Lateral geniculate nucleus

The lateral geniculate nucleus is a relay centre on the visual pathway from the eyeball to the human brain. It receives a major sensory input from the retina via the axons of ganglion cells.

  • The thalamus which houses the lateral geniculate nucleus is a small structure within the brain, located just above the brain stem between the cerebral cortex and the midbrain and has extensive nerve connections to both.
  • The lateral geniculate nucleus is the central connection for the optic nerve to the occipital lobe, particularly the primary visual cortex.
  • Both the left and right hemispheres of the brain have a lateral geniculate nucleus.
  • There are three major cell types in the lateral geniculate nucleus which connect to three distinct types of ganglion cells:
    • P ganglion cells send axons to the parvocellular layer of the lateral geniculate nucleus.
    • M ganglion cells send axons to the magnocellular layer.
    • K ganglion cells send axons to a koniocellular layer.
  • The lateral geniculate nucleus specialises in calculations based on the information it receives from both the eyes and from the brain. Calculations include resolving temporal and spatial correlations between different inputs. This means that things can be organised in terms of the sequence of events over time and the relationship of things within the overall field of view.
  • Some of the correlations deal with signals received from one eye or the other. Some deal with the left and right semi-fields of view captured by both eyes. As a result, they help to produce a three-dimensional representation of the field of view of an observer.
  • Other important factors to note regarding the lateral geniculate nucleus are:
    • The lateral geniculate nucleus carries out many functions, some are directed towards the eyes, others are directed towards the brain.
    • A signal is provided to control the vergence of the two eyes so they converge at the principal plane of interest in object-space at any particular moment.
    • A signal is provided to control the focus of the eyes based on the calculated distance to the principal plane of interest.
    • Computations are achieved to determine the position of every major element in object-space relative to the principal plane. Through subsequent motion of the eyes, a larger stereoscopic mapping of the visual field is achieved.
    • A tag is provided for each major element in the central field of view of object-space. The accumulated tags are attached to the features in the merged visual fields and are forwarded to the primary visual cortex.
    • A tag is provided for each major element in the visual field describing the velocity of the major elements based on changes in position over time. The velocity tags (particularly those associated with the peripheral field of view) are also used to determine the direction the organism is moving relative to object-space.

https://en.wikipedia.org/wiki/Lateral_geniculate_nucleus

Law of refraction (Snell’s Law)

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 with reference to the refractive indices of both media as follows:

When electromagnetic radiation (light) of a specific frequency crosses the interface of any given pair of media, the ratio of the sines of the angles of incidence and the sines of the angles of refraction is a constant in every case.

  • Snell’s law deals with the fact that for an incident ray approaching the boundary of two media, the sine of the angle of incidence multiplied by the index of refraction of the first medium is equal to the sine of the angle of refraction multiplied by the index of refraction of the second medium.
  • Snell’s law deals with the fact that the sine of the angle of incidence to the sine of the angle of refraction is constant when a light ray passes across the boundary from one medium to another.
  • Snell’s law can be used to calculate the angle of incidence or refraction associated with the use of lenses, prisms and other everyday materials.
  • When using Snell’s law:
    • The angles of incidence and refraction are measured between the direction of a ray of light and the normal – where the normal is an imaginary line drawn on a ray diagram perpendicular to, so at a right angle to (900), to the boundary between two media.
    • The wavelength of the incident light is accounted for.
    • The refractive indices used are selected for the pair of media concerned.
    • The speed of light is expressed in metres per second (m/s).

Law of refraction (Snell’s law)

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 with reference to the refractive indices of both media as follows:

When electromagnetic radiation (light) of a specific frequency crosses the interface of any given pair of media, the ratio of the sines of the angles of incidence and the sines of the angles of refraction is a constant in every case.

  • Snell’s law deals with the fact that for an incident ray approaching the boundary of two media, the sine of the angle of incidence multiplied by the index of refraction of the first medium is equal to the sine of the angle of refraction multiplied by the index of refraction of the second medium.
  • Snell’s law deals with the fact that the sine of the angle of incidence to the sine of the angle of refraction is constant when a light ray passes across the boundary from one medium to another.
  • Snell’s law can be used to calculate the angle of incidence or refraction associated with the use of lenses, prisms and other everyday materials.
  • When using Snell’s law:
    • The angles of incidence and refraction are measured between the direction of a ray of light and the normal – where the normal is an imaginary line drawn on a ray diagram perpendicular to, so at a right angle to (900), to the boundary between two media.
    • The wavelength of the incident light is accounted for.
    • The refractive indices used are selected for the pair of media concerned.
    • The speed of light is expressed in metres per second (m/s).

https://en.wikipedia.org/wiki/Snell%27s_law

LED

An LED (Light-emitting-diode) is an electroluminescent light source. It produces light by passing an electrical charge across the junction of a semiconductor.

