Dictionary: Definitions
About this dictionary
This DICTIONARY OF LIGHT, COLOUR & VISION contains a vocabulary of closely interrelated terms that underpin all the resources you will find here at lightcolourvision.org. Each term has its own ...
Absorption
When light strikes an object, some wavelengths are absorbed and their energy is converted to heat, others undergo reflection or transmission. When light is absorbed by an object or medium, ...
Accommodation
Accommodation refers to the way the lenses inside our eyes accommodate for the fact that objects of interest may be close to or at a distance. Sharp images on the ...
Achromatic
Achromatic means without colour so refers to surfaces or objects that appear white, grey or black. Achromatic colours lack hue or saturation but can be described in terms of their ...
Additive colour model
An additive colour model explains how different coloured lights (such as LEDs or beams of light) are mixed to produce other colours. The RGB colour model and HSB colour model ...
Adobe RGB colour space
The Adobe RGB (1998) colour space was developed by Adobe Systems. It aims to ensure the optimal range of colours available within the RGB colour model are accurately reproduced when ...
Airglow
Airglow is a faint, continual emission of light originating from the Earth's upper atmosphere, typically between 80 and 400 kilometres in altitude. While often mistaken for distant starlight, it forms ...
Alexander’s band
Alexander's band, also known as Alexander's dark band, is an optical phenomenon observed in rainbows. It refers to the region between the primary and secondary bows, which often appears noticeably ...
Amacrine cells
Amacrine cells are interneurons in the human retina that interact with retinal ganglion cells and/or bipolar cells. Amacrine cells are a type of interneuron within the human retina. Amacrine cells ...
Amplitude
The amplitude of an electromagnetic wave is directly connected with the amount of energy it carries. In a wave diagram, amplitude is represented as the distance from the center line ...
Analogous colours
Analogous colours are colours that are very similar to one another and appear next to each other on a colour wheel. Analogous colours are colours with similar hues. An example ...
Angle of deflection
When discussing the formation of rainbows, the angle of deflection measures the angle between the initial path of a light ray before it hits a raindrop, and the angle of ...
Angle of incidence
The angle of incidence measures the angle at which incoming light strikes a surface. When light is travelling towards something it is said to be incident to that surface or ...
Angle of reflection
The angle of reflection is the angle between the incident light ray and the reflected light ray, both measured from an imaginary line called the normal. According to the law ...
Angle of refraction
The angle of refraction indicates the extent to which light bends and changes direction as it passes from one transparent medium into another. The angle of refraction is measured between ...
Angular distance
When discussing rainbows, angular distance is the angle between the line from the observer to the centre of the rainbow (rainbow axis) and the line from the observer to a ...
Artificial light source
An artificial light source is any source of light created by humans, as opposed to natural light sources like the sun or stars. Artificial light sources are generated by converting ...
Atom
An atom is the smallest unit of a chemical element that retains all of its physical and chemical properties. At the core of an atom is a nucleus that contains ...
Attributes of visual perception
Attributes of visual perception consist of inherent abilities and skills developed over time that facilitate our understanding of visual information.Attributes of visual perception associated with the response of the human ...
Aurora
Aurora (also known as the polar lights) are natural displays featuring curtains, rays, spirals, and flickering patterns of light in the northern polar latitudes (Aurora Borealis) and southern polar latitudes ...
Bands of colour
An observer perceives bands of colour when visible light separates into its component wavelengths and the human eye distinguishes between different colours. In the presence of a rainbow, an observer ...
Bioelectroluminescence
Bioelectroluminescence is a type of chemiluminescence where the emission of light is specifically produced by a biological process within a living organism. Bioelectroluminescence is a type of chemiluminescence where the ...
Bioluminescence
Bioluminescence is a type of luminescence resulting from the production and emission of electromagnetic radiation by living organisms. Bioluminescence, meaning "living light," occurs in a wide variety of creatures, from ...
Bipolar cells
Bipolar cells are the retinal interneurons that provide the primary pathway from photoreceptors (rod and cone cells) to ganglion cells. In addition to directly transmitting signals from photoreceptors to ganglion ...
Blackbody
An object that absorbs all radiation falling on it, at all wavelengths, is called a blackbody. A blackbody is a theoretical concept for an object that completely absorbs all electromagnetic radiation, regardless ...
Bohr model
The Bohr model of the atom, proposed by Danish physicist Niels Bohr in 1913, represented a significant development in the understanding of atomic structure. It revolutionized the view in classical ...
Brightness
In this resource, the terms brightness and colour brightness have distinct meanings. The first refers to a property of light, and the second to a property of colour as detailed ...
Brightness: HSB colour model
This entry discusses colour brightness in relation to the HSB colour model, where H represents hue, S represents saturation, and B represents brightness. Colour brightness can be understood as the ...
Centreline
In general terms, a centreline is a real or imaginary line that passes through the centre of something, often dividing the object into two halves. In a wave diagram used ...
Charge
Electric charge is a fundamental property of matter that governs its interaction with electric and magnetic fields. Electric charge carriers, protons (+) and electrons (-) are the primary charge carriers ...
Charged particle
In physics, a charged particle is a subatomic particle that possesses an electric charge. This charge can be either positive or negative, and it determines how the particle will interact ...
Chemical bond
A chemical bond is a durable attraction between atoms, ions or molecules that enables the formation of chemical compounds. A chemical bond may result from: The electric force between negatively ...
Chemiluminescence
Chemiluminescence is a type of luminescence where light is emitted as a direct result of a chemical reaction. Unlike other luminescence mechanisms that might involve external energy sources such as ...
Chromatic dispersion
Chromatic dispersion is the process where light, under specific conditions, splits into its constituent wavelengths, and the colours linked with each wavelength become visible to a human observer. Chromatic dispersion ...
