what about the inverting input? This is the feedback connection from the output. So, by rule 1, the op-amp output should do whatever is necessary to make the voltage at the inverting input match the voltage we set with the potentiometer. Let's consider three examples: with the potentiometer knob all the way down (0 V), half-way up (+2.5 V), and all the way up (+5 V). Example 1 is the easiest.

With 0 V at the non-inverting input, there should be 0 V at the inverting input (rule 1), so the op-amp does nothing. No current flows through the LED. With the potentiometer half-way up, the non-inverting input of the op-amp sees +2.5 V. How does the op-amp match that at the inverting input? It does it by passing current through the LED. How much current? Enough current so that the voltage at the inverting input equals +2.5 V. Where does the current go? The current flows to ground through the 330 Ω resistor (by rule 2, we know that the inputs draw no current, so the resistor is the only path to ground). By Ohm's Law, we have I = V/R = 2.5 V/330 Ω = 7.6 mA. So with the potentiometer half-way up, the op-amp output will provide 7.6 mA of current to the LED. With the potentiometer all the way up, there is now +5 V at the non-inverting input.

By the same analysis, we conclude that the current through the LED is now 15.2 mA. Perfect! The circuit has just the right range for a typical LED. The LF411 can supply 15 mA without a problem, so the behavior we expect from our op-amp rules is exactly the behavior that we get. You can see from Ohm's Law that the LED current increases in direct proportion to the voltage from the potentiometer. Do some more calculations for more potentiometer settings to convince yourself that this is true. Then build the circuit and see how it actually performs. You'll be able to control the LED with good precision and repeatability. What colors will you be able to produce from red, green, and blue? Terms and Concepts To do this project, you should do research that enables you to understand the following terms and concepts: Ohm's law Perception Questions If you wanted the output current through the LED to max out at about 10 mA, what resistor would you use in place of the 330 Ω resistor in the LED control schematic? The voltage drop across an LED is about 2 V for red and green, and about 4 V for blue.

What voltage would you expect to measure at the LF411 output (pin 6) when the potentiometer is half-way up (+2.5 V)? When the potentiometer is all the way up (+5 V)? What combination of intensities from red, green, and blue LEDs makes yellow light? Orange light? Purple light? Magenta light? White light? Bibliography You can read more about how we sense colors at these sites: Cooper, K. and C.J. Kazilek. (n.d.). Seeing Color. Ask a Biologist, Arizona State University. Retrieved March 5, 2007, from . Franklin Institute. (n.d.). Light and Color. Resources for Science Learning, The Franklin Institute. Retrieved March 5, 2007, from . You can practice mixing colors with light on your computer screen with this website: Oregon Museum of Science and Industry. (n.d.). Mixing Primary Colors. Retrieved April 28, 2015, from This webpage has useful information on LEDs: Hewes, J. (n.d.). Light Emitting Diodes (LEDs). The Electronics Club, Kelsey Park Sports College.

Retrieved April 23, 2014, from . Here is a page with an explanation of Ohm's Law: Physics Department Staff. (n.d.). Ohm's Law. Physics Department, University of Guelph. Retrieved March 8, 2007, from . The following references are recommended for more-advanced students: Science Buddies Staff. (n.d.). How to Use a Breadboard. Retrieved September 25, 2015, from More-advanced students will benefit from reading this page, which is the original source on which this project is based: Calvert, J.B. (2002). Electronics 45: Color. Retrieved March 5, 2007, from ~etuttle/electron/elect45.htm . If you want to learn more about how op-amps work, this book is an excellent reference source, and we recommend it highly to those who are seriously interested in learning more about electronics: Horowitz, P. and W. Hill (2015). The Art of Electronics, Third Edition. Cambridge, UK: Cambridge University Press. Here are some additional electronics books, recommended by Prof. James B.

