Shine colored spotlights on a dark stage and drag the circles together, aim flashlights, or draw with light — wherever light overlaps you see the colors of light adding up.
Light mixing is additive: every light you add sends more light into your eye, so mixes get brighter. Red, green and blue together make white — and every screen you own builds all its colors from just those three.
Choose light colors (up to 3) — a basic color or “Pick a color” for any shade
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Each square is two lights at equal brightness. When the sum is brighter than a screen can show, the color is scaled down keeping its proportions.
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Light adds up
Paint works by taking light away; light works by adding it. Point a red spotlight and a green spotlight at the same patch of a white wall and that patch receives both beams at once — more light than either alone. That is additive mixing, and it is why every overlap on the stage is brighter than the lights that make it, and why red, green and blue together give white rather than the brown you get from paint.
The stage on this page adds the lights in linear light units, the way physical light combines, then converts the total to screen colors. When the sum is brighter than a screen can display, it keeps the proportions between red, green and blue and lowers only the brightness, so you still see the true hue of the overlap.
Flashlights and drawing with light
The second tab gives you a dark wall and a flashlight. The beam follows the pointer, and a click or tap pins it in place, so you can build up the classic three-circle diagram by hand: pin red, pin green so they overlap in yellow, then sweep blue across the middle and watch white appear where all three meet.
Draw with light works like the paint palette but with the opposite result. Each stroke adds one unit of its light to the wall, so crossing a red line with a green one makes yellow, and crossing it with green a second time makes chartreuse, two parts green to one of red. Photographers do the same thing with long exposures, waving colored lights in front of an open shutter, and the overlaps in those photos glow brighter in exactly this way.
Why red, green and blue?
The retina has three kinds of cone cells, often called L, M and S, which respond most strongly to long (reddish), medium (greenish) and short (bluish) wavelengths. Every color you perceive is your brain's reading of how strongly each of the three is stimulated. A red, a green and a blue light can each push mainly on one type of cone, which makes them the most efficient set of three for reproducing the colors we see.
The secret of red + green = yellow
Overlap the red and green lights and the middle turns yellow, yet there is no yellow wavelength anywhere in that light. Yellow light from a sodium lamp and the red-plus-green mixture are physically different, but both stimulate the L and M cones in about the same ratio, so the brain cannot tell them apart. Colors that look identical while being made of different light are called metamers, and every screen relies on them.
Magenta is an even stranger case. It does not appear in the rainbow at all: there is no single wavelength that looks magenta. When red and blue light arrive without green in between, the brain fills in a color of its own — the one you see where the red and blue circles overlap.
Complementary lights make white
Each secondary of light is two primaries together: yellow is red + green, cyan is green + blue, magenta is red + blue. Add a secondary to the one primary it is missing and you have all three, which is white. Red + cyan, green + magenta and blue + yellow are the complementary pairs of light; try them with the presets or in the mixing chart, where those squares come out white.
Brightness matters as much as hue. Turn the green light down to half and overlap it with red: instead of yellow you get orange, because there is now more red than green in the mix. The hard quiz questions use this, with some lights at 50% brightness.
Screens, stage lighting and projectors
Look at a phone or monitor through a magnifying glass and you will see tiny red, green and blue subpixels. Each one only varies its brightness; your eye blends them, exactly like the circles on this stage. A color code such as #FF8800 is simply an instruction for those three: red at full power (FF), green at about half (88) and blue off (00). The HEX field in the color picker uses the same codes.
Stage lighting designers and LED strips work the same way, and so do projectors, which overlap red, green and blue images on one screen. Because the mixing is additive, a projector can never show a black darker than the screen it is shining on — it can only add light.
The colored shadow experiment
With three real lamps — red, green and blue — shining on a white wall from slightly different angles, the wall looks white. Hold your hand in front and something surprising appears: three shadows in yellow, magenta and cyan. Each shadow is where one lamp is blocked, so that patch receives only the other two. Where the red lamp is blocked, green + blue remain: cyan. It is the stage on this page, played in reverse.
How the primaries of light and paint fit together
The two systems are mirror images. The secondaries of light — yellow, cyan and magenta — are exactly the primaries of printing ink. A cyan ink is one that absorbs red and reflects green and blue; a magenta ink absorbs green; a yellow ink absorbs blue. Each ink subtracts one primary of light, which is why overlapping two inks leaves one primary: cyan + yellow ink leaves green light.
Light (additive): red, green, blue → all together make white.
Ink (subtractive): cyan, magenta, yellow → all together make near-black.
Classroom paint: red, yellow, blue → all together make brown.
Your eye has three kinds of color receptors, one most sensitive to each of those regions of the spectrum. When all three are stimulated equally strongly, the brain reports white — the same response it gives to sunlight, which contains every wavelength. Mixing light adds energy, so the result is brighter than any single light.
Why are the primaries of light different from paint?
Because one system adds light and the other removes it. Light primaries are the three that each stimulate one kind of cone; ink primaries are the three that each remove one of those lights. That makes the secondaries of light — yellow, cyan, magenta — the primaries of printing. Classroom red, yellow and blue are a traditional approximation of the ink set.
What does a HEX code like #FF8800 mean?
It is three pairs of hexadecimal digits giving the strength of red, green and blue light from 00 (off) to FF (full, 255). #FF8800 is full red, about half green and no blue — an orange. You can type any such code, or rgb(255,136,0), into the color picker on this page to add it as a light.
Why is magenta not in the rainbow?
A rainbow spreads sunlight out by wavelength, from red to violet. Magenta needs red and blue at once with no green, and no single wavelength does that. It is a color the brain constructs from a mixture, which you can see on the stage wherever only the red and blue circles overlap.
Can I use my own light colors?
Yes. Press “Pick a color”, choose from the gradient or enter a HEX or rgb() code, and add it as a light. It appears in the palette next to the basic colors and can be combined with up to two other lights. Each light's brightness slider lets you test how much of each you need.
How does the light mixing quiz work?
There are 80 questions: 33 easy ones with two lights and 47 hard ones with three. Some lights are at 50% brightness, which changes the answer — red with half-strength green is orange, not yellow. Every answer is exact: the sum of the lights, scaled to the brightest channel, matches the named color precisely.