Dictionary tag: F-G-H-I-J

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 retina of the human eye. The other types include photoreceptor cells (rods and cones), bipolar cells, amacrine cells, and ganglion cells.
  • Horizontal cells interconnect with rod and cone cells via synapses, which is why they are often referred to as laterally interconnecting neurons.
  • Horizontal cells help to integrate and regulate photoreceptor cells, cleaning up and globally adjusting signals passing through bipolar cells toward the region containing ganglion cells.
  • An important function of horizontal cells is enabling the eye to adjust to both bright and dim light conditions. They achieve this by providing feedback to rod and cone photoreceptors about the average level of illumination falling onto specific regions of the retina.
  • Horizontal cells are believed to prevent signals representing the brightest objects in a scene from dazzling the retina and degrading the quality of information.

Horizontal cells

Horizontal cells

Horizontal cells are connected to rod and cone cells by synapses and are classed as laterally interconnecting neurons.

Horizontal cells help to integrate and regulate information received from photoreceptor cells, cleaning up and globally adjusting signals passing through bipolar cells towards the regions containing ganglion cells.

An important function of horizontal cells is enabling the eye to adjust to both bright and dim light conditions. They achieve this by providing feedback to rod and cone photoreceptors about the average level of illumination falling onto specific regions of the retina.

If a scene contains objects that are much brighter than others, then horizontal cells are believed to prevent signals representing the brightest objects from dazzling the retina and degrading the overall quality of information.

Caption

The Neuronal Organization of the Retina Richard H. Masland
https://www.cell.com/neuron/fulltext/S0896-6273(12)00883-5?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0896627312008835%3Fshowall%3Dtrue

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 models with red, green and blue primary colours. But whilst RGB relies on directly adjusting the amount of red, green and blue light needed to produce other colours the HSB colour model relies on adjusting hue, saturation and brightness.
  • Hue refers to the perceived difference between colours and is usually described using names such as red, yellow, green, or blue.
    • Hue can be measured as a location on an HSB colour wheel and expressed as a degree between 0 and 360.
  • Saturation refers to the vividness of a colour compared to an unsaturated colour.
    • Saturation is measured between a fully saturated colour (100%) and an unsaturated colour (0%)that appears either:
      • Dull and washed out until all colour disappears, leaving only a monochromatic grey tone (0%).
      • Misty or milky the nearer they are to white.
    • On many HSB colour wheels, saturation decreases from the edge to the centre.
  • Brightness refers to the perceived difference in the appearance of colours under ideal sunlit conditions compared to poor lighting conditions where a hue’s vitality is lost.
    • Brightness can be measured as a percentage from 100% to 0%.
    • As the brightness of a fully saturated hue decreases, it appears progressively darker and achromatic.

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 is that it provides a more intuitive way than the RGB colour model to select and adjust colours in software applications used for graphic design, web development and photography.

Both RGB and HSB are additive colour models with red, green and blue primary colours. But whilst RGB relies on directly adjusting the amount of red, green and blue light needed to produce other colours the HSB colour model relies on adjusting hue, saturation and brightness.

  • Hue refers to the perceived difference between colours and is usually described using names such as red, yellow, green, or blue.
    • Hue can be measured as a location on an HSB colour wheel and expressed as a degree between 0 and 360.
  • Saturation refers to the vividness of a colour compared to an unsaturated colour.
    • Saturation is measured between a fully saturated colour (100%) and an unsaturated colour (0%)that appears either:
      • Dull and washed out until all colour disappears, leaving only a monochromatic grey tone (0%).
      • Misty or milky the nearer they are to white.
    • On many HSB colour wheels, saturation decreases from the edge to the centre.
  • Brightness refers to the perceived difference in the appearance of colours under ideal sunlit conditions compared to poor lighting conditions where a hue’s vitality is lost.
    • Brightness can be measured as a percentage from 100% to 0%.
    • As the brightness of a fully saturated hue decreases, it appears progressively darker and achromatic.
HSB colour model in practice