Calvert, Associate Professor Emeritus of Engineering, University of Denver: A. S. Sedra, A.S., and K.C. Smith (1987). Microelectronic Circuits, Second Edition. New York, NY: Holt, Rinehart and Wilson. Jones, M.H. (1995). A Practical Introduction to Electronic Circuits, Third Edition. Cambridge, UK: Cambridge University Press. ARRL. (2006). The ARRL Handbook for Radio Communications. Newington, CT: American Radio Relay League. (Frequently updated with new editions. Title varies slightly; for example, older editions entitled The ARRL Handbook for the Radio Amateur. Newer edition preferred, but any would be suitable. Dr. Calvert remarks: "A good source of explanations, practical information and data, with emphasis on communications electronics.") Here is the technical data sheet for the LF411 op-amp (requires Adobe Acrobat Reader): National Semiconductor. (2004). LF411: Low Offset, Low Drift JFET Input Operational Amplifier. Jameco Electronics. Retrieved March 8, 2007, from .

News Feed on This Topic , , Note: A computerized matching algorithm suggests the above articles. It's not as smart as you are, and it may occasionally give humorous, ridiculous, or even annoying results! Learn more about the News Feed Materials and Equipment Heat shrink tubing, part #71871 Notes on electronics parts: The powered breadboard is expensive, but well worth it if you plan on doing more electronics experiments in the future. You could also check with a local university to see if you can get access to an electronics lab with a powered breadboard to do your project. The LF411CN IC is a static-sensitive part. Only three are used in the project, but six are specified so that you'll have spares in case of a mishap. One extra of each color LED is specified. You may prefer to use audio taper potentiometers instead, see the Variations section for a suitable Jameco part number. Tools: Empty tunafish can (washed; watch out for burrs) Small cardboard box One slab of paraffin wax (available at grocery store in 1 lb.

boxes, 4 slabs/box) Disclaimer: Science Buddies occasionally provides information (such as part numbers, supplier names, and supplier weblinks) to assist our users in locating specialty items for individual projects. The information is provided solely as a convenience to our users. We do our best to make sure that part numbers and descriptions are accurate when first listed. However, since part numbers do change as items are obsoleted or improved, please send us an email if you run across any parts that are no longer available. We also do our best to make sure that any listed supplier provides prompt, courteous service. Science Buddies does participate in affiliate programs with Amazon.com , Carolina Biological , Jameco Electronics , and AquaPhoenix Education . Proceeds from the affiliate programs help support Science Buddies, a 501(c)(3) public charity. If you have any comments (positive or negative) related to purchases you've made for science fair projects from recommendations on our site, please let us know. Write to us at scibuddy@sciencebuddies.org . Share your story with Science Buddies! I Did This Project! Please log in and let us know how things went.

Experimental Procedure Note Before Beginning: This science fair project requires you to hook up one or more devices in an electrical circuit. Basic help can be found in the Electronics Primer . However, if you do not have experience in putting together electrical circuits you may find it helpful to have someone who can answer questions and help you troubleshoot if your project is not working. A science teacher or parent may be a good resource. If you need to find another mentor, try to find someone who has hobbies like robotics, electronics, or building and fixing computers. You may also need to work your way up to this project by starting with an electronics project that has a lower level of difficulty. Wiring the Potentiometers Here are some notes for before you start. Do your background research, and make sure that you are knowledgeable about all of the terms, concepts and questions. To avoid damage to components, the solderless breadboard should be powered off when your are building or making changes to the circuit. Do not turn on the power until the circuit is completed and you have double-checked all of your wiring paths. You'll need some knobs to twiddle, so take care of mounting and wiring your potentiometers first. Wear safety glasses for this step.

A tunafish can makes a good, inexpensive support for the three potentiometers. Mark the center locations for the three holes. Use a center punch or tap a nail with a hammer to make a small depression at the center location so the drill bit won't slip. Drill a 5/16" hole for the shaft of each potentiometer. Go slow with the drill: the metal is thin, and the bit will tend to grab once it goes through. You'll have less problems with burrs if you go slow. Mark and drill a 5/16" hole in the side of the tuna can for running the hook-up wires. Mark the center and drill a 1/8" hole to the right of each shaft hole to accommodate the small mounting tab on the potentiometer. Carefully remove any burrs from the holes with a file. Mount the potentiometers in the can, using the provided washer and nut. Solder wires to the potentiometers (see Figure 5). Use red wire for the +5 V connection. Use black wire for the ground connection.