Chromaticity
Chromaticity refers to the characteristic of colour when described in terms of hue and saturation, rather than just its wavelength. Chromaticity refers to the quality of a colour that sets ...
Chromaticity diagram
A chromaticity diagram is a two-dimensional visual depiction of all the colours produced by mixing specific primary colours in a particular colour model. This means it shows the range of ...
Chromophore
The chromophore is the part of a molecule that produces its colour. Things appear to have colour because they absorb certain wavelengths of light while reflect others. When wavelengths of ...
CIE
The International Commission on Illumination (usually abbreviated CIE for its French name, Commission internationale de l'éclairage) is the international authority on light, illumination, colour, and colour spaces. It was established ...
CIE (1931) XYZ colour space
A color space is a specific system used to represent and categorize colours. It's essentially a way to define and organize the range of colours that can be perceived by ...
Classical electromagnetism
Classical electromagnetism is a theory of physics that describes the interaction of electric and magnetic fields at macroscopic scales. It was developed in the late 19th century by physicists such ...
Classical physics
Classical physics (or classical mechanics) is a group of physics theories that predate modern, more complete, and more widely applicable theories associated with quantum physics (quantum mechanics). Classical physics describes ...
CMY colour model
The CMY colour model deals with a subtractive method of colour mixing. It can be used to explain and provide practical methods of combining three transparent inks and filters (cyan, ...
CMYK colour model
CMYK is a practical application of the CMY colour model in which black is used alongside the three primary colours (cyan, magenta and yellow) to enable digital printers to produce ...
Colour
The visual experience of colour is associated with words such as red, yellow and blue. Things appear coloured to an observer because colour relates to properties of light that are ...
Colour brightness
Colour brightness refers to how a colour appears to a human observer in terms of the lightness or darkness of its hue. Colour is what humans see in the presence ...
Colour constancy
Colour constancy is the ability to perceive colours as relatively constant, even under changing lighting conditions. Colour constancy refers to the perceptual ability to compensate when changes in illumination would ...
Colour management system
A colour management system is a set of techniques and technologies used to ensure that colours are represented and reproduced consistently across different devices (like cameras, monitors, and printers) and ...
Colour model
A colour model is a system or framework used to understand, organise, and manipulate colour. It ranges from basic concepts, such as the sequence of colours in a rainbow, to ...
Colour notation
Colour notation refers to the codes used by colour models to identify and store colour values in a form recognisable to both computers and humans. RGB Colour Model The RGB ...
Colour of objects
The apparent colour of an object is determined as electrons absorb some wavelengths of light and reflect others. The colour an observer sees corresponds with the reflected wavelengths. In terms ...
Colour profile
In the colour management process, a colour profile is a file containing information that accurately defines a colour space, enabling a device to reproduce the intended range of colours. Industry-standard ...
Colour space
A colour space is a system that defines the gamut of colours available within a specific colour model, the relationship between these colours, and the methods for accurately reproducing them ...
Colour theory
Colour theory underpins all colour models and all forms of colour management. Some theories explain how human beings perceive colour, others provide practical methods for managing colour in both analogue ...
Colour value
Colour values are the sets of numbers and/or characters used by colour models to systematically identify and store colour information in a form of colour notation recognizable to both computers ...
Colour vision
Colour vision is the human ability to distinguish between objects based on the wavelengths of the light they emit, reflect or transmit. The human eye and brain together translate light ...
Colour wheel
A colour wheel is a diagram based on a circle divided into segments and used to explore the effect of mixing adjacent colours. A colour wheel is a perceptual tool ...
Complementary colours
In the context of a discussion of light, complementary colours are pairs of colours that, when mixed together, produce white and when placed next to each other appear to create ...
Compound
A compound is a substance made from the combination of two or more elements and held together by chemical bonds that are difficult to break. The bonds form as a ...
Concept map
A concept map is a visual representation used to organize and display relationships between concepts or ideas. Concepts are typically arranged in a hierarchical structure, with more general or broader ...
Cone cell
Cone cells are one of two types of photoreceptor cells (neurons) in the retina of the human eye. Cones are responsible for colour vision and function best in relatively bright ...
Continuous spectrum
A continuous spectrum refers to a complete, unbroken range of wavelengths of light. A continuous spectrum of light is produced by a light source that emits photons over a continuous ...
Cosmic Microwave Background
The Cosmic Microwave Background (CMB) is a form of electromagnetic radiation dating from an early stage of the universe. is a faint afterglow of the Big Bang, a relic from ...
Coulomb’s law
Coulomb's law describes the interaction between electrically charged particles. It tells us how strong the electrostatic force between them is, depending on their properties and their distance apart. Coulomb's law ...
Crest
A crest is a point on a wave with the maximum value of upward displacement within a wave-cycle. A trough is the opposite of a crest, so the minimum or lowest point ...
Critical angle
The critical angle for light approaching the boundary between two different media is the angle of incidence above which the light is totally internally reflected. Internal reflection is a common ...
Crown glass
Crown glass is a type of optical glass that does not contain lead or iron. It is used in the manufacture of lenses and other tools and equipment concerned with the visible part ...
Device-dependent
Device-dependent digital colour spaces Device-dependent means the colours selected on-screen during production and editing are not matched to the specific equipment used to reproduce them. Device-dependent means the digital colour ...
Dictionary
This DICTIONARY OF LIGHT, COLOUR & VISION contains a vocabulary of closely interrelated terms that underpin all the resources you will find here at lightcolourvision.org. Each term has its own ...
Diffraction
Diffraction of electromagnetic radiation, including visible light, refers to various phenomena that occur when an electromagnetic wave encounters an obstacle or passes through an opening. Diffraction and interference are phenomena ...
