Dictionary: Summaries
Absorption
Absorption of light occurs when the frequency of the wave matches the frequency of electrons orbiting atomic nuclei in a material. 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
An additive colour model explains how different coloured lights (such as LEDs or beams of light) are mixed to produce other colours. Additive colour refers to the methods used and ...
Adobe RGB (1998) colour space
The general purpose of a colour space is to determine the range of colours available within a specific workflow and may be determined by a user or programmatically. The Adobe ...
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 cell
Amacrine cells are interneurons in the human retina within the eyeball that interact with retinal ganglion cells and/or bipolar cells. Amacrine cells are an example of neurons which are the ...
Amplitude
The amplitude of an electromagnetic wave is directly connected with the amount of energy it carries. In a wave diagram, the amplitude is represented as the distance from the centre ...
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. The angle of incidence is measured between a ray of incoming light and an imaginary line ...
Angle of reflection
The angle of reflection measures the angle at which reflected light bounces off a surface. The angle of reflection is measured between a ray of light which has been reflected ...
Angle of refraction
The angle of refraction measures the angle to which light bends as it passes across the boundary between different media. The angle of refraction is measured between a ray of ...
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 ...
Anti-solar point
On a sunny day, if you stand with the Sun at your back and look at the ground, the shadow of your head will align with the antisolar point. The ...
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 ...
Aurora
Auroras are caused by the interaction between charged particles (such as electrons), ejected from the Sun (solar wind), with the Earth's magnetosphere. The magnetosphere accelerates electrons as they enter the ...
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. The human eye and brain together translate light ...
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
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 below. Brightness (as ...
Brightness: HSB colour model
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 below. Brightness (as ...
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 ...
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
A chromophore is the part of a molecule that produces its colour. Things appear to have colour because they absorb certain wavelengths of light while reflecting others. When wavelengths of ...
CIE 1931 XYZ colour space
The CIE 1931 XYZ colour space (also known as CIE 1931 colour space) was one of the first mathematically defined colour spaces and was adopted by the International Commission on ...
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 perception of colour by an observer results from properties of light that are visible to the human eye. The visual experience of colour is associated with terms like red, ...
Colour brightness
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 below. Brightness (as ...
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 recognizable to both computers and humans. Hexadecimal notation is a system ...
Colour of objects
A material gets its colour as molecules absorb some wavelengths of light and reflect others. The colour an observer sees corresponds with the reflected wavelengths. The part of a molecule ...
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 circular diagram divided into segments, featuring primary colours, and used to visualize the result of colour mixing. Colour wheels can enhance understanding of colour relationships ...
Complementary colour
Complementary colours are colours that when compared with one another appear to be in complete contrast with one another when viewed by an observer. Pairs of complementary colours always involve ...
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 ...
Cone cell
Cone cells, or cones, are a type of neuron (nerve cell) in the retina of the human eye. Cone cells are cone-shaped whilst rod cells are rod-shaped. Cone cells are ...
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 ...
Crest
A crest is the highest point of a wave within a wave-cycle. A trough is the opposite of a crest, so it is the lowest point of a wave in ...
Critical angle
The critical angle for light approaching the boundary between two different media is the angle of incidence above which it undergoes total internal reflection. The critical angle is measured with ...
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 ...
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. When microscopic features on a surface are significantly larger than the individual wavelengths of light within the visible spectrum, ...
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 and magnetic fields
Electric and magnetic fields are two interrelated aspects of the electromagnetic force, a fundamental force of nature. This force governs the attraction and repulsion between electrically charged particles, and its ...
Electric field
Electric fields are a property of photons. These dynamic fields, along with corresponding magnetic fields, are responsible for the transmission of electromagnetic energy, such as visible light. Photons are massless ...
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
Ectromagnetic 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, responsible for various phenomena including electricity, magnetism, and light. It governs the interaction between electrically charged particles, such ...