For the center lug, I used red, green and black for the red, green and blue LEDs, respectively (didn't have any blue wire handy). (For the green and blue potentiometeres, remember that they are left-right reversed when you're working from the bottom!) Figure 5. Wiring the potentiometers. You can daisy-chain the +5 V wire (red) between the pots (right hand lug, when viewed from beneath, as in the photo). You can also daisy-chain the ground wire (black; left-hand lug, when viewed from beneath, as in the photo). The center lug is what goes to the non-inverting input of the op-amp (pin 3). To keep your connections straight, use a wire color that resembles the color of the LED (or label the wires). Add the knobs (Figure 6), and this part is done. Figure 6. Completed potentiometer controls mounted in a tunafish can. Building the Rest of the Circuit Next, you'll build the LED control circuits on the solderless breadboard. You can learn how to use a breadboard in the Science Buddies reference How to Use a Breadboard .

Remember that the power supply for the breadboard should always be off when you are building the circuit! The LF411CN chip used in this project is an example of an integrated circuit (IC). The electronics industry has several different ways of making ICs, so you can often buy the same IC in several different physical formats or "packages." The LF411CN part used in this project is called a "dual inline plastic" (or "DIP") package. A DIP IC has two rows of metal "pins" coming out from each side. Figure 7 shows pin numbering scheme for the LF411 DIP package. The semi-circular depression at one end of the chip marks the "top" end of the chip. In this orientation, pin 1 is at the top left. (This is the electronics industry standard for all DIP packages.) Pin 1 is often additionally marked with a small circular depression. You count pin numbers down the pin 1 side, and then back up the other side.

Thus on an 8-pin DIP, pin 8 is opposite pin 1, pin 7 is opposite pin 2, pin 6 is opposite pin 3, and pin 5 is opposite pin 4. Figure 7. Pin numbering scheme for the LF411 DIP IC. The small semi-circular depression marks the top end of the chip. Pin 1 is at the top left. Often, the chip will also have a small circular depression next to the pin to mark pin 1. You count pin numbers down the pin 1 side, and then back up the other side. Figure 8 shows the schematic for an individual LED control. The numbers 2, 3, and 6 show which pin on LF411 IC chip corresponds to the connection in the schematic. Each LED gets its own control, so you need to make three copies of this circuit on your breadboard. Notice that the schematic does not show the connections for power to the LF411 (V+, pin 4, and V−, pin 7). Figure 8. Schematic of a single LED control circuit (Calvert, 2002).

As described in the Introduction, you insert the LF411 IC into the breadboard so that chip straddles one of the gaps in the rows of holes. Make sure that each of the 8 pins is aligned with its proper hole, then carefully push the chip straight down. The first connections to make are the power supply connections for the LF411. Use jumper wires to connect the +15 V bus to pin 7 and the -15 V bus to pin 4. Next connect the 330 Ω resistor. One end of the resistor connects to pin 2, the other end connects to the ground bus. Use a needle-nose pliers to make 90° bends in the leads at the proper distance, then trim each lead to about 7-8 mm below the bend. Insert the resistor into the breadboard. Next connect an LED. Remember that the longer lead is the anode (+), which connects to pin 6, and the shorter lead is the cathode (-), which connects to pin 2. Use the needle-nose pliers to make a "jog" in the anode so that the ends of the leads are about the same length.

Insert the anode into a hole above pin 6, insert the cathode into a hole beyond the end of the chip. Then use two jumpers to make an electrical path from the LED cathode to pin 2 of the LF411 (see Figure 9). Making the connection this way (rather than having the LED "straddle" the chip) keeps the circuit layout (and the LED leads) neater. A neater circuit has several advantages: You have easier access to circuit points when you want to make voltage measurements with your digital multimeter. The circuit is easier to understand. You are less likely to make wiring mistakes, and more likely to catch them if you do. Figure 9. Detail view of completed circuit on breadboard. Notice how the LF411 ICs span the gap between the holes in the breadboard. Power connections to each chip are made to pin 7 (+15 V) and pin 4 (−15 V). (Our breadboard has only two power bus lines, so we used the blue jumpers to "daisy-chain" the +15 V power connections.

