Colour & light

• Colour & Light

  • White light is a mixture of all the colours of the spectrum
  • Each colour has a different wavelength (and frequency), making up a very narrow part of the electromagnetic spectrum
  • White light may be separated into all its colours by passing it through a prism
  • This is done by refraction
  • Violet light is refracted the most, whilst red light is refracted the least
  • This splits up the colours to form a spectrum
• Colours from white light:

  A) White

  B) Spectrum

  
• Differential Absorption of Colour

  • Absorption occurs when: Energy is transferred from the wave into the particles of a substance
  • Waves can be partially or completely absorbed
  • Sound waves are absorbed by brick or concrete in houses
  • Light will be absorbed if the frequency of light matches the energy levels of the electrons
  • The light will be absorbed, and then reemitted over time as heat
  • If an object appears red, this means:
  • Only red light has been reflected
  • All the other frequencies of visible light have been absorbed
• Transmission & Absorption – Colour Filters

  • Colour filters work by absorbing certain wavelengths and transmitting other wavelengths
  • These certain wavelengths correspond to certain colours
  • When white light passes through a coloured filter, some colours are absorbed whilst others are able to pass straight through
  • For example, when white light passes through a red filter:
  • Red light is transmitted
  • All the other colours are absorbed
  • The colour that is transmitted is the same colour as the filter
• Reflection

  • The colour of an opaque object is determined by which wavelengths of light are more strongly reflected
  • Wavelengths that are not reflected are absorbed
  • Hence, this is why different objects appear to be different colours
  • For example, white light upon a green surface will only have green light reflected and the others absorbed
  • This light is reflected into our eyes to see the surface in that colour
• • An object will appear white if:
  • All wavelengths are reflected equally
  • An object will appear black if:
  • All wavelengths are absorbed
  • An object will appear transparent if:
  • All the light is transmitted, and only a small amount is reflected or absorbed
• Specular Reflection

  • Specular reflection is defined as: Reflection from a smooth surface in a single direction
  • When light reflects off a smooth surface, such as a mirror, specular reflection occurs
  • This is what gives a mirror its shiny appearance
• Scattering

  • Scattering is defined as:
  • Reflection from a rough surface in many directions
  • When light reflects off a rough surface, which applies to the majority of surfaces, diffuse reflection occurs
  • This is what gives objects a dull or matt appearance
  • This is why a reflection cannot be seen clearly from a table surface, for example
  • Even though a table's surface may look smooth from afar, it is actually made up of many tiny ridges which the light rays are scattered off
  • When light scatters, it leaves the surface in all directions