Electromagnetic radiation
Electromagnetic radiation is a type of energy more commonly simply called light. Detached from its source, it is transported by electromagnetic waves (or their quanta, photons) and propagates through space ...
Electromagnetic spectrum
The electromagnetic spectrum includes electromagnetic waves with all possible wavelengths of electromagnetic radiation, ranging from low-energy radio waves through visible light to high-energy gamma rays. There are no precisely defined ...
Electromagnetic wave
An electromagnetic wave carries electromagnetic radiation. An electromagnetic wave is formed as electromagnetic radiation propagates from a light source, travels through space and encounters different materials. Electromagnetic waves can be ...
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 a part of the quantum mechanical model of the atom, which describes the behaviour of electrons in terms of probability distributions rather than fixed ...
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 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-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 ...
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 a property of matter and fields, which can be transferred between systems or transformed into different forms but cannot be created or destroyed. Everything contains energy including all ...
Fast medium
Light travels at different speeds through various media, such as air, glass, or water. A "fast" medium is one where light moves more quickly compared to other materials. In a ...
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. Photoelectric Effect: Free electrons are involved in ...
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 cell
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 colour model represents a picture using only shades of grey, from pure black to pure white. There's no colour information included. This is ...
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. Both RGB and HSB are additive colour ...
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 (lighting) is the deliberate use of light to achieve a practical, aesthetic or ...
Incident light
Incident light refers to light that is travelling towards an object or medium. Incident light refers to light that is travelling towards an object or medium. Incident light may come ...
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). One joule is equal to the amount of work done when a ...
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
As light crosses the boundary between two transparent media, the law of refraction (Snell's law) states the relationship between the angle of incidence and angle of refraction of the light ...
Light
Light is electromagnetic radiation (radiant energy), which, detached from its source, is transported by electromagnetic waves (or their quanta, photons) and propagates through space. Even if humans had never evolved, ...
Light emission
Light Emission refers to the process by which light (electromagnetic radiation) is produced and emitted by a source. This can occur through various mechanisms, depending on the nature of the ...
Light source
A light source is a natural or man-made object that emits one or more wavelengths of light. The Sun is the most important light source in our lives and emits ...
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 another 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 diode (LED)
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 ...
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 ...
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 created when electric current flows. The greater the current the stronger the magnetic field. Whilst an electric field is created by a change in voltage (charge), ...
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 through which light or other electromagnetic waves can travel. It's essentially a substance that acts as a carrier for these ...
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 cells
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 ...
Nanometre
A nanometre (nm) is a unit of length in the metric system, equal to one billionth of a metre (1 nm = 1 × 10⁻⁹ metres). It is commonly used ...
Natural light
A natural light source refers to any source of light that occurs in nature and is not created by human activity. The Sun is the most prominent and important natural ...
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 ...
Newtonian mechanics
Newtonian mechanics is a branch of physics that describes the motion of objects under the influence of forces. It is based on the three laws of motion developed by Isaac ...
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 material thing that has mass and occupies space. An object, as a physical entity, can be defined by its mass and the space it occupies. Objects ...
Observer
A human observer is a person who engages in observation by watching things. In the presence of visible light, an observer perceives colour because the retina at the back of ...
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 prevents light from passing through, thereby obstructing light from reaching objects or space beyond. Opacity is influenced by factors ...
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 consists of neural tracts formed by the axons of neurons in the lateral geniculate nucleus (LGN), which project to the primary visual cortex. There are two optic ...
Optical density
Optical density is a measure of how much a material resists and slows the transmission of light. The higher the optical density of a material, the slower light travels through ...
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 ...
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 (such as sunlight or UV light) and then emits light at a slower rate, even ...
Photoluminescence
Photoluminescence is the emission of light from a material after it absorbs light. The 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 well-lit conditions, such as during the day or in brightly lit environments. The ...
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) ...
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, or a ...
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 ...
Polarization
Polarization of electromagnetic waves refers to the direction in which they oscillate, perpendicular to the direction of the wave's propagation. Polarization can be induced in light waves by various means, ...