Multi-colour LED’s typically contain three separate diodes that mix red, green and blue wavelengths to produce a full range of colours.

  • LED’s don’t produce white light in the same way that incandescent lamps do.
  • One LED cannot produce the full range of colours that sunlight or incandescent light produces.
  • A LED typically emits a single colour of light which is composed of a very narrow range of wavelengths.
  • However LED’s emitting the three primary colours of red, green and blue light can be combined to produce white light.
  • By changing the relative intensity of the primary colours, a multi-colour LED produces an extremely wide range of colours.
  • An LED light source is often used to demonstrate the effect of projecting primary coloured lights onto a dark surface because they emit light in very narrow bands of wavelengths. The peak wavelength for the selected lights might typically be red = 625 nanometres, green = 500 nm, blue = 440 nm.

https://en.wikipedia.org/wiki/Light-emitting_diode

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, electromagnetic radiation would have been emitted by stars since the formation of the first galaxies over 13 billion years ago.

  • Simply stated, light is energy. Light is the way energy travels through space.
  • Light and colour are entirely different phenomena. Whilst light is electromagnetic radiation, the experience of colour is a feature of human vision that depends first of all on the construction of our eyes and the wavelength, frequency and amplitude of visible light that strikes the retina.
  • The human eye, and so human perception, is tuned to the visible spectrum and so to spectral colours between red and violet. It is the sensitivity of the eye to this small part of the electromagnetic spectrum that results in the perception of colour.
  • Whilst the term light can be used to refer to the whole of the electromagnetic spectrum, visible light refers to the small range of wavelengths that our eyes are tuned to.
  • The term light can be used in three different ways:
  • Light can be used to mean the whole of the electromagnetic spectrum from radio waves, through visible light to gamma rays. When this meaning is intended, the terms radiant energy or photon energy are placed in brackets after the term light in this resource.
  • Light can be used to mean the range of wavelengths and frequencies that can be detected by the human eye. A better term is visible light which refers to the wavelengths that correspond with the colours between red and violet, the visible spectrum.
  • Light can also be used to mean the range of wavelengths and frequencies between infra-red and ultra-violet. This usage is sometimes useful because the outer limits of the visible spectrum can differ under different lighting conditions and for different individuals.

https://en.wikipedia.org/wiki/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, electromagnetic radiation would have been emitted by stars since the formation of the first galaxies over 13 billion years ago.

  • Simply stated, light is energy. Light is the way energy travels through space.
  • Whilst the term light can be used to refer to the whole of the electromagnetic spectrum, visible light refers to the small range of wavelengths that our eyes are tuned to.
  • The term light can be used in three different ways:
  • Light can be used to mean the whole of the electromagnetic spectrum from radio waves, through visible light to gamma rays. When this meaning is intended, the terms radiant energy or photon energy are placed in brackets after the term light in this resource.
  • Light can be used to mean the range of wavelengths and frequencies that can be detected by the human eye. A better term is visible light which refers to the wavelengths that correspond with the colours between red and violet, the visible spectrum.
  • Light can also be used to mean the range of wavelengths and frequencies between infra-red and ultra-violet. This usage is sometimes useful because the outer limits of the visible spectrum can differ under different lighting conditions and for different individuals.

Light source

A light source is a natural or man-made object that emits one or more of wavelengths of light.

  • The Sun is the most important light source in our lives and emits every wavelength of light in the visible spectrum.
  • Celestial sources of light include other stars, comets and meteors.
  • Other natural sources of light include lightning, volcanoes and forest fires.
  • There are also bio-luminescent light sources including some species of fish and insects as well as types of bacteria and algae.
  • Man-made light sources of the most simple type include natural tars and resins, wax candles, lamps that burn oil, fats or paraffin and gas lamps.
  • Modern man-made light sources include tungsten light sources. These are a type of incandescent source which means they radiate light when electricity is used to heat a filament inside a glass bulb.
  • Halogen bulbs are more efficient and long-lasting versions of incandescent tungsten lamps and produce a very uniform bright light throughout the bulb’s lifetime.
  • Fluorescent lights are non-incandescent sources of light. They generally work by passing electricity through a glass tube of gas such as mercury, neon, argon or xenon instead of a filament. These lamps are very efficient at emitting visible light, produce less waste heat, and typically last much longer than incandescent lamps.
  • An LED (Light Emitting Diode) is an electroluminescent light source. It produces light by passing an electrical charge across the junction of a semiconductor.
  • Made-made lights can emit a single wavelength, bands of wavelengths or combinations of wavelengths.
  • An LED light typically emits a single colour of light which is composed of a very narrow range of wavelengths.

https://en.wikipedia.org/wiki/Light#Light_sources

Light source

A light source is a natural or man-made object that emits one or more of wavelengths of light.