If your breadboard has enough bus lines, direct connections for each chip are preferable.) The 330 Ω resistors are connected between pin 2 of each chip and the ground bus. The anode (+ lead) of each LED connects to pin 6 of the appropriate LF411 chip, and the cathode (− lead) connects to pin 2. Notice how, for each LED, we used two jumpers to connect the cathode to pin 2. The center lug from each potentiometer is connected to pin 3 of the corresponding LF411 chip. The final component to connect is the potentiometer. Connect the +5 V lead for the potentiometers to the +5 V bus. Connect the ground lead for the potentiometers to the ground bus. Connect the center lug of each potentiometer to pin 3 of the corresponding LF411 chip. (Refer to Figure 6). Before you turn on the power for the first time, double-check all of your connections.

Use your digital multimeter to measure the voltage between pin 3 (the output of the 10k potentiometer) and ground, as your assistant turns the knob up and down (if you need help using a multimeter, check out the Science Buddies reference How to Use a Multimeter ). It should vary between 0 and about +5 V (your power supply may deliver a bit more than +5). Be careful to touch only a single pin; if your probe touches two pins at once, you'll short them, and you may destroy the chip. Do the same for pin 2. You should see values similar to what you saw on pin 3 as the potentiometer is turned. (Remember that, with feedback to the inverting input, the op-amp minimizes the voltage difference between its inputs.) As the voltage at pin 2 changes from 0 to +5 V, how does the current through the 330 Ω resistor vary? Notice that this is also the current through the LED. Mixing Colors with the Circuit Your results will be best if you do this step in a darkened room.

In order to mix light from the red, green, and blue LEDs to produce additional colors, you will need to project the light on to some surface. A slab of paraffin wax will work well. The wax is translucent, and it will diffuse the light. A small cardboard box, opened at both ends, will make a good support for the wax slab (see Figure 10). We used a coffee filter box, cut in half (dimensions approximately 12 cm x 4 cm x 10 cm (w x d x h). Tape some cardboard "struts" at the ends of the opening at the top so that the opened box keeps its shape. Figure 10. Cut-off cardboard box, used as support for wax slab. Place the wax slab on top of the box to use the wax as your translucent "projection screen" (see Figure 11). Figure 11. Wax illuminated by red LED. You'll notice that the LEDs appear brightest when you look straight down on them. Try to adjust them so that they project in overlapping circles on the wax. You may have an easier time with this if you solder some wire leads to the LEDs.

Use needle nose pliers as a heat sink when you solder, so that you don't damage the LED. Hold the pliers closed with a rubber band on the handles. Clamp the pliers on the lead near the body of the LED. Do your soldering work on the side of the pliers that is away from the body of the LED. Strip the other ends of the wires so that they can connect to the breadboard. You can use heat-shrink tubing to insulate the exposed metal on the leads. Slide it over the soldered wire to cover the remaining metal, then warm it with a hair dryer to shrink it. Now you can safely bundle the LEDs together without risking a short circuit. Projecting a longer distance should help improve uniformity, but the light intensity will decrease in proportion to the square of the distance. Another trick you can use to get uniform illumination of the wax is to restrict the area of the wax that you can see. Cut a circular hole in a piece of black construction paper and place it over the wax (Figure 12). The size of your cut-out should match the area of uniform illumination on the wax. Figure 12. Restricting the visible area for more uniform illumination.

Start with just one pair of LEDs, for example, red and green. Turn up the red LED part-way and observe the color. Now add a bit of green light. What happens? Add a bit more and see what happens. What different colors can you make by mixing different levels of these two lights? Try all of the possible pairwise combinations, then try with all three LEDs. Share your story with Science Buddies! I Did This Project! Please log in and let us know how things went. Variations For a more basic experiment on color mixing, see the Science Buddies project Mixing Light to Make Colors . Does everyone see the same colors? Here's a way to use your circuit to investigate this question. Make sure that your LEDs are well-aligned, and that the wax slab is masked off with black so that only a uniformly illuminated area is visible. Do the testing in a darkened room. Set the red LED a middle value. Use your DMM to measure the voltage setting for the red LED (either pin 2 or pin 3 on the corresponding LF411), and record it in your notebook. You'll need to start out with this same voltage for the red LED for each test subject.