In the implementation of the HSB colour model used in Adobe Illustrator CC:

  • The HSB colour model can be accessed in the Colour Panel.
  • If the Colour Panel is not visible, find it in the Windows menu.
  • To switch from the default RGB setting to HSB, click on the hamburger menu (icon with three horizontal lines) in the top right of the panel.
  • Hue, saturation, and brightness can all be adjusted using the sliders or by clicking anywhere on the HSB Spectrum.
  • To enter an HSB colour using hexadecimal notation, switch back to the RGB colour model using the hamburger menu and enter the code in the provided window.
  • HSB notation typically appears as follows:
    • H = 00, S = 100%, B = 100% produce a fully saturated primary red hue with maximum brightness.
    • H = 00, S = 100%, B = 50% produce a fully saturated primary red hue that has lost some of its brightness so appears much darker in colour.
    • H = 00, S = 50%, B =  100% produce a bright but less saturated primary red hue.
Related diagrams

Each diagram below can be viewed on its own page with a full explanation.

References
  • 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 is that it provides a more intuitive way than the RGB colour model to select and adjust colours in software applications used for graphic design, web development and photography.
  • Both RGB and HSB are additive colour models with red, green and blue primary colours. But whilst RGB relies on directly adjusting the amount of red, green and blue light needed to produce other colours the HSB colour model relies on adjusting hue, saturation and brightness.
  • Hue refers to the perceived difference between colours and is usually described using names such as red, yellow, green, or blue.
    • Hue can be measured as a location on an HSB colour wheel and expressed as a degree between 0 and 360.
  • Saturation refers to the vividness of a colour compared to an unsaturated colour.
    • Saturation is measured between a fully saturated colour (100%) and an unsaturated colour (0%)that appears either:
      • Dull and washed out until all colour disappears, leaving only a monochromatic grey tone (0%).
      • Misty or milky the nearer they are to white.
    • On many HSB colour wheels, saturation decreases from the edge to the centre.
  • Brightness refers to the perceived difference in the appearance of colours under ideal sunlit conditions compared to poor lighting conditions where a hue’s vitality is lost.
    • Brightness can be measured as a percentage from 100% to 0%.
    • As the brightness of a fully saturated hue decreases, it appears progressively darker and achromatic.

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 hue, saturation, and brightness of a colour.
  • For example:
    • The HSB values for pure red are(0, 100%, 100%): Hue: 0°, Saturation: 100%, Brightness: 100%.
    • A lighter, pastel version of red might be (0, 50%, 100%): Hue: 0°, Saturation: 50%, Brightness: 100%.
    • A very dark, muted red could be: Hue (0, 100%, 20%): 0°, Saturation: 100%, Brightness: 20%.
  • The values assigned to the three parameters can be used to define millions of different colours.
  • Typically, the HSB colour model is implemented as follows:
    • Hue is represented in degrees from 0 to 360, corresponding to locations on the circumference of a colour wheel.
    • Saturation is represented as a percentage, where 100% denotes a fully saturated colour, and 0% denotes a fully desaturated colour.
    • Brightness is represented as a percentage, where 100% denotes the highest luminance of a colour, and 0% denotes the darkest possible shade of a 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 hue, saturation, and brightness of a colour.
  • For example:
    • The HSB values for pure red are(0, 100%, 100%): Hue: 0°, Saturation: 100%, Brightness: 100%.
    • A lighter, pastel version of red might be (0, 50%, 100%): Hue: 0°, Saturation: 50%, Brightness: 100%.
    • A very dark, muted red could be: Hue (0, 100%, 20%): 0°, Saturation: 100%, Brightness: 20%.
  • The values assigned to the three parameters can be used to define millions of different colours.
  • Typically, the HSB colour model is implemented as follows:
    • Hue is represented in degrees from 0 to 360, corresponding to locations on the circumference of a colour wheel.
    • Saturation is represented as a percentage, where 100% denotes a fully saturated colour, and 0% denotes a fully desaturated colour.
    • Brightness is represented as a percentage, where 100% denotes the highest luminance of a colour, and 0% denotes the darkest possible shade of a colour.
Related diagrams

Each diagram below can be viewed on its own page with a full explanation.