Diffuse reflection
Diffuse reflections occur when light scatters off rough or irregular surfaces, such as matte or textured surfaces. The scattered light reflects in various directions, leading to a lack of clear ...
Diffusion
In the field of optics, diffusion refers to situations that cause parallel rays of light to spread out more widely. When light undergoes diffusion it becomes less concentrated. Diffuse reflections ...
Digital printing
Digital printing uses the CMYK colour model to enable cyan, magenta, yellow and black inks to be used to output digital files onto paper and other sheet materials. Digital printers ...
Digital screen
A digital screen (or digital display) is an output device for the presentation visual of information. RGB digital screens are used in TVs, computers, phones and projectors. Digital screens use ...
Dispersion
In the field of optics, dispersion is shorthand for chromatic dispersion which refers to the way that light, under certain conditions, separates into its component wavelengths, enabling the colours corresponding ...
Electric & magnetic fields
Electric and magnetic fields are two aspects of the same fundamental force, the electromagnetic force. The electromagnetic force is responsible for the attraction and repulsion between electrically charged particles, as ...
Electric charge
Electric charge is the physical property of matter that causes it to experience a force when placed in an electromagnetic field. Electric charge can be positive or negative. Like charges ...
Electric field line
An electric field line is a component of a diagram representing an electric field. It is a line that corresponds with the electric field at every point along its length ...
Electrically charged particle
An electrically charged particle is a particle that has a positive or negative charge. Electrically charged particles are associated with the electromagnetic force, which is one of the four fundamental ...
Electroluminescence
Electroluminescence (EL) refers to the phenomenon where light is emitted as a direct result of an applied electric field. Unlike other luminescence mechanisms that rely on chemical reactions or light ...
Electromagnetic energy
Electromagnetic energy refers to the energy transported by electromagnetic waves. The amount of energy carried by an electromagnetic wave is directly proportional to its frequency and inversely proportional to its ...
Electromagnetic field
An electromagnetic field is a physical field that describes the behaviour of electrically charged particles and their interactions. It is a region of space where electric and magnetic forces are ...
Electromagnetic force
The electromagnetic force is one of the four fundamental forces in nature and is responsible for electricity, magnetism, and light. It governs the interaction between electrically charged particles, such as ...
Electromagnetic force: manifestations
The electromagnetic force is a fundamental force that has many different manifestations in the natural world. The force itself cannot be directly observed in the same way that a physical ...
Electromagnetic force: properties
The electromagnetic force is evident at both very small and very large scales. At the microscopic level, it acts between charged particles, such as electrons and protons, within atoms. On ...
Electromagnetic radiation
Electromagnetic radiation refers to the transfer of all forms of radiation through space by electromagnetic waves (or their quanta, photons) . This includes gamma rays, ultraviolet (UV), infrared (IR), X-rays, ...
Electromagnetic spectrum
The electromagnetic spectrum encompasses electromagnetic waves with every possible wavelength (and corresponding frequencies) of electromagnetic radiation, spanning low-energy radio waves through visible light to high-energy gamma rays. The electromagnetic spectrum ...
Electromagnetic wave
All forms of light within the electromagnetic spectrum can be thought of as electromagnetic waves produced by the interplay of their electric and magnetic fields. Electromagnetic waves transport electromagnetic energy ...
Electromagnetism
Electromagnetism is the fundamental force that governs the behaviour of electric and magnetic fields. It encompasses the generation, interaction, and propagation of these fields as electromagnetic waves, and includes the ...
Electron
An electron is a subatomic particle, considered to be an elementary particle, as it doesn't have any known parts or structure within it. In an atom, electrons are arranged in ...
Electron cloud
The concept of electron clouds is part of the quantum mechanical model of an atom. It describes the behaviour of electrons in terms of their probable distribution within 'clouds' of ...
Electron excitation
Electron excitation is a general term for any interaction between a photon (particle of light) and an electron. It refers to the process where an electron in an atom or ...
Electron mass
Electron mass is a fundamental property of electrons, representing the intrinsic amount of matter they possess. It is a measure of the electron's resistance to acceleration. Atomic Structure: The mass ...
Electron orbital
An electron orbital is a region of space around the nucleus of an atom where an electron is most likely to be found. Orbitals are not well-defined paths. They represent regions ...
Electron properties
Electrons are fundamental particles that play a crucial role in the structure and behaviour of matter. Electrons play a crucial role in the production and interaction with light. They are ...
Electron spin
Electron spin is an intrinsic property of electrons, along with their mass and charge. Spin is not a classical rotation. It's a quantum property and shouldn't be interpreted literally as ...
Electron transition
An electron transition is the process by which an electron in an atom or molecule changes its energy level. This means it moves from one orbital (a region of probability ...
Electron-electron interaction
An electron-electron interaction that is mediated by a photon is a process in which two electrons interact with each other through the exchange of a photon. The process is common ...
Electronvolt
An electronvolt (eV) is a unit of energy commonly used in atomic, nuclear, and particle physics to measure the energy carried by individual particles and electromagnetic radiation. It's a convenient ...
Electrostatic & magnetic force
The electrostatic force, also known as the Coulomb force, and the magnetic force, described by the Lorentz force equation, are distinct yet connected manifestations of the electromagnetic force. The electrostatic ...
Element
An element is made up of atoms that are all of the same type. Elements are the building blocks of matter. Atoms are the particles that elements are composed of ...
Elementary particle
An elementary particle ( fundamental particle) is the most basic unit of matter that is not composed of smaller particles. These particles are considered the building blocks of everything in ...
Emission
Emission occurs when an element or compound releases energy as either particles (such as electrons or ions) or electromagnetic radiation (such as photons). This process often results from energy changes ...
Energy
Energy is the capacity to cause change or do work. It exists in various forms, such as kinetic, potential, and thermal energy, and can be transferred between objects or converted ...