Have your volunteers adjust only the green LED, until the color that they see is neither green, nor red. They should get a pure color, without any tinge of green or red. When they are finished, use your DMM to measure the voltage setting for the green LED. How close are the values for the green LED across all of your test subjects? For a method for measuring LED output as a function of current, see the Science Buddies project How Does LED Brightness Vary with Current? That project uses a light-to-voltage converter, an IC that contains a photodiode and an op-amp. The photodiode produces a current when exposed to light, and the op-amp produces a voltage proportional to the photodiode current. The photodiode is more sensitive to some wavelengths of light than others, so you'll have to take that into account if you want to compare the brightness of red, green, and blue LEDs. The datasheet for the light-to-voltage converter has a spectral responsivity curve for the photodiode that you can use for this purpose (see the Bibliography section in the linked project).

You can use paraffin wax to make a Joly photometer, a simple device that will allow you to match the intensity (and color) of two light sources. Illuminate one side of the photometer with colored light produced using a colored filter over a flashlight (or slide projector). Can you match the color with light projected from your red, green, and blue LEDs? Try using the color picker for an application on your computer (either the operating system itself, or drawing programs usually have this feature). See what RGB values correspond to particular colors. Can you use this information as a guide to reproduce the colors with the LEDs? Note that on your monitor, as the values get higher, the additional intensity for a given numerical change becomes greater. To learn more about this, look for information on the "gamma function" for computer monitors. If you like this project, you might enjoy exploring these related careers: Electrician Electricians are the people who bring electricity to our homes, schools, businesses, public spaces, and streets—lighting up our world, keeping the indoor temperature comfortable, and powering TVs, computers, and all sorts of machines that make life better. Electricians install and maintain the wiring and equipment that carries electricity, and they also fix electrical machines.

Read more Electrical & Electronics Engineer Just as a potter forms clay, or a steel worker molds molten steel, electrical and electronics engineers gather and shape electricity and use it to make products that transmit power or transmit information. Electrical and electronics engineers may specialize in one of the millions of products that make or use electricity, like cell phones, electric motors, microwaves, medical instruments, airline navigation system, or handheld games. Read more Electrical Engineering Technician Electrical engineering technicians help design, test, and manufacture electrical and electronic equipment. These people are part of the team of engineers and research scientists that keep our high-tech world going and moving forward. Read more News Feed on This Topic , , Note: A computerized matching algorithm suggests the above articles. It's not as smart as you are, and it may occasionally give humorous, ridiculous, or even annoying results! Learn more about the News Feed Looking for more science fun? Try one of our science activities for quick, anytime science explorations. The perfect thing to liven up a rainy day, school vacation, or moment of boredom. Mixing Light to Make Colors Mixing Light to Make Colors No issues Abstract You know how to make new colors by mixing paint or crayons.

For example, you get green by mixing yellow and blue, or orange by mixing red and yellow. With paint, blue, yellow, and red are primary colors, which you can use to make other colors. Have you ever tried making colors with light? Are the primary colors the same ones you use for paint? Do this experiment and find out. Objective The goal of this project is to learn some basic principles of color perception by experimenting with various combinations of colored lights. Credits Andrew Olson, Ph.D., Science Buddies Sources This project is based on: Shields, J., 1993. "Color Perception Experiments for Children," Optics & Photonics News, May, 1993: 69, available online [accessed March 5, 2007] . Cite This Page MLA Style Science Buddies Staff. "Mixing Light to Make Colors" Science Buddies. Science Buddies, 11 July 2015. Web. 19 Jan. 2017 < APA Style Science Buddies Staff. (2015, July 11). Mixing Light to Make Colors.

