Visible & UV light

• Different colours of light have different wavelengths. The red has the longest and violet has the shortest.
• Ultra violet radiation can be used in sun beds (artificial) and get a sun tan/burn (natural).
• Fluorescence happens when ultraviolet light is absorbed and the energy is re-emitted as visible light.
• Ultraviolet can be used in security, as markings are put on money and passports to show authenticity but it is only shown when we shine UV light on it.
• The colour of an object depends on;

  • The wavelengths hitting it
  • The properties of the object
  • This determines which waves are absorbed, reflected or transmitted.
• Opaque objects are those that don't transmit light, meaning they are either absorbed or reflected. They may also reflect a range of colours which combine together.

  For example, if something appears blue then it is reflecting the blue wavelength and absorbing all the rest.
• Transparent means that the object transmits all the light.
• Translucent objects transmit a proportion of light which determines how well we can see through them. The colour which is transmitted most will be the colour of the object.
• Colour filters - filters which absorb certain wavelengths and transmit others.