Excitation of quantum fields
Excitation of quantum fields are temporary disturbances in underlying quantum fields. Quantum fields are continuous and permeate all of spacetime. They are the fundamental entities in quantum field theory, and ...
Fast medium
The speed at which light travels through different media, such as air, glass, or water, is not a constant. Some media are considered "fast" because light passes through them more ...
Fermat’s principle
In the context of refraction, Fermat's Principle accounts for why light follows the specific path it does when bending at the interface between two media and helps to explain why ...
Field
An electromagnetic field (which includes both electric and magnetic fields) is the region around an object where it can exert a force on another object without direct contact. Electric fields ...
Fluorescence
Fluorescence is a type of luminescence, a light source resulting from the temporary absorption and emission of electromagnetic radiation by certain materials. Fluorescence occurs when these materials "catch" light of ...
Force
In physics, a force is anything that can make an object move differently. It's like a push or a pull that can make an object start moving, stop moving, or ...
Force carrier
Each fundamental force is conveyed by a distinct particle type known as a force carrier. These carriers are responsible for transmitting forces between pairs of particles. Take light as an ...
Fovea centralis
The fovea centralis is the region of the eye that provides the optimal location for forming detailed images. The eyes continuously rotate in their sockets to focus objects of interest ...
Free electron
A free electron is an electron that is no longer bound to a specific atom, allowing it to move freely within a material. Normally, electrons exist in energy levels (orbitals) ...
Frequency
The frequency of electromagnetic radiation (light) refers to the number of wave-cycles of an electromagnetic wave that pass a given point in a given amount of time. Frequency is measured ...
Fundamental force
In physics, fundamental forces cannot be explained through simpler or more elementary interactions, so are regarded as fundamental building blocks of the natural world. The four fundamental forces that account ...
Gamma correction
Gamma correction, also referred to as gamma encoding, is an image processing technique that adjusts the brightness and contrast of an image to achieve a more natural and visually pleasing ...
Gamut
The term gamut or colour gamut is used to describe: The range of colours that a specific device or system can display or reproduce. The range of colours that the ...
Ganglion cells
A retinal ganglion cell is a type of neuron located in the retina of the human eye. It receives visual information from photoreceptors through two types of intermediate neurons: bipolar ...
Geometric raindrop
A raindrop is often represented as a geometrically perfect sphere, an idealized form that rarely exists in reality. This simplification helps in understanding the physics of rainbows, even though actual ...
Gravitational force
The gravitational force, also called gravity, is one of the four fundamental forces in nature. The other forces are the electromagnetic force, the strong nuclear force and the weak nuclear ...
Greyscale colour model
In the context of images, a greyscale model represents a picture using only shades of grey, from pure black to pure white. There's no colour information included. This is commonly ...
Hertz (Hz)
The hertz (symbol: Hz) is a unit used to measure the frequency of electromagnetic waves. It represents the number of wave-cycles per second. One hertz is defined as one cycle ...
Hexadecimal notation
Hexadecimal notation is a system for representing RGB colours. For example, a computer display would use the code #FF0000 to produce a bright red pixel. It is commonly used in ...
Horizontal cell
Horizontal cells are neurons that interconnect with other types of neurons within the retina of the human eye. Horizontal cells are one of several types of neurons found in the ...
HSB colour model
The HSB colour model is similar to the RGB colour model insofar as it is an additive model based on RGB primary colours. The strength of the HSB colour model ...
HSB colour values
HSB colour values (codes) are numeric triplets used in software applications and programming to identify different colours. A numeric triplet is a code containing three parameters that refer to the ...
HSL colour model
The HSL colour model is similar to the HSB model. HSL refer to adjustments that can be made to hue, saturation and lightness to produce different colours. HSB refer to ...
Hue
Hue is one of the three main properties of colour, alongside saturation and brightness and is described using names such as red, yellow, green or blue. Hue refers to the ...
Illuminance
Illuminance refers to the amount of light from a natural or artificial light source that falls on a surface. It is usually used to describe the usable light, regardless of ...
Illumination
Illumination (lighting) is the deliberate use of light to achieve a practical, aesthetic or physiological effect. Illumination can be provided through artificial light sources such as lamps and light fixtures, ...
Incandescence
Incandescence is a source of light that occurs naturally as well as artificially. In artificial applications, incandescence is produced by heating a filament in a light bulb until it glows ...
Incident light
Incident light refers to light that is travelling towards an object or medium. Incident light may come from the Sun, an artificial source or may have already been reflected off ...
Index of refraction
The refractive index (index of refraction) of a medium measures how much the speed of light is reduced when it passes through a medium compared to its speed in a ...
Intensity
Intensity measures the amount of light energy passing through a unit area perpendicular to the direction of light propagation. Intensity measures the amount of energy carried by a light wave ...
Interference
Light interference occurs when two or more light waves interact with one another, resulting in a combination of their amplitudes. The resulting wave may increase or decrease in strength.. A ...
Internal reflection
Internal reflection occurs when light travelling through a medium, such as water or glass, reaches the boundary with another medium, like air, and a portion of the light reflects back ...
Interneuron
Interneurons are a type of neuron found in the nervous system of animals, including humans, which play a role in processing and communicating information. Interneurons can be classified into different ...
Joule
The joule (J) is the unit of energy, work, and heat in the International System of Units (SI). The joule (J) is the unit of energy, work, and heat in ...
Kinetic energy
Kinetic energy is the energy an object has because of its motion. Planets, cars, people and atoms all have kinetic energy due to their motion. When a force is applied ...
Laser
A laser is a light source that can create a narrow and intense beam of electromagnetic radiation. Unlike a flashlight, which has a bulb that emits light in all directions, ...
Lateral geniculate nucleus
The lateral geniculate nucleus (LGN) is a relay centre in the visual pathway from the eye to the brain. It receives signals from the retina via the axons of ganglion ...
