What color is light

Light and Color

Dispersion

What color is light? The answer lies in a prism (fig.). If a ray of light goes through a prism, it is refracted many times, coming in as well as coming out. Because short-wave light is refracted more than long-wave light, it is fractionalized in its wave components: Colors.

Light is refracted by a prism and fractionalized in the color range of visible light.

Scattering

While dispersion in a prism means that the light is being refracted in equal shares of color, other light phenomena behave differently. The sky appears blue to us because the blue part of the sunlight is scattered more than the other colors. This is due to the size of the molecules: they are the same size as the wavelength of the blue color share in sunlight, but smaller than the green or red wavelength.

Different scattering of colors in water molecules in the atmosphere leads to our blue sky.

Interference

The interference is the third phenomenon of the wave characteristics of light. In daily life, we can observe this phenomenon in oil spills or soap bubbles. It is caused by the overlapping of two waves; this is called interference. Interference can occur constructively or destructively.

Interference is constructive if the amplitudes of both waves strengthen each other (fig.).


Scheme of constructive and destructive interference.

Interference is destructive if the phases of both waves are exactly inverse, i.e. wave 1 is in a wave through and wave 2 in a wave crest. They cancel (Fig.).

The interference phenomenon is visible in oil spills and soap bubbles.

What is the connection between interference and rainbow-colored oil-water-spills or soap bubbles (fig.)? When light makes contact with a slim oil film on the surface of a puddle, it is refracted multiply (like in a prism). Other tan in a prism, it is refracted in its color components directly during admission due to the low density of the oil; at discharge, the color components interfere. At regular intervals, the different color components are extinct according to the principle of destructive interference; thus, only the remaining color can be seen. These colors are called interference colors.

Why are we able to see colors? This question will be addressed in the following section.

Additive and subtractive color mixing

There are numerous theories about colors and color mixing. The two most important principles of color mixing theory are described here. Additive and subtractive color mixing principles are needed to understand why we can see our world in color.

Additive color mixing describes the impression of color which approaches the eye, or, to be precise, the retina. The retina of the human eye has so-called rods other cones. The rods perceive differences in light intensity, the cones are responsible for seeing in color (fig.).

The retina of the human eye includes rods sensitive for differences in light intensity and cones for red, green, and blue color.

3 types of cones can be distinguished: Those sensitive for red, green or blue light. Blue, green and red are, therefore, the primary colors of additive color mixing. Additive color mixing causes the color effect by adding colors. If nothing is added, black is perceived. If all equal shares of all colors are mixed, we receive white. If two colors are added, cyan, yellow and magenta are obtained (fig.). Additive color mixing applies to light emitting bodies like TV or computer. Here, this model is also called R (ed) G (reen) B (lue) model.

Additive color mixing with the primary colors red, green and blue.

Subtractive color mixing is not about light colors but body colors. Thus, not the color that reaches the eye is important but the light components absorbed by a non-self-luminous object (i.e. TV or computers are not included). This color impression is caused, therefore, by subtraction of colors.

Subtractive color mixing - because some colors are absorbed and some reflected, we see the world in color!

We conclude: All bodies have color pigments (coloring particles) which can absorb light. If a surface contains pigments absorbing the blue and green parts of light, we perceive it as red - like an apple. Surfaces with pigments absorbing the blue and red parts of light reflect the green part of light. For the eye, these surfaces appear green (fig.) Because the blue and red light has been "subtracted" by the body pigments. Pigments absorbing green light appear magenta, and those absorbing red light seem cyan. If no color of light is absorbed, the surface appears white, and, accordingly, if all is absorbed we see "black". The objects surrounding us color, the white sunlight and the world appears colorful. The principle of subtractive color mixing is also present in printing, where it is known as the C (yan) M (agenta) Y (ellow) (blac) K model.

Subtractive color mixing with the primary colors cyan, magenta and yellow (CMYK model).

Subtractive color mixing becomes even clearer to you if you look at a lemon which is illuminated by sunlight first, including red, green and blue light, and then by red and blue light, and, finally, by blue light only. Characteristically, the pigments in the lemon peel absorb blue light. The red and green shares of incoming sunlight are reflected and combine to yellow. If blue and red light illuminate the lemon, the lemon seems to be red. And if we have blue light only, the lemon is black because all light has been absorbed.

The animation shows the color of the lemon when exposed to different light colors (red, green, blue - red, blue - blue).

Conclusion:

Light is composed of different colors which have different wavelengths. Dispersion, scattering, and interference of light cause incredible color phenomena. To describe the nature of color mixing, the additive and subtractive model was explained. The former applies for light colors, the latter for body colors.