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Radiation, Light, Color

Updated: Apr 26, 2022

In this post, we will explain some of the basic theories of the generation and behavior of light and colors.

We 3D Artists love every 3D software no doubt. As we ricochet from 3DS Max to Maya, Houdini, Unreal with our monkey appetite, we discover both similarities and differences of those softwares.


However, some basic information is fixed in all software relied on physics. There are many constants such as light, color, reflection, refraction, opacity, transparency, sss etc. We will first try to explain these constants in a clear way.



Light


First and foremost constant is light. So what is it? How it is generated? Is it edible? With one word, It is radiation. Now, before you reach to your biohazard masks lets explain the radiation basically. Meaning is pretty self explanatory. Radiating heat, light energy. Everything in the universe, from galaxies to subatomic particles, is in motion/vibration and the movement naturally releases energy. When you dip your finger in water regularly, you can see how the resulting energy spreads/radiates out in waves. At this point, let us specify two properties of energy, Emitter (source), the thing that brings out the energy, movement of our finger.

Second is Transmitter (intermediary) is the atoms that take the energy from our movement and transfer their excess energy to their neighbors in order to get out of their unstable energy and become stable again. Keep the wave, emitter, transmitter in mind and let's continue with the radiation.



Radiation is basically studied under four sections:

  • Electromagnetic radiation

  • Particle Radiation

  • Acoustic Radiation

  • Gravitational Radiation

All energy radiations are transmitted in the form of waves, particles, or wave/particle duality.


To keep it short, Electromagnetic Radiation is the one responsible from the light.


The sun, as a result of nuclear fusion (merging of atoms) that continues unceasingly in/on its surface, creates a thousand kind of energy. Thanks to electromagnetic radiation which makes the sun is the only light/heat source of our planet and the celestial system we are in.

This light/energy is transmitted to us in superimposed waves, as in the example of water. (Solve the wave/particle duality between you and your physics teacher, we will deal with the wave as we are beach, sun, sea people.)


Color


Colors are generated depending on the wavelength of light/energy. 7 primary colors have unique wavelengths and interpolated wl's between. Let me state briefly that the wavelength is not the height of the waves appearing in the water example, but the distance between the two wave summits. Wavelength is usually measured in nm (nanometers).


1 nm = 0.0000001 cm.

The wavelengths of visible light are between 380 nm and 760 nm.





After the wavelength, let's summarize the frequency, which is inversely correlated to the wavelength. Frequency is the number of waves that pass through a given point in one second. Frequency is expressed in hertz in most cases. 1 hertz means 1 wave pass in a second.

1 Khz (Kilohertz) 1.000, 1Mhz (Megahertz), 1.000.000, 1Ghz (Gigahertz) 1.000.000.000 and 1 Thz (Terahertz) 1.000.000.000.000 passes.


The frequency of visible light is between 400–790 terahertz.


We mentioned inversely correlated. As the frequency increases, the wavelength decreases. As the wavelength increases, the frequency decreases.






Sunlight or white light contains wavelengths of all colors (Sun is white). When we point a flashlight on a prismatic glass, we can see that the light separates and reveals the primary colors which is called dispersion. We will see this another post.


Relationship between color, wavelength and frequency can be seen in the picture:






Let's examine the important points in the picture;


Red is the visible color with the lowest energy/frequency and widest wavelength.

Violet is the visible color with the highest energy/frequency and narrowest wavelength.


Infrared waves are in such high dimensions that we cannot perceive them with the naked eye. When we leave the optical spectrum and inspect radio waves and beyond, a single wavelength can be larger than the diameter of Jupiter. Because it endures long distances and time, red and infrared colors are dominant colors in the universe. Our eyes fliters those exceeding colors out and this way we can see natural balanced colors.

Try to remove IR cut filter from any DSLR and see the resulting very reddish picture.



Ultraviolet waves are also in such low dimensions that we cannot perceive them with the naked eye. However, UV, X, Gamma rays in the optical spectrum cause serious biological damage due to the very high energy they carry. Fortunately, the vast majority of such rays do not pass through the atmosphere. When we are getting roasted in the beach, this is simply because of the ultraviolet enery that reaches to the earth which I remind you most of the rays are rejected/absorbed/reflected by the atmosphere. Imagine if they are allowed in...


Now time to real deal. Does the color we perceive come from the object or from the light?



According to the common and accepted view, the colors we see in objects come not from the objects themselves, but from the light reflecting from the object. Lets try to explain process. Imagine an orange orange. This orange consists of various atoms, electrons and vibrations of these electrons. Remember, vibration = frequency, wavelength. When we point out a white light to the object, two things happens at the molecular level.


First, when colors such as blue, indigo, and purple (other side of the spectrum) interact with an electron that matches their frequency, these waves are absorbed by the particle and the majority of the electrons in the object vibrate appropriately with the frequencies of these colors. Conversely, the majority of electrons in the object vibrate discordantly with green, yellow, orange, and red frequencies. When the frequencies do not match, the incoming energy is returned, which is called reflection. In this way, orange and the wavelengths around it become the only colors that reflected from the object. Our eyes perceive the object as orange. It is that simple. Is it??


Now, just to confuse you, let me briefly talk about another theory. At the beginning, we mentioned that all objects and particles are in motion/vibration which causes radiation in different wavelengths. One of the simpler known examples is the phenomenon called bioluminescence.



Radiation emitted by planktons. The long exposure is for enhancing the effect of the glow and for artistic purposes. It is visible to naked eye too. Some deep ocean creatures has more dramatic bioluminescence.


If we take it one step further, the human body has a similar feature. It emits light in the visible spectrum. Click for the related research.


Enough. I'm bored. In our next article, we will discuss the interaction of light with objects (reflection, refraction, etc.).

Stay safe.



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