Law of refraction
The law of refraction, also known as Snell's law, is a fundamental principle in optics that describes how light bends as it travels between two different materials, such as air ...
Light
Light is a form of energy that behaves as a wave and as a particle (photon). It can travel through space and transparent media like air, water, or glass. Light ...
Light emitting diode
A light-emitting diode (LED) is a semiconductor device that emits light when an electric current flows through it. Electroluminescence is the process where this happens: voltage applied to the semiconductor ...
Light source
A light source is any object that emits electromagnetic radiation within the visible spectrum or other areas of the electromagnetic spectrum. A light source is a natural or man-made object ...
Light sources
Light Sources: Mechanism, examples, and everyday applications Footnote: Cerenkov radiation and Synchrotron radiation are not included in the table because they are not conventionally classified as light sources ...
Light stimulus
Light stimuli trigger physiological responses in living organisms, such as vision, photosynthesis, and circadian rhythms. Different organisms respond differently to light stimuli, depending on the presence or absence of specialized ...
Light wave
Light waves are a name for electromagnetic radiation. They consist of self-propagating waves of electric and magnetic fields that travel through space. This wave motion transports energy but doesn't involve ...
Light-emitting process
A light-emitting process refers to any physical mechanism by which a material emits light. These processes involve the transformation of energy within a material into electromagnetic radiation, which includes visible ...
LMS colour space
The LMS colour space is a practical implementation of trichromatic colour theory that enables the full range of human observable colours to be specified by measuring the responsiveness of the ...
Luminance
Luminance is a measure of the perceived brightness of light reaching the human eye, considering both the amount of light emitted, transmitted, or reflected from a surface and the human ...
Luminescence
Luminescence encompasses all processes by which atoms or molecules emit light. It doesn't specify the intensity, colour, or source of the light. Examples include bioluminescence, chemiluminescence, and electroluminescence. Luminescence refers ...
Luminosity
Luminosity refers to the total amount of light being given off by a source, regardless of the direction. The luminosity of a light source depends on the total amount of ...
Magnetic field
A magnetic field is an aspect of the electromagnetic force. It is the interplay between electric and magnetic fields that gives rise to electromagnetic waves, such as visible light, radio ...
Mass
Mass is a fundamental property of matter and is defined as the amount of matter present in an object and is independent of external factors such as location or the ...
Material
A material is the substances or matter that a thing is made of. Material is a broad term for a chemical substance or mixture of substances that constitute an object ...
Material thing
A material thing is made up of matter, which includes all substances that have mass and occupy space. Matter is composed of atoms and molecules, and its properties include mass, ...
Matter
Matter is anything that has mass and energy and occupies space by virtue of having volume. Matter is the substance that makes up all physical objects and substances in the ...
Medium
In physics and optics, a medium refers to any material (plural: media) through which light or other electromagnetic waves can travel. It's essentially a substance that acts as a carrier ...
Metameric
The term metameric refers to visually indistinguishable colour stimuli that appear the same but have different spectral compositions are called metameric. Metameric stimuli are colour stimuli that are indistinguishable from ...
Momentum
Momentum is a measure of how much mass an object has and how fast it is moving. It is calculated by multiplying the mass of the object by its velocity ...
Monochromatic
Monochromatic refers to light or electromagnetic radiation that consists of a single wavelength or frequency. In simpler terms, monochromatic light is composed of just one colour. The term comes from ...
Müller cell
Müller glia, or Müller cells, are a type of retinal glial cells in the human eye that serve as support cells for the neurons, as other glial cells do. An ...
Natural light source
A natural light source is any source of light that occurs in nature without human intervention or creation. These sources can be celestial objects, atmospheric phenomena, or living organisms. Celestial ...
Nature
Nature, in the broad sense, refers to the physical universe encompassing all living organisms (plants, animals, microorganisms) and non-living entities (such as rocks, water, and atmospheric elements). It includes the ...
Neuron
Neurons are specialized cells that transmit electrical and chemical signals throughout the brain and central nervous system, enabling communication between different parts of the body the central nervous system. Neurons ...
Non-spectral colour
A non-spectral colour is a colour that is not present in the visible spectrum and cannot be produced by a single wavelength or narrow band of wavelengths of light. While ...
Normal
If one line is normal to another, then it is at right angles to it. In geometry, normal (a or the normal) refers to a line drawn perpendicular to a ...
Nuclear reaction
A nuclear reaction involves changes within the nucleus of an atom, resulting in the release of energy and often the emission of particles, as well as electromagnetic radiation. This radiation ...
Object
An object is a physical entity and so a thing that has mass and occupies space. An object, as a physical entity, can be defined by its mass and the ...
Observer
A human observer is a person who engages in observation or watches something. Humans observe themselves, each other and the world around them. The act of observation allows us to ...
Observer effect
The observer effect is a principle of physics and states that any interaction between a particle and a measuring device will inevitably change the state of the particle. This is ...
Opacity
Opacity refers to the extent to which an object or surface hinders or blocks light from passing through and so obstructs light from reaching objects or space beyond. Opacity is ...
Optic chiasm
The optic chiasm is the part of the human brain where the optic nerves partially cross. The optic chiasm is located at the bottom of the brain immediately below the ...
Optic nerve
The optic nerve in the human eye is a cable-like bundle of nerve fibres composed of the axons of ganglion cells, responsible for transmitting visual information to the brain’s lateral ...
Optic radiation
The optic radiation are tracts formed from the axons of neurons located in the lateral geniculate nucleus and lead to areas within the primary visual cortex. There is an optic ...
Optical density
Optical density is a measure of how much a material resists and slows the transmission of light. The optical density of a material is not directly related to its physical ...
