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 physics of the atom by introducing the concept of quantized energy levels for electrons.

  • While the Bohr model provided valuable insights into atomic structure and spectral lines, it had limitations, especially when applied to larger atoms. It was eventually superseded by quantum mechanics, which provided a more comprehensive understanding of the behaviour of electrons in atoms.

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 opposed to colour brightness) is used to refer to a property of light.
  • Colour brightness is used to refer to how much colour something appears to emit or reflect towards an observer.
  • Colour brightness can be understood as the variation in how a colour is perceived by an observer under well-lit conditions compared to its more muted appearance when in shadow or under poor illumination.
  • In the HSB colour model:
    • Hue refers to the perceived difference between colours and is usually described using names such as red, yellow, green, or blue.
    • Saturation refers to the vividness of a colour compared to an unsaturated colour.
    • 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.

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 opposed to colour brightness) is used to refer to a property of light.
  • Colour brightness is used to refer to how much colour something appears to emit or reflect towards an observer.
  • When brightness is used in connection with the HSB colour model it is used alongside hue and saturation and refers to the method of selecting and adjusting colours in software applications such as Adobe Illustrator.
  • The HSB colour model is a representation of colours that combines hue, saturation, and brightness components.
  • In the HSB brightness represents the intensity or lightness of a colour, with higher values indicating brighter or lighter colours.

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 of factors such as angle of incidence, wavelength, frequency, or amplitude.
  • A perfect blackbody doesn’t exist in reality. However, certain objects and materials, such as stars and carbon in soot or graphite behave almost like blackbodies.
  • When a blackbody emits electromagnetic radiation, the spectral distribution of the emissions is dependent solely on its temperature.
  • The radiation emitted by a black body is known as blackbody radiation.
  • If enough heat is applied to a blackbody, it will begin to appear orange at a certain point, and as the temperature increases, it changes from white to pale blue and then to light blue.

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 cells, they connect to amacrine cells that assist in integrating information and forming a comprehensive picture of an entire visual scene.
  • There are approximately a dozen types of bipolar cells, all of which serve as centres for integration.
  • Each type of bipolar cell acts as a dedicated channel for information about light, collected by either a single or a small group of rod or cone cells.
  • Each type of bipolar cell interprets and relays its own version of information gathered from photoreceptors to ganglion cells

Bipolar cells

Bipolar cells

Bipolar cells, a type of neuron found in the retina of the human eye connect with other types of nerve cells via synapses. They act, directly or indirectly, as conduits through which to transmit signals from photoreceptors (rods and cones) to ganglion cells.

There are around 12 types of bipolar cells and each one functions as an integrating centre for a different parsing of information extracted from the photoreceptors. So, each type transmits a different analysis and interpretation of the information it has gathered.

The output of bipolar cells onto ganglion cells includes both the direct response of the bipolar cell to signals derived from photo-transduction but also responses to those signals received indirectly from information provided by nearby amacrine cells that are also wired into the circuitry.

We might imagine one type of bipolar cell connecting directly from a cone to a ganglion cell that simply compares signals based on differences in wavelength. The ganglion cell might then use the information to determine whether a certain point is a scene is red or green.

Not all bipolar cells synapse directly with a single ganglion cell. Some channel information that is sampled by different sets of ganglion cells. Others terminate elsewhere within the complex lattices of interconnections within the retina so enabling them to carry packets of information to an array of different locations and cell types.

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 into colour.
  • When sunlight is dispersed by rain and forms a rainbow, an observer will typically distinguish red, orange, yellow, green, blue and violet bands of colour.
  • Although a rainbow contains electromagnetic waves with all possible wavelengths between red and violet, some ranges of wavelengths appear more intense to a human observer than others.