  • The Sun is the most important light source in our lives and emits every wavelength of light in the visible spectrum.
  • Celestial sources of light include other stars, comets and meteors.
  • Other natural sources of light include lightning, volcanoes and forest fires.
  • There are also bio-luminescent light sources including some species of fish and insects as well as types of bacteria and algae.
  • Man-made light sources of the most simple type include natural tars and resins, wax candles, lamps that burn oil, fats or paraffin and gas lamps.
  • Modern man-made light sources include tungsten light sources. These are a type of incandescent source which means they radiate light when electricity is used to heat a filament inside a glass bulb.
  • Halogen bulbs are more efficient and long-lasting versions of incandescent tungsten lamps and produce a very uniform bright light throughout the bulb’s lifetime.
  • Fluorescent lights are non-incandescent sources of light. They generally work by passing electricity through a glass tube of gas such as mercury, neon, argon or xenon instead of a filament. These lamps are very efficient at emitting visible light, produce less waste heat, and typically last much longer than incandescent lamps.
  • An LED (Light Emitting Diode) is an electroluminescent light source. It produces light by passing an electrical charge across the junction of a semiconductor.
  • Made-made lights can emit a single wavelength, bands of wavelengths or combinations of wavelengths.
  • An LED light typically emits a single colour of light which is composed of a very narrow range of wavelengths.

Light stimulus

Light reaching the human eye is called a light stimulus because it stimulates the visual system.

  • Sometimes the term colour stimulus is used because the light stimulus produces the experience of colour for an observer. Every light stimulus can be described in terms of the composition and intensity of wavelengths of light that enter the eye.
  • Imagine, that at a specific moment, the wavelengths of a stimulus include reds, oranges, yellows, greens, blues and violets. The colour an observer sees depends on the response not only to the mixture of wavelengths that correspond with these colours but also to the intensity of the light at each wavelength.
  • In many situations, intensity varies progressively across a range of wavelengths and can be described by the spectral power distribution of the stimulus.

Luminance

The term luminance is used when talking about how illuminated objects appear to an observer.

  • Luminance is a measure of the intensity of light that reaches the eye.
  • So we can talk about:
    • The luminance desert sand under moonlight.
    • The luminance of a road surface under street lights.
    • The luminance of a book cover in sunshine.
  • Luminance can be measured and so is an objective term rather than a subjective experience.
  • The light produced by a table lamp can be described in terms of luminosity, the amount of light that is then reflected from a surface towards an observer can then be measured in terms of luminance.

https://en.wikipedia.org/wiki/Luminance

Luminosity

Luminosity is about light given off by a source such as the Sun or a light-bulb.

  • If one light bulb produces one unit of light, then two produces twice the luminosity and so on.
  • Because luminosity is about light being given off in all directions it is not something that an observer can see directly.
  • A light source’s luminosity depends on how much power it consumes. In the case of a light bulb, for example, it relates to the amount of electrical energy the bulb is burning and how much of that energy is being turned into visible light.
  • Luminosity is something that can be measured and so is an objective term.

 

  • If you have read about trichromatic vision, you will know that it is possible to match all the colours in the visible spectrum seen by an observer by appropriate mixing of wavelengths and intensities (luminosity) of light corresponding with three primary colours and this can be achieved without any loss of information so far as an observer is concerned.
  • Now imagine three light sources with wavelengths corresponding with red, green and blue connected to sliders that allows the luminosity of each component to be adjusted between a minimum of 0% (off) and a maximum of 100% (fully on).
  • Zero luminosity for each component means no light, so an observer in a windowless room would be in darkness. If each component is set to full luminosity our observer will see white. The exact quality of white depends on the type of lights, how accurately their wavelength is controlled and the surface the light falls upon.
  • If the sliders that control each light are set to the same value (and so to the same luminosity) between 1% and 99% then the result is a shade of grey, which appears darker as the intensity decreases or brighter as the intensity increases.
  • When the luminosity of each slider is set to different values, the result is the perception of a colour.
  • When one of the components has the highest luminosity, the colour will be a hue near that primary colour and so appear more reddish, greenish or bluish. When two components have the same high luminosity, then the observer sees the hue of a secondary colour (a shade of cyan, magenta or yellow).
  • Maximum luminosity of a spectral colour corresponds with its lightest tint.

 

  • Maximum luminosity of a display device corresponds with the brightest white it can reproduce and is called the white point.
  • The black point corresponds with the minimum luminosity of a device, so corresponds with the device being turned off.
  • The contrast ratio of maximum and minimum luminosity of a television or computer screen is typically more than 280:1

https://en.wikipedia.org/wiki/Adobe_RGB_color_space