Optical illusion
Optical illusions and other visual anomalies are caused by the way the human visual system processes information. Physical illusions Physical illusions result from the limitations and assumptions of the human ...
Optical phenomena
Optical phenomena result from the interactions between light and matter. Optical phenomena include absorption, dispersion, diffraction, polarization, reflection, refraction, scattering and transmission. Optics is the branch of physics that studies ...
Optics
Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics ...
Oscillation
An oscillation is a periodic motion that repeats itself in a regular cycle. Oscillation is a characteristic of waves, including electromagnetic waves. Examples of oscillation include the side-to-side swing of a pendulum ...
Particle physics
Particle Physics is a branch of physics that studies the fundamental constituents of matter and energy and their interactions. Particle physics is an experimental sub-field of quantum mechanics often associated ...
Perceived colour
Perceived colour refers to what an observer sees in any given situation and so is a subjective experience. Our ability to perceive and distinguish between colours is crucial to how ...
Phosphorescence
Phosphorescence is a type of photoluminescence where a material absorbs energy from a light source (like sunlight or UV light) and then emits light at a slower rate, even after ...
Photoluminescence
Photoluminescence is the emission of light from a material after it absorbs light. This process involves exciting the electrons in the material to a higher energy level, followed by their ...
Photometry
Photometry is the science concerned with measuring the human perception of light. Measuring human visual responses to light is not straightforward because the eye is a complex and intricate organ ...
Photon
A photon is a particle that carries electromagnetic radiation. It is the fundamental unit of light. Thinking of photons as particles is useful for understanding the quantum nature of light ...
Photon energy
Photon energy is the energy carried by a single photon. The energy of a photon is directly proportional to its frequency and inversely proportional to its wavelength. The higher the ...
Photon-electron interaction
In photon-electron interactions, a photon can either be absorbed by an electron or scattered by it. During the interaction, the photon transfers some or all of its energy and momentum ...
Photopic curve
A photopic curve is a graphical representation of the sensitivity of the human eye to light under normal, bright lighting conditions. It indicates that the human eye has the strongest ...
Pigment epithelium
The retinal pigment epithelium (RPE) is a layer of pigmented cells located between the retina and the choroid of the human eye that supports the photoreceptor cells (rods and cones).The ...
Pixel
A pixel is the smallest addressable element in a digital image that can be uniquely processed and is defined by its spatial coordinates and colour values. A pixel, also known ...
Plank constant
The Planck constant is a fundamental constant of nature that is denoted by the symbol h. The Planck constant is a measure of the smallest possible amount of energy that ...
Polychromatic
Polychromatic refers to something that contains or displays multiple colours. In various contexts, this can describe anything from art and design to objects in nature that reflect or emit a ...
Potential energy
Potential energy is energy in storage. When potential energy is released it becomes kinetic energy. Potential energy can be converted into other forms of energy, such as kinetic energy, which ...
Power
In physics, power is defined as the rate at which work is done. So power describes how quickly energy is transferred from one system to another when work is done ...
Primary colour
Primary colours are sets of colours from which other colours can be created by blending coloured lights or mixing pigments and dyes. Human perception of colour is based on the ...
Primary rainbow
A rainbow is an optical effect produced by illuminated droplets of water. Rainbows are caused by reflection, refraction and dispersion of light in individual droplets and results in the appearance of an arc of spectral colours. A primary ...
Primary visual cortex
The visual cortex of the brain is part of the cerebral cortex and processes visual information. It is in the occipital lobe at the back of the head. Visual information ...
Prism
In the field of optics, a prism is an object made of glass or other transparent material with flat, polished surfaces. Prisms are often used for experimental purposes to study ...
Propagate
Wave propagation refers to any of the ways in which waves travel. Electromagnetic radiation propagates through space, carrying electromagnetic energy in the form of electromagnetic waves. The propagation of electromagnetic radiation through ...
Propagation
Wave propagation refers to any of the ways in which waves travel. Electromagnetic radiation propagates through space, carrying electromagnetic energy in the form of electromagnetic waves. The propagation of electromagnetic radiation through ...
Pure colour
A pure colour is a monochromatic colour with no added tint or shade and can be produced by a single wavelength of light at full saturation. Any single wavelength of ...
Qualitative
Qualitative refers to a description or analysis of something based on its qualities or attributes, rather than on measurable or quantitative data. Qualitative analysis in physics focuses on the inherent ...
Quantitative
A quantitative measure is a measurement of the quantity of something rather than its quality. In physics, the term quantitative refers to a measurable quantity or physical property that can ...
Quantum Electrodynamics (QED)
Quantum Electrodynamics (QED) is a Quantum Field Theory that describes how electromagnetic interactions work at the quantum level. As a fundamental theory in physics, it specifically deals with the interactions ...
Quantum field
Quantum fields are thought to be the underlying reality of all particles and forces. Quantum fields are the building blocks of the universe and play a crucial role in understanding ...
Quantum Field Theory
Quantum Field Theory (QFT) is a theoretical framework that combines classical field theory, special relativity, and quantum mechanics. Quantum fields are thought to be the underlying reality of all particles ...
Quantum Mechanics
Quantum Mechanics is a theory in physics that provides a lens on the behaviour of matter and energy at the atomic and subatomic scales. It serves as the foundation for ...
Quantum Physics
Quantum Physics is a broad term that encompasses all areas of physics that are governed by the laws of Quantum Mechanics. Fields of Quantum Physics that are relevant to our ...
Radiant energy
Radiant energy and electromagnetic radiation are two terms that refer to the same concept. Both refer to the propagation of energy through space in the form of waves. These waves ...
Radiation
Radiation is energy that comes from a source and travels through space at the speed of light. Radiant energy has an electric field, and a magnetic field and may be ...