Retrieved January 19, 2017 from Share your story with Science Buddies! I Did This Project! Please log in and let us know how things went. Last edit date: 2015-07-11 Introduction The process of seeing begins with light-sensitive cells at the back of the eye called photoreceptors. People have two main types of photoreceptors, called rods and cones because of the shapes of the light-sensitive parts of the cells. Rod photoreceptors are more sensitive and respond faster than cones. They are used in dim-light conditions. Cone photoreceptors are essential for color vision. They are used in bright-light conditions. In the central part of the eye there is a circular area packed densely with cone photoreceptors (no rods), called the fovea. This is the region of your eye that you use most of the time. Any visual task that requires seeing fine details (reading the letters on this webpage, for example) uses the fovea. How does color come into this? You've seen white light refracted by raindrops or diffracted by the shiny surface of a CD to make a rainbow of colors. The rainbow shows the spectrum of visible light.

The different colors that you see in a rainbow correspond to light with different amounts of energy. The light at the blue end of the rainbow has slightly more energy than the light at the red end of the rainbow. Figure 1. The visible spectrum. X-rays, light, and radio waves are examples of electromagnetic waves. Light is the part of the electromagnetic spectrum that we can detect with our eyes. Cone photoreceptors have evolved so that they are most sensitive at different regions of the visible spectrum. This forms the basis for our sensation of color (Illustration from Abrisa Glass & Coatings, 2005). At the blue end of the visible spectrum, the wavelength of light is shorter—about 400 nanometers. (A nanometer is 1 billionth of a meter, or 1 x 10-9 meter. The abbreviation for nanometer is 'nm'.) At the red end of the spectrum, the wavelength of light is longer—about 700 nm. Cone photoreceptors have evolved into three different types. Each one is most sensitive to a different region of the visible spectrum.

One type responds best to shorter wavelengths; another responds best to wavelengths towards the middle of the spectrum; and the third type responds best to longer wavelengths. The different cone photoreceptors are not sharply tuned to a particular color, however. So a short-wavelength cone photoreceptor can still respond to longer-wavelength light that falls on it. It is more likely to respond to shorter wavelength light, but it is still possible for it to respond to mid- and long-wavelength light. The signals from the three different types of cones are combined in the retina and in the brain, eventually giving rise to the sensation of color. In this experiment, you will use different combinations of light to investigate color sensation. You will be working with three different lights: red, green, and blue, mixing them in different combinations. If you're only used to making colors with paint, you may be in for some surprises! Terms and Concepts To do this project, you should do research that enables you to understand the following terms and concepts: photoreceptor, To do this experiment you will need the following materials and equipment: 3 flashlights; notes: Any flashlight will work for this project, but it is best if the brightness of each flashlight is about the same.

If you are purchasing flashlights for this project, we recommend the "Mini Maglites" brand ( . These are rugged, have high output, and, most importantly, they can be focused. They are available in many stores, and from multiple online sources. colored filters, notes: you can make your own with transparencies and red, green, and blue colored markers ("Sharpie" brand works well), or you can purchase colored filters online (e.g., a booklet of colored filters for about $20, including shipping: stock #V39417 from Anchor Optics ); three identical, clear drinking glasses, wax paper, red, green, and blue food coloring, water, dark room with a white wall, a screen, or a large piece of white paper taped to the wall, table for holding glasses with colored water, an assistant to help with mixing the three lights. Disclaimer: Science Buddies occasionally provides information (such as part numbers, supplier names, and supplier weblinks) to assist our users in locating specialty items for individual projects. The information is provided solely as a convenience to our users. We do our best to make sure that part numbers and descriptions are accurate when first listed.