References

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 adjustments that can be made to hue, saturation and brightness to produce different colours.

  • The HSL and HSB are very similar models and are often used interchangeably. They both represent colours based on Hue, Saturation, and a third component.
  • In the HSB colour model brightness refers to the overall luminance of a colour.
  • In the HSB colour model, brightness represents the colour independent of adding white or black. It’s like a dimmer switch for the chosen colour.
  • In the HSL colour model, lightness refers to how light or dark a colour appears, considering how our eyes perceive brightness relative to a neutral grey. This is why a 50% light value represents a medium tone, even though it might not be the same brightness for all hues.
  • Both the HSB colour model and the HSL colour model are usually represented as a cylinder, where the hue is represented by an angle around the central axis, the saturation is represented as the distance from the central axis, and the brightness or lightness is represented as a distance along the vertical axis.
  • The difference between the two models lies in how the lightness and brightness components are calculated. In HSB, the brightness value is calculated by summing the highest and lowest RGB components and then dividing by two. In HSL, the lightness value is calculated by averaging the highest and lowest RGB components.
  • Both models are used to represent colours in a way that is more intuitive and user-friendly for adjustments compared to the RGB model.
  • Due to the similarity between HSB and HSL, they are often used interchangeably, and the difference in implementation is minor. Many software applications, including Adobe software, implement HSB (Hue, Saturation, Brightness) as a way to adjust colours easily and intuitively.

HSB colour model

HSL color solid cylinder saturation gray
HSL_color_solid_cylinder.png: SharkDderivative work: SharkD  Talk, CC BY-SA 3.0, via Wikimedia Commons

Related diagrams

Each diagram below can be viewed on its own page with a full explanation.

References
  • 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 adjustments that can be made to hue, saturation and brightness to produce different colours.
  • The HSL and HSB are very similar models and are often used interchangeably. They both represent colours based on Hue, Saturation, and a third component.
  • In the HSB colour model brightness refers to the overall luminance of a colour.
  • In the HSB colour model, brightness represents the colour independent of adding white or black. It’s like a dimmer switch for the chosen colour.
  • In the HSL colour model, lightness refers to how light or dark a colour appears, considering how our eyes perceive brightness relative to a neutral grey. This is why a 50% light value represents a medium tone, even though it might not be the same brightness for all hues.
  • Both the HSB colour model and the HSL colour model are usually represented as a cylinder, where the hue is represented by an angle around the central axis, the saturation is represented as the distance from the central axis, and the brightness or lightness is represented as a distance along the vertical axis.

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 adjustments that can be made to hue, saturation and brightness to produce different colours.

  • The HSL and HSB are very similar models and are often used interchangeably. They both represent colours based on Hue, Saturation, and a third component.
  • In the HSB colour model brightness refers to the overall luminance of a colour.
  • In the HSB colour model, brightness represents the colour independent of adding white or black. It’s like a dimmer switch for the chosen colour.
  • In the HSL colour model, lightness refers to how light or dark a colour appears, considering how our eyes perceive brightness relative to a neutral grey. This is why a 50% light value represents a medium tone, even though it might not be the same brightness for all hues.
  • Both the HSB colour model and the HSL colour model are usually represented as a cylinder, where the hue is represented by an angle around the central axis, the saturation is represented as the distance from the central axis, and the brightness or lightness is represented as a distance along the vertical axis.
  • The difference between the two models lies in how the lightness and brightness components are calculated. In HSB, the brightness value is calculated by summing the highest and lowest RGB components and then dividing by two. In HSL, the lightness value is calculated by averaging the highest and lowest RGB components.

