★ KAI ★
Kai Jerzö
‘Jerzovskaja’
– Welcome to the here and now –
★ Perceiving and designing ★
Colour (3): Physics and Optics
Optics is a central branch of physics and essential for understanding vision and colour theory. This chapter is dedicated to the physical principles of light and its influence on colour perception.
Light and Colour
Two fundamental models are used to describe light and colour: the particle model and the wave model. Both are essential for understanding the physical properties of light and its interactions.
A. Light as a Particle – The Particle Model
Isaac Newton (1643–1727) experimentally demonstrates in 1676 that white light can be split into seven spectral colours – red, orange, yellow, green, blue, indigo, and violet. He describes light as tiny particles (so-called corpuscles) that move in straight lines. Newton explains reflection and refraction through the interaction of these particles with surfaces.
However, the particle model cannot explain phenomena such as interference and diffraction, which are typical of waves.
B. Light as a Wave – The Wave Model
Christiaan Huygens (1629–1695) develops the wave model, according to which light spreads as a wave in a hypothetical “ether”. Light therefore behaves like an electromagnetic wave, which can interfere and amplify or cancel out.
Thomas Young (1773–1829) proves with the double-slit experiment in 1801 that light produces interference patterns – evidence of its wave nature. Light can thus be described as an electromagnetic wave, which can overlap and either amplify or cancel each other out.
C. Colour Perception – The Trichromatic Theory
In 1827, Thomas Young formulates the hypothesis that human colour perception is based on three types of receptors in the eye, each sensitive to red, green, and blue-violet. Light of different wavelengths is perceived as different colours, while the mixture of these primary colours produces all other colour sensations.
D. Light as a Quantum Phenomenon – The Wave-Particle Duality
The works of Newton and Young form the basis for today’s understanding of light. James Clerk Maxwell proves in 1865 that light is an electromagnetic wave that does not require ether.
Albert Einstein demonstrates in 1905 that light also has particle properties, introducing the concept of “photons” to explain the quantum nature of light. A photon is a light particle – the smallest unit or “quantum” of light – and other electromagnetic radiation, carrying a specific amount of energy and interacting with matter in this way. Depending on how it is observed, the photon either shows wave-like or particle-like properties – a phenomenon known as wave-particle duality.
Photons do not have fixed properties. They can appear as either a wave (in interference and diffraction) or a particle (when interacting with matter), depending on the experiment. However, this does not mean that the photon “switches” between the two states, but rather that the way it interacts with its surroundings depends on how it is measured.
A fascinating aspect is that the state of a photon remains indeterminate until it is measured. The observation process can influence this state – known as the Copenhagen interpretation of quantum mechanics. In a sense, it can be said that the state of a photon is “determined” only through measurement. However, it remains unclear whether the observed energy “emerges” through the measurement process itself.
Light is therefore described as a phenomenon that does not have fixed, classical properties but behaves differently depending on the measurement – a continuous, dynamic state of indeterminacy and interaction. Einstein uses the concept of photons to explain why light with certain wavelengths can dislodge electrons from a metal surface, while light with other wavelengths cannot. The energy of a photon directly depends on its wavelength: shorter wavelengths (e.g., UV light) carry more energy per photon than longer wavelengths (e.g., infrared light).
Visible Light – The Electromagnetic Spectrum
[ Fig. 1: Tabular representation: Wavelength ranges in the electromagnetic spectrum, including visible light (380–750 nm). Fig. 2: Prism: Schematic representation of light refraction and splitting into spectral colours. Fig. 3: Spectrum of the rainbow: Representation of the colours visible to the eye, ranging from blue-violet to red. ]
The Range of Visible Light
The electromagnetic spectrum encompasses wavelengths from very short cosmic rays to long-wavelength radio waves. The visible light range, which is perceivable by the human eye, occupies only a small portion between infrared thermal radiation and ultraviolet radiation, extending from approximately 380 nm (blue-violet) to approximately 750 nm (red).
Colour Perception and Wavelength
- Blue-violet: ca. 380–450 nm (kurzwellig)
- Green: ca. 500–570 nm
- Red: approx. 700–750 nm (long wavelength)
Each wavelength is perceived as a specific colour by the receptors (photoreceptor cells) in the eye.
Refraction of Light and Spectral Colours
The splitting of white light into its spectral colours becomes visible when it is refracted through a prism or water droplets, as in a rainbow. The spectral colours are spectrally pure and cannot be further divided.
As light passes through a prism, it is refracted twice – once when entering and once when exiting. Because different wavelengths are refracted by different amounts, a continuous spectrum is created. This spectrum contains about 300 colour nuances, demonstrating that white light is a mixture of all wavelengths.
Frequency Ranges in the Electromagnetic Spectrum
Ordered from short to long wavelength:
- Cosmic rays
- Gamma rays
- X-rays
- Ultraviolet radiation
- Visible light (“spectrum”)
- Infrared radiation
- Microwaves
- Ultrashort waves
- Short waves
- Medium waves
- Long waves
Summary
Light exhibits both particle and wave properties and can be described as a quantum phenomenon. Colour perception is based on the absorption of specific wavelengths by the receptors in the eye and their processing in the brain. Optics connects physical, physiological, and mathematical approaches to explain the phenomenon of light and its colour perception.
– KAI
© Kai Jerzö, 7th December 2024 –
Citation
Quote? Yes, with pleasure as follows:
– Jerzö, Kai (2024): ‘Perceiving and shaping – Competence in Colour Design: Physics and Optics.’ 2024-12-07. In: Illustration.world-Blog, 2024-12-07. URL: https://illustration.world/design_competence_colour_3_en/ .