Radiometry
Radiometry is the study of how light, carried by electromagnetic waves made up of particles called photons, travels through space. It involves measuring and analyzing the energy (radiant energy) of ...
Rainbow
A rainbow is an optical effect produced by illuminated droplets of water. Rainbows are caused by reflection, refraction (bending) and dispersion (spreading out) of light in individual droplets and results ...
Rainbow colours
Rainbow colours are the colours seen in rainbows and in other situations where visible light separates into its different wavelengths and the spectral colours corresponding with each wavelength become visible ...
Ray
A light ray in a diagram is used to show how light moves and changes when it passes through space and different media. Geometric optics uses the concept that light ...
Ray of light
A ray of light (light ray or just ray) is a common term when talking about optics and electromagnetism. A ray of light is a way of imagining, conceptualising and ...
Ray-tracing diagram
A ray-tracing diagram uses drawing conventions and labels to illustrate the path of light rays as they interact with different media, materials, or objects. Ray tracing diagrams help to understand ...
Reflection
Reflection is the process where light rebounds from a surface into the medium it came from, instead of being absorbed by an opaque material or transmitted through a transparent one ...
Refraction
Refraction refers to the way that electromagnetic radiation (light) changes speed and direction as it travels across the boundary between one transparent medium and another. Light bends towards the normal ...
Refractive index
The refractive index (index of refraction) of a medium measures how much the speed of light is reduced when it passes through a medium compared to its speed in a ...
Rest mass
Rest mass, (also known as invariant mass, intrinsic mass, proper mass, or simply mass) in the case of bound systems, is a fundamental property of a particle or a system ...
RGB colour model
RGB colour is an additive colour model in which red, green and blue light is combined to reproduce a wide range of other colours. The primary colours in the RGB ...
RGB colour notation
RGB colour notation refers to the method used by the RGB colour model to identify and store colour values in a format recognizable to both computers and humans. RGB stands ...
RGB colour values
RGB colour values refer to the numeric codes used in RGB colour notation to define specific colours in a digital image or on a digital display. About RGB colour values ...
RGB colour wheel
A colour wheel is a diagram based on a circle divided into segments and can be used to explore the effect of mixing adjacent colours. An RGB colour wheel provides ...
ROYGBV
ROYGBV are the initials for the sequence of colours that make up the visible spectrum: red, orange, yellow, green, blue, and violet. The visible spectrum refers to the range of ...
RYB colour model
The RYB colour model deals with a subtractive method of colour mixing, commonly used in traditional art and painting where opaque pigments are in use. The three primary colours in ...
Saturation
Saturation refers to the perceived difference between one colour and another in terms of its purity and vividness. The hue of a vivid colour appears to be at full strength ...
Scattering
Scattering occurs when light waves interact with particles or irregularities within a medium, causing the light to change direction. This can happen when light encounters obstacles such as molecules in ...
Scotopic curve
A scotopic curve is a graphical representation of the sensitivity of the human eye to light under low-light conditions, such as at night or in very dimly lit environments. The ...
Secondary colour
A secondary colour is created by mixing two primary colours in equal parts within a particular colour model. The colour space can belong to either an additive colour model, which ...
Secondary rainbow
A secondary rainbow is formed when sunlight undergoes two internal reflections within water droplets, creating an arc with colours reversed from the primary rainbow (violet on the outside, red on ...
Sine
In math, sine (sin) is a trigonometric function that relates an angle to a specific ratio in a right-angle triangle. The sine of an angle is defined as the ratio ...
Slow medium
Light travels through different media such as air, glass or water at different speeds. A slow medium is one through which it passes more slowly. Light travels through a vacuum ...
Snell’s law calculator
To calculate the angle of refraction of an incident ray entering a raindrop enter: The refractive index of air for a ray with wavelength 589.29 nm. n1) = 1.000293 The ...
Solar radiation
Solar radiation is the electromagnetic radiation emitted by the Sun. Solar means of or relating to the Sun. Solar radiation is the energy transferred from the Sun in the form ...
Sonoluminescence
Sonoluminescence is the emission of light from bubbles undergoing rapid changes in pressure within a liquid when irradiated with sound waves. Bubble formation: Sound waves passing through a liquid create ...
Spacetime
Spacetime combines the three dimensions of space (length, width, height) and the one dimension of time into a single four-dimensional continuum. This continuum is often visualized as a flexible fabric, ...
Spectral colour model
The spectral colour model represents the range of pure colours that correspond to specific wavelengths of visible light. These colours are called spectral colours because they are not created by ...
Spectral power distribution
The spectral power distribution (SPD) provides a detailed profile of the light emitted or reflected by a source across the visible spectrum, typically represented as a graph where the x-axis ...
Spectrum
The visible spectrum refers to the range of colours that the human eye can perceive, typically seen when light is refracted through a prism, water droplets, or similar mediums. It ...
Specular reflection
Objects with smooth surfaces produce specular (mirror-like) reflections because light reflects off their surfaces at consistent angles. All objects obey the law of reflection on a microscopic level. If the ...
Speed of light
The speed of light is a measurement of how far a light wave travels in a certain amount time. The speed of light is typically measured in metres per second ...
Standard Model
The Standard Model is the theoretical framework that describes the fundamental particles of nature and the forces that act between them. The Standard Model is a quantum field theory, which ...
Stellar light
Stellar light is the term used to describe the electromagnetic radiation emitted by stars, primarily due to the nuclear fusion of hydrogen atoms occurring within their cores. Unlike traditional sources ...
Strong Nuclear force
The strong nuclear force is one of the four fundamental forces in nature. The other forces are the electromagnetic force, the weak nuclear force and gravity. The strong nuclear force ...
Substance
A substance is a type of matter with uniform properties throughout. This means that a sample of a substance will have the same characteristics regardless of its size. One kind ...
