When a beam of white light, composed of three converging monochromatic sources—red, green, and blue—passes through a slit, it is decomposed into its constituent colors. This results in three distinct vertical bands—red, green, and blue—which are projected onto a screen.
If an obstacle, such as a vertical wooden rod, is placed before the slit, it partially blocks some of the light components. As a result, three vertical stripes—cyan, magenta, and yellow—appear at the location of the slit. These colors are the complements of the original light sources and emerge through subtractive color mixing:
- Cyan appears where red is blocked.
- Magenta appears where green is blocked.
- Yellow appears where blue is blocked.
By moving the rod, one can control which complementary color passes through the slit. This complementary color then cancels out its corresponding primary color behind the slit. For example, if magenta passes through, it eliminates green from the screen.
The concept of additive color mixing can be confusing for those who aren’t familiar with artistic or design principles. This is because people are generally more accustomed to subtractive color mixing, which is how colors blend in the physical world, such as when mixing pigments like paints or inks. In contrast, the additive color model describes how light produces color.
