Dictionary tag: D

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 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, each wavelength of light encounters bumps and ridges exceeding their size.
  • Instead of reflecting neatly in one direction, the light scatters in different directions.
  • In this case, scattering doesn’t happen completely randomly. The surface features influence the direction of the scattered light, depending on the angle of incidence and the specific bumps and ridges it encounters.
  • This scattering creates diffuse reflections, responsible for the soft, uniform illumination seen on textured surfaces like matte paint or unpolished wood.
  • In the case of a matte phone screen, for example, the light doesn’t form a clear reflection of your face but rather creates a soft, hazy glow due to the diffused light.

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 the RGB (red, green, blue) colour model to represent and display information.
  • The range of colours that different types of screens can display depends on their technology and specifications.
  • Many RGB digital screens include light-emitting diodes (LEDs) that can directly or indirectly adjust the intensity of red, green and blue light within each addressable component of the screen to produce pixels of colour that together produce an image.
  • LEDs are typically used to backlight LCD (liquid crystal display )screens.  Different colours are created by colour filters and by adjusting the amount and the polarization of light that is allowed to pass through the crystal sub-pixels that make up each pixel on the screen.
  • In an OLED display, each pixel provides its own illumination. The organic materials in the OLED emit light when an electric current is applied. Because each pixel can be turned on or off individually, OLED displays can achieve deeper blacks (by completely turning off pixels) and a higher contrast ratio compared to LED-backlit LCD screens.

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 typically overlay highly reflective white paper with cyan, magenta, yellow and black inks or toner.
  • CMYK is a subtractive colour model suited to working with semi-transparent inks.
  • Printing has a smaller gamut than TV, computer and phone screens which rely on light emission, rather than reflection of light off sheets of paper.
  • Digital screens produce comparatively brighter colours than printers because the amplitude of each wavelength of light is larger than can be achieved by a printer.
  • Digital printers produce dull and less intense colours than digital screens because the amplitude of each wavelength of light is smaller when light is reflected off paper through inks.

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, each wavelength of light encounters bumps and ridges exceeding their size.
  • Instead of reflecting neatly in one direction, the light scatters in different directions.
  • In this case, scattering doesn’t happen completely randomly. The surface features influence the direction of the scattered light, depending on the angle of incidence and the specific bumps and ridges it encounters.
  • This scattering creates diffuse reflections, responsible for the soft, uniform illumination seen on textured surfaces like matte paint or unpolished wood.
  • In the case of a matte phone screen, for example, the light doesn’t form a clear reflection of your face but rather creates a soft, hazy glow due to the scattered light.

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 associated with all kinds of waves. Electromagnetic waves are a special case however because of their unique behaviour.
  • Diffraction of electromagnetic waves deals with the way light bends around the edges of obstacles into regions that would otherwise be in shadow.
  • Interference deals with the way that electromagnetic waves behave during the diffraction process.
  • Diffraction can be produced by the edges or by a hole (aperture) in any opaque surface or object.
  • Diffraction causes a propagating electromagnetic wave to produce a distinctive pattern as waves interfere with one another. The resulting pattern becomes visible if diffracted light subsequently strikes a surface.

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 with each wavelength to become visible to a human observer.

  • Chromatic dispersion refers to the dispersion of light according to its wavelength or colour.
  • Chromatic dispersion is the result of the relationship between wavelength and refractive index.
  • When light travels from one medium (such as air) to another (such as glass or water) each wavelength is refracted differently, causing the separation of white light into its constituent colours.
  • When light undergoes refraction each wavelength changes direction by a different amount. In the case of white light, the separate wavelengths fan out into distinct bands of colour with red on one side and violet on the other.
  • Familiar examples of chromatic dispersion are when white light strikes a prism or raindrops and a rainbow of colours becomes visible to an observer.