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 colour of an object or light source, and is determined by the dominant wavelength of light it emits or reflects.
  • Hue is often used to describe colours in terms of their position on the colour wheel. Colour wheels are circular diagrams that arrange colours according to their hue.
  • The most commonly used colour wheel is the RGB colour wheel, which includes primary colours of red, green and blue, as well as secondary and tertiary colours.
  • Hues can be warm or cool, depending on their position on the colour wheel. Warm hues are those that include red, orange and yellow, while cool hues include blue, green and purple.
  • The perceived brightness and saturation of a hue can be affected by its surrounding colours, as well as by lighting conditions.
  • The perception of hue is also influenced by cultural and personal associations, as well as context and other environmental factors.
  • In the fields of art, design and visual communication, a good understanding of hue is essential for creating effective and visually appealing colour schemes.
  • In digital imaging and colour reproduction, hue can be adjusted through techniques such as colour correction and colour grading, to achieve the desired colour balance and tone.
About the term hue here at lightcolourvision.org
  • At lightcolourvision.org, we use the term “hue” to refer to the attribute of a colour that distinguishes it from other colours on the colour spectrum.
  • Colour models analyse and describe colours and their attributes in various ways. Some are grounded in the way the human eye perceives colours, others provide mathematical explanations.
  • The RGB colour model is a widely used additive colour model that describes colours in terms of the amounts of red, green, and blue light that are combined to create the colour.
  • In the HSB colour model, hue is one of the three attributes that describe a colour, alongside saturation and brightness.
  • The HSB colour model is commonly used in digital design and is a popular way to describe colours on electronic devices like televisions, computers, and mobile phones.
  • The CMYK colour model is used in print and focuses on the colours created by mixing cyan, magenta, yellow, and black inks on paper. Because the CMYK model doesn’t explicitly use the term “hue,” it is not a primary concern when designing for print.
Related diagrams

Each diagram below can be viewed on its own page with a full explanation.

References
  • 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 colour of an object or light source, and is determined by the dominant wavelength of light it emits or reflects.
  • Hue is often used to describe colours in terms of their position on the colour wheel. Colour wheels are circular diagrams that arrange colours according to their hue.
  • The most commonly used colour wheel is the RGB colour wheel, which includes primary colours of red, green and blue, as well as secondary and tertiary colours.
  • Hues can be warm or cool, depending on their position on the colour wheel. Warm hues are those that include red, orange and yellow, while cool hues include blue, green and purple.
  • The perceived brightness and saturation of a hue can be affected by its surrounding colours, as well as by lighting conditions.
  • The perception of hue is also influenced by cultural and personal associations, as well as context and other environmental factors.

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 colour of an object or light source, and is determined by the dominant wavelength of light it emits or reflects.
  • Hue is often used to describe colours in terms of their position on the colour wheel. Colour wheels are circular diagrams that arrange colours according to their hue.
  • The most commonly used colour wheel is the RGB colour wheel, which includes primary colours (hues) of red, green and blue, as well as secondary and tertiary colours.
  • Hues can be warm or cool, depending on their position on the colour wheel. Warm hues are those that include red, orange and yellow, while cool hues include blue, green and purple.
  • The perceived brightness and saturation of a hue can be affected by its surrounding colours, as well as by lighting conditions.
  • The perception of hue is also influenced by cultural and personal associations, as well as context and other environmental factors.

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 the total brightness of the light source.

  • 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 the total brightness of the light source.
  • When a book is placed on a table, different levels of illuminance can be observed depending on whether the sky is overcast, the time of day, or whether the surface is indirectly lit.
  • Illuminance is a measure of the amount of light that falls on a surface per unit area. It is determined by the intensity of the light source and the distance from the light source to the surface, but is independent of the characteristics of the surface it strikes, such as its colour or reflectivity.

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 the total brightness of the light source.