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, such as kinetic energy, which is the ...
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 a set of colours from which others can be produced by mixing (pigments, dyes etc.) or overlapping (coloured lights). The human eye, and so human perception, is ...
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 result in the appearance ...
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 is any of the ways in which waves pass through a vacuum or medium. Electromagnetic radiation propagates through space, carrying electromagnetic energy in the form of electromagnetic waves ...
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 ...
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 analysing 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 result ...
Rainbow axis
The rainbow axis is an imaginary straight line that connects the light source, observer and anti-solar point. The centre of a rainbow is always on its axis. The centre of ...
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 ...
Reflectance
The reflectance of the surface of a material is its effectiveness in reflecting radiant energy. Reflectance is the fraction of incident electromagnetic power that is reflected at the boundary. Power ...
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. Colour values are numbers ...
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 is a subtractive method of colour mixing commonly used in traditional art and painting with opaque pigments. The three primary colours in RYB are red, yellow, ...
Saturation
Saturation refers to the perceived difference between one colour and another in terms of its purity and vividness. A fully saturated colour appears bright and vibrant because it has a ...
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 atmospheric molecules, ...
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 mathematics, the sine is a trigonometric function of an angle. The sine of an acute angle is defined in the context of a right-angle triangle. For any specified angle, it's sine is the ratio of ...
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. Electromagnetic radiation is a type of energy that is commonly known as light. Detached from its source, it is transported by electromagnetic waves ...
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 (spectral distribution) of a light or colour stimulus refers to the range, mixture and intensity of wavelengths of light that it produces. A diagram showing the ...
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 the human eye can perceive, typically seen when light is refracted through a prism, water droplets, or similar mediums. It spans ...
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 (or velocity) of a light wave is a measurement of how far it travels in a certain time. The speed of light is measured in metres per second ...
Standard Model
The Standard Model is a quantum field theory, which means it uses the principles of quantum mechanics to describe the behaviour of matter and energy at the atomic and subatomic ...
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 substance sample will have the same characteristics regardless of its size. One kind of substance ...
Subtractive colour model
A subtractive colour model combines different hues of a colourant such as a pigment, paint, ink, dye or powder to produce other colours. CMYK is a subtractive colour model. CMYK ...
Sun
The Sun is the star at the centre of our solar system. The energy emitted by the Sun is called electromagnetic radiation or solar radiation. The solar radiation that the ...
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 ...
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 the 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 is the form of colour vision (trichromatic colour vision) possessed by human beings and other trichromats. It involves three different types of cone cells and one type of rod ...
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 three types of cone cells: L (long-wavelength sensitive), M (medium-wavelength sensitive), and S (short-wavelength sensitive). Tristimulus values quantify colour by representing the levels of stimulation ...
Trough
A trough is a 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 magnitude (speed) and direction. As a vector quantity, velocity provides a full description of ...
Viewing angle
When looking at a rainbow, the viewing angle 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 ...
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 light
Visible light is the range of wavelengths of electromagnetic radiation perceived as colour by human observers. Visible light is a form of electromagnetic radiation. Other forms of electromagnetic radiation include ...
Visible spectrum
The visible part of the electromagnetic spectrum is called the visible spectrum. The visible spectrum is the range of wavelengths of the electromagnetic spectrum that correspond with all the different ...
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. As light travels through the air ...
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 ...
Visual perception
Colour is not a property of electromagnetic radiation, but a feature of visual perception by an observer. The human eye and so human visual perception are tuned to the visible spectrum ...
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 ...
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, depending on the situation. For example, ...
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 ...
Work
In physics, work is defined as the transfer of energy that occurs when a force is applied to an object, causing it to move in the direction of the force ...
Workflow
A workflow is a series of tasks arranged in a specific order to achieve a goal effectively and efficiently. By planning and organizing a workflow, you can ensure no important ...