However, since part numbers do change as items are obsoleted or improved, please send us an email if you run across any parts that are no longer available. We also do our best to make sure that any listed supplier provides prompt, courteous service. Science Buddies does participate in affiliate programs with Amazon.com , Carolina Biological , Jameco Electronics , and AquaPhoenix Education . Proceeds from the affiliate programs help support Science Buddies, a 501(c)(3) public charity. If you have any comments (positive or negative) related to purchases you've made for science fair projects from recommendations on our site, please let us know. Write to us at scibuddy@sciencebuddies.org . Share your story with Science Buddies! I Did This Project! Please log in and let us know how things went. Experimental Procedure Mixing Colored Lights: Using Colored Filters Attach one colored filter over each flashlight, so that you have one red, one green, and one blue light. In a darkened room, project each light onto the wall separately and observe the color. Now choose two of the lights, for example red and green, and project them onto the wall so that their spots of light overlap.

What color do you see where the spots overlap? What happens if you make one of the lights a little dimmer than the other? There are several ways that you can dim the light: Use your fingers to partially shade the light. Move one of the lights further from the wall than the other. (See the Variations section for an idea on how you can use this technique to estimate the relative brightness of your two light sources.) If your flashlight has a focusing mechanism, you can change the focus of the flashlight. Spreading the beam wider will make the light dimmer. Making the beam narrower will make the light brighter. Repeat steps 3 and 4 with each pair of lights (i.e., red + green, red + blue, and green + blue). With help from your assistant, project all three lights so that their spots overlap. What color do you see where the spots overlap? What happens now when you dim one of the lights? Keep track of your results in your lab notebook. You can use a table to organize your results. Light 1 Mixing Colored Lights: Using Food Coloring in Water Prepare the three glasses with food coloring solution: Fill each glass with water to the same level. Add one drop of red food coloring to the first glass.

Add one drop of green food coloring to the second glass. Add one drop of blue food coloring to the third glass. Note: if you like, you can use more than one drop of food coloring per glass, but use the same number of drops for each color. Wrap each glass with a single layer of waxed paper. The waxed paper will diffuse the light shining through the glass and water, making a more uniform colored light source. Position the glasses on a table near your projection wall so that you can shine light through the glasses and make the projected lights overlap. Darken the room. Now choose two of the glasses, for example red and green. Use two separate white-light flashlights (i.e., no colored filters on the flashlights) to project light through each glass onto the wall. Orient the flashlights so that the projected lights overlap. (To start, each flashlight/glass combination should be the same distance from the wall.) What color do you see where the lights overlap? What happens if you make one of the lights a little dimmer than the other? There are several ways that you can dim the light: Use your fingers to partially shade the light before it passes through the glass.

Move one of the glasses further from the wall than the other. (See the Variations section for an idea on how you can use this technique to estimate the relative brightness of your two light sources.) If your flashlight has a focusing mechanism, you can change the focus of the flashlight. Spreading the beam wider will make the light dimmer. Making the beam narrower will make the light brighter. Repeat steps 3 and 4 with each pair of lights (i.e., red + green, red + blue, and green + blue). With help from your assistant, project all three lights so that their spots overlap. What color do you see where the spots overlap? What happens now when you dim one of the lights? As with the previous experiment, keep track of your results in your lab notebook. You can organize your results in a table similar to the one you used before. Share your story with Science Buddies! I Did This Project! Please log in and let us know how things went. Variations Choose a different set of three filters for your primary colors. What colors can you produce by mixing with your new set of primaries? Use your computer's color picker to see what R, G, B values are needed to produce a chosen color.

Can you make a similar color with your flashlights? For the experiment with food coloring, another way to change the relative intensity of the colors is to change the concentration of the food coloring. What happens if you dilute one of the colors? Take off the wax paper, then pour out 4/5 of the contents of one glass (red, for example). Refill the glass with plain water. Dry off the outside of the glass, and re-wrap it with wax paper. What color do you get now when you mix light shining through all three glasses? What change do you need to make in order to produce white light by combining light projected through each of the three glasses? Do background research on the "inverse square law" to learn how the intensity of a light changes with distance from the light source. Use what you learned to measure the relative brightness of the lights you mix to obtain different colors. For a more advanced color-mixing experiment using red, green, and blue LEDs, see the Science Buddies project Color Mixing with Red, Green, and Blue LEDs . Share your story with Science Buddies! I Did This Project! Please log in and let us know how things went.

Question: Mixing blue, red, and green light produces what colour/color?
Answer: White