  • When a book is placed on a table, different levels of illuminance can be observed depending on whether the sky is overcast, the time of day, or whether the surface is indirectly lit.
  • Illuminance is a measure of the amount of light that falls on a surface per unit area. It is determined by the intensity of the light source and the distance from the light source to the surface, but is independent of the characteristics of the surface it strikes, such as its colour or reflectivity.
  • Illuminance is a measure of the quantity of light that falls on a surface, but it does not provide information about the spectral composition or other characteristics of the light. Other measures such as spectral power distribution, colour temperature, and colour rendering index can be used to describe other qualities of light beyond illuminance.
  • The brightness of a light source does not necessarily correspond with its illuminance. For example, a 10-watt light bulb placed next to a person reading a book can provide enough illuminance, while a 1000-watt light bulb located far away may not provide enough light to read by.
  • Illuminance is typically measured in units of lux (lx).
Related diagrams

Each diagram below can be viewed on its own page with a full explanation.

References

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 physiological effect.
  • Illumination can be provided through artificial light sources such as lamps and light fixtures, or natural illumination by capturing daylight.
  • Daylighting, which involves the use of windows, skylights or light shelves, is sometimes used as the main source of light during daytime in buildings.
  • Specialized forms of artificial lighting have been developed to suit every possible situation and purpose where natural light is not available, such as in underground spaces or during nighttime.
  • The colour temperature of light can affect how colours appear to an observer. Lighting producing a colour temperature below 4000K produces the impression of warmer colours. Lighting producing a colour temperature above 5000K produces the impression of cooler colours.

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, or natural illumination by capturing daylight.
  • Daylighting, which involves the use of windows, skylights or light shelves, is sometimes used as the main source of light during daytime in buildings.
  • Specialized forms of artificial lighting have been developed to suit every possible situation and purpose where natural light is not available, such as in underground spaces or during nighttime.
  • The colour temperature of light can affect how colours appear to an observer. Lighting producing a colour temperature below 4000K produces the impression of warmer colours. Lighting producing a colour temperature above 5000K produces the impression of cooler colours.
  • Colour temperature is measured in Kelvin (K) – the lower the number, the warmer the white light appears, while a higher Kelvin will appear cooler. Colour temperature generally ranges from 2700-3300K (warm) to 3300-5300 (cool) – and 6500K is daylight.
Related diagrams

Each diagram below can be viewed on its own page with a full explanation.

References

Impact parameter

The term impact parameter refers to a scale used on a ray-tracing diagram to measure the point at which incident rays strike the surface of a raindrop. Rays are given a value between 0.0 and 1.0 depending upon their point of impact.

  • For a primary rainbow, all the incident rays of interest strike a raindrop between its horizontal axis (0.0 on the impact parameter scale) and the upper-most point (1.0 on the impact parameter scale). In the second case, the ray grazes the surface at 900 to the normal and continues on its course without deviation.
  • For a secondary rainbow, all the incident rays of interest strike a raindrop between its horizontal axis (0.0 on the impact parameter scale) and the lowest point (1.0 on the impact parameter scale). In the second case, the ray grazes the surface at 900 to the normal and continues on its course without deviation.
  • An impact parameter is useful because it allows the relationship between equidistant incident rays, the angle at which they strike the surface and their angle of refraction to be plotted.

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. These incandescent filaments emit radiation across a broad spectrum, including infrared (heat) and some ultraviolet radiation. Only a small portion of this radiation falls within the visible range, which is perceived as light.