Subtractive colour model
A subtractive colour model explains how different coloured pigments (such as paints, inks, dyes or powders) mix to produce other colours. This concept applies primarily to opaque objects, which don't ...
Sun
The Sun is the star at the centre of our solar system. It is a giant ball of hot plasma held together by its own gravity. Here are some basic ...
Sunlight
Sunlight, also known as daylight or visible light, refers to the portion of electromagnetic radiation emitted by the Sun that is detectable by the human eye. It is one form ...
Tangent
A tangent to a circle is a straight line that touches but does not intersect the circle and is at right angles to a radial line drawn from the centre ...
Temperature
Temperature is closely linked to how objects emit electromagnetic radiation, the energy form that includes light, heat, and radio waves. All objects with a temperature above absolute zero (the coldest ...
Thermal radiation
Thermal radiation is a form of electromagnetic radiation emitted by any object with a temperature above absolute zero (-273.15°C or 0° Kelvin). It's a result of the movement of charged ...
Thermodynamics
The two laws of thermodynamics are fundamental principles that govern the behaviour of energy in the universe. They provide us with essential insights into how energy behaves and is transformed ...
Thermoluminescence
Thermoluminescence is the emission of light from a material when it is heated, following previous exposure to ionizing radiation. Exposure to Radiation: When a material (usually a crystalline solid) is ...
Thermonuclear fusion
Thermonuclear fusion, also known as nuclear fusion, is a powerful process where atomic nuclei combine to form a heavier nucleus. This process releases enormous amounts of energy, millions of times ...
Tone
In colour theory, tone refers to a colour's relative lightness or darkness, independent of its hue (colour) or saturation (intensity). A darker tone of a hue can be produced by ...
Total internal reflection
Total internal reflection occurs when light travelling through a denser medium strikes a boundary with a less dense medium at an angle exceeding a specific critical angle. As a result, ...
Transmission
Transmission refers to the process of electromagnetic radiation passing through a medium. When electromagnetic waves move through a material without being absorbed or reflected, we say they are transmitted. If ...
Transverse wave
A transverse wave is a wave that oscillates up and down, left and right, or in any direction perpendicular to their direction it travels. A transverse wave is a type ...
Triboluminescence
Triboluminescence is the emission of light caused by mechanical stress applied to a material. This stress can be from actions like rubbing, crushing, breaking, or scratching. When a material is ...
Trichromacy
Trichromacy (or trichromatic colour vision) is the form of colour vision possessed by human beings and other trichromats that features three different types of cone cells and one type of ...
Trichromatic colour theory
The foundation of the trichromatic colour theory lies in understanding the physiological basis for the subjective experience of colour. It seeks to explain how our eyes and brains work together ...
Trichromatic colour vision
Trichromatic colour vision, also known as normal colour vision, allows humans and some other animals to distinguish a wide range of colours due to the presence of three types of ...
Tristimulus colour values
Human eyes perceive colour through the response of three types of cone cells: L (long wavelength), M (medium wavelength), and S (short wavelength). Tristimulus colour values are a way to ...
Trough
A trough is the point on a wave with the maximum value of downward displacement within a wave-cycle. A crest is the opposite of a trough, so the maximum or ...
Velocity
In the context of electromagnetic waves, velocity describes the rate of wave propagation, accounting for both its magnitude (speed) and direction. As a vector quantity, velocity provides a full description ...
Viewing angle
The viewing angle of a rainbow is the angle between a line extended from an observer's viewpoint to the bow's anti-solar point and a second line extended towards the coloured ...
Virtual photon
A virtual photon is a theoretical concept in particle physics. Virtual photons are thought to be particles that exist for an incredibly brief time and cannot be directly observed. Their ...
Visible light
Visible light refers to the range of wavelengths of electromagnetic radiation that is perceived as colour by human observers. While the range of visible light is generally considered to be ...
Visible spectrum
The visible spectrum is the range of wavelengths of the electromagnetic spectrum that correspond with all the different colours we see in the world. Human beings don't see wavelengths of ...
Vision
Vision, the human visual system, is a complex interplay between various components of the eye, including the cornea, pupil, lens, iris, retina, and optic nerve. It collaborates to capture, focus, ...
Visual perception
Visual perception is the human ability to see and understand our surroundings by virtue of the sensitivity of our eyes to wavelengths of light across the entire visible spectrum, from ...
Wave
A wave is a disturbance that travels through a medium or space, transporting energy from one point to another. Waves can travel through a medium, like waves rippling across a ...
Wave diagram
A wave diagram is a graphic representation, using specific drawing rules and labels, that depicts variations in the characteristics of light waves. These characteristics include changes in wavelength, frequency, amplitude, ...
Wave function
In Quantum Mechanics, a wave function is a mathematical function that describes the quantum state of a physical system, such as a particle or a collection of particles. A wave ...
Wave-cycle
A wave cycle is the complete up-and-down motion of a wave, from one crest (peak) to the next crest, or from one trough (dip) to the next trough. Visualize a ...
Wave-particle duality
Wave-particle duality is a fundamental concept in quantum mechanics that describes the dual nature of particles, which can exhibit both wave-like and particle-like behaviour. Wave-particle duality refers to the phenomenon ...
Wavefront
Electromagnetic waves that are parallel, share a common starting point, have the same frequency and phase, and move through the same medium, form an advancing wavefront at right angles to ...
Wavelength
Wavelength is the distance from any point on a wave to the corresponding point on the next wave. This measurement is taken along the middle line of the wave. While ...
Weak Nuclear force
The weak nuclear force is one of the four fundamental forces in nature, alongside the electromagnetic force, the strong nuclear force, and gravity. The weak nuclear force played a key ...
White light
White light is the term for visible light that contains all wavelengths of the visible spectrum at equal intensities. The sun emits white light because sunlight contains all the wavelengths ...