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.
Two lights are arranged above a white sheet of paper. When the lights are turned on they illuminate the entire sheet of paper as seen in the diagram below. Each light bulb emits a primary color of light - red R , green G , and blue B. Depending on which primary color of light is used, the paper will appear a different color. Express your understanding of color addition by determining the color that the sheet of paper will appear in the diagrams below.
Suppose that light from a magenta spotlight and light from a yellow spotlight are mixed together, will white light be produced? The magenta spotlight can be thought of as a combination of red and blue light in equal intensities and the yellow spotlight is equivalent to a combination of red and green light in equal intensities. Observe the double abundance of red. Combining the light from the magenta and yellow spotlights will produce a whitish-red color - that is, pink. Physics Tutorial.
My Cart Subscription Selection. Student Extras. 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. When we add all of the different wavelengths of sunlight, we see white light rather than many individual colors. It is called additive because all of the wavelengths still reach our eyes.
It is the combination of different wavelengths that creates the diversity of colors. Subtractive color mixing is creating a new color by the removal of wavelengths from a light with a broad spectrum of wavelengths.
Subtractive color mixing occurs when we mix paints, dyes, or pigments. When we mix paints, both paints still absorb all of the wavelengths they did previously, so what we are left with is only the wavelengths that both paints reflect. It is called subtractive mixing because when the paints mix, wavelengths are deleted from what we see because each paint will absorb some wavelengths that the other paint reflects, thus leaving us with a lesser number of wavelengths remaining afterward.
So the easy way to remember the difference between additive and subtractive color mixing is that additive color mixing is what happens when we mix lights of different colors whereas subtractive color mixing occurs when we mix paints or other colored material.
Use this activity to explore color mixing and its various properties. To see the illustration in full screen, which is recommended, press the Full Screen button, which appears at the top of the page. The first two digits are the brightness of a red pixel, the next two that of the green, then that of blue.
The right hand part of the picture is a close-up of a computer screen, which magnifies the red, yellow, white, magenta intersection.
Looking at the right picture, at top left we see that only red components of each pixel are lit. At top right, both red and green are lit and, from a distance, these appear yellow as in the picture at left.
At bottom right, red, green and blue are all lit and the combination centre of left picture is a convincing white. If you have the room to move ten metres or so back from your screen, you'll see that the sections of the picture on the right really do become red, yellow, white and magenta though the white is less bright than the surrounding white. If you'd like to examine this more closely, here are original close-up photographs courtesy Noel Hanna for the same illustration shown on a computer monitor and a smart-phone.
If you download these files, you can zoom out or in or walk backwards and forwards to see the effect. The photoreceptors in your retina that respond to colour come in just three varieties, which we call 'red', 'green' and 'blue' according to the colour which produces maximal response. On the diagram at top right, the proportional response of the 'red', 'green' and 'blue' photoreceptors is shown as a function of wavelength.
A three-colour representation of a spectrum is shown below the graph. Suppose that light from the yellow region of the spectrum, with a wavelength of say nm, arrives at the retina. It lies between that of red say nm and green nm , so this light stimulates both red and green photoreceptors.
This evokes a sensation that we are taught to call yellow. However, yellow that you see on the monitor is not light with wavelength near nm. Instead, the monitor makes yellow colour using red light and green light from the same pixel. These two different wavelengths from the monitor are focussed onto a small area on your fovea, where it also stimulates red and green photoreceptors. So we perceive the effect as similar to light with wavelength nm, even though no light of this wavelength is present.
We can't show you the difference, because you are probably looking at a RGB screen and it can only show you light with three wavelengths. No matter what we do, we can't get it to produce nm! Many species of insects and birds have four-colour vision, often with sensitivity to near ultraviolet light.
Some flowers have petals that are patterned in the UV but which appear homogeneous to us. A four colour vision system Additive colour mixing by projection Let's look at other ways of adding colours. In this movie, we use three slide projectors, with red, green and blue filters. We vary the intensity in each successively. Depending on your screen, your eyes and your vocabulary, you'll probably see that, once again, red plus green light makes yellow, green plus blue light makes cyan, blue plus red light makes magenta.
One way of combining colours, without a computer monitor, is to illuminate a rotating wheel whose sectors are painted in different colours. The eye integrates light over a few tens of milliseconds, so in that sense it adds the colours that are successively presented at a given point on the retina. We demonstrate that here, using a drill to rotate the wheel. Here, the combination of colours cannot be brighter than the average of all of the colours so, on the monitor, it appears grey rather than white.
Of course, if we compare grey in bright light and white in dim light we may not see a difference. We all remember our first set of paints: red paint plus green paint do not make yellow!
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