  • Incandescent light is produced when electricity flows through a filament, typically made of tungsten, heating it to thousands of degrees Celsius. This intense heat excites the atoms in the filament, causing them to change their energy levels and behaviour:
Energy Levels and Electrons
  • Atoms have distinct energy levels where electrons reside. Imagine these levels like steps on a ladder. The lowest energy level, called the ground state, is like the bottom step. Excitation occurs when atoms absorb energy, such as heat, causing their electrons to jump to higher energy levels (like climbing the ladder).
Energy Absorption and Excitation
  • The heat energy that causes excitation comes in the form of electromagnetic radiation, at visible light or infrared wavelengths. When the radiation collides with atoms, they can transfer their energy to the electrons. If the transferred energy matches the difference between two energy levels in the atom, the electron absorbs it and “excites” to the higher level.
Instability and Return
  • An excited atom is unstable and wants to return to its ground state. It does this by releasing the absorbed energy in different ways:
    • Light Emission: In many cases, the excited atom releases the energy as a photon (light particle) with a specific wavelength corresponding to the energy difference between the initial and final levels. This is how processes like incandescent light, neon signs, and some types of lasers work.
    • Collisions between atoms: The excited atom can transfer its energy to another atom through a collision. This can cause a chain reaction or lead to other physical or chemical reactions.
Colour and Efficiency
  • The colour of incandescent light depends on the filament temperature. Hotter filaments emit more bluish light, while cooler ones glow yellow or orange. However, incandescent light sources are generally less efficient than other lighting technologies, converting a significant portion of their energy into heat rather than light.
Examples
  • Incandescent light: In a hot gas, like the filament in an incandescent bulb, heating excites atoms, causing them to emit visible light, producing their characteristic glow.
  • Fluorescent Light: In fluorescent lamps, UV radiation excites atoms in a gas, the excited atoms then transfer their energy to other atoms, which in turn emit visible light.
  • Aurora: When sunlight excites atoms in the atmosphere, it causes them to emit specific wavelengths of light, resulting in phenomena like the aurora borealis.
Applications and Decline
  • While largely replaced by more efficient options like LED bulbs, incandescent lighting is still used in some applications due to its familiar warm glow and dimming capabilities.
  • However, its use is declining due to its lower energy efficiency and shorter lifespan.
Related diagrams

Each diagram below can be viewed on its own page with a full explanation.

References

Summary

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 another surface, such as a mirror.
  • When incident light strikes a surface or object, it may be absorbed, reflected, refracted, transmitted or undergo any combination of these optical effects.
  • Incident light is typically represented on a ray diagram as a straight line with an arrow to indicate its direction of propagation.
  • A ray diagram is a diagram that uses lines and arrows to represent the path of light, and labels to indicate the angles, directions, and other optical properties of the light.
  • Incident light is an important concept in optics and is used in various fields, including photography, astronomy, and physics.
Related diagrams

Each diagram below can be viewed on its own page with a full explanation.

References

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 from the Sun, an artificial source or may have already been reflected off another surface, such as a mirror.
  • When incident light strikes a surface or object, it may be absorbed, reflected, refracted, transmitted or undergo any combination of these optical effects.
  • Incident light is typically represented on a ray diagram as a straight line with an arrow to indicate its direction of propagation.

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 vacuum.

  • Refractive index (or, index of refraction) is a measurement of how much the speed of light is reduced when it passes through a medium compared to the speed of light in a vacuum.
  • The concept of refractive index applies to the full electromagnetic spectrum, from gamma-rays to radio waves.
  • Refractive index can vary with the wavelength of the light being refracted. This phenomenon is called dispersion, and it is what causes white light to split into its constituent colours when it passes through a prism.
  • The refractive index of a material can be affected by various factors such as temperature, pressure, and density.
  • The refractive index of a medium is a numerical value and is represented by the symbol n.
  • Because it is a ratio of the speed of light in a vacuum to the speed of light in a medium there is no unit for refractive index.
  • The refractive index of water is 1.333, meaning that light travels at 2/3 the speed in water compared to a vacuum.
  • If the refractive index of a medium is 1.5, for example, light travels at 2/3 the speed through glass compared to a vacuum.
  • As light undergoes refraction, its wavelength changes, but its frequency remains the same.
  • As light undergoes refraction its frequency remains the same.
  • The energy transported by light is not affected by refraction or the refractive index of a medium, but the intensity of the light can be affected.
Related diagrams

Each diagram below can be viewed on its own page with a full explanation.

References

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 vacuum.

  • Refractive index (or, index of refraction) is a measurement of how much the speed of light is reduced when it passes through a medium compared to the speed of light in a vacuum.
  • The concept of refractive index applies to the full electromagnetic spectrum, from gamma-rays to radio waves.
  • The refractive index can vary with the wavelength of the light being refracted. This phenomenon is called dispersion, and it is what causes white light to split into its constituent colours when it passes through a prism.
  • The refractive index of a material can be affected by various factors such as temperature, pressure, and density.