visible light

• visible light is made up of...

  a range of colours
• visible light spectrum


  red, orange, yellow, green, blue, indigo, violet
• each colour has its own...

  narrow range of wavelengths/frequencies
• red wavelength


  700 nm
• violet wavelength


  400 nm
• different mixture of these colours allow us to see...

  even more shades of colours
• when all of the colours are put together...

  white light is created
• white light

  mixture of all the colours in the visible spectrum
• different objects ... different wavelengths of light in different ways

  absorb, transmit and reflect
• opaque objects


  transmit no light (we cannot see through them). when visible light hits them, they absorb some wavelengths of light and reflect others
• the colour of an opaque object depends on...

  which wavelengths of light are most strongly reflected
• why does a red apple appear to be red?

  because the wavelengths corresponding to the red part of the visible spectrum are most strongly reflected, while other wavelengths are absorbed
• for opaque objects that are not a primary colour...

  they may be reflecting either the wavelengths of the light corresponding to that colour OR the wavelengths of the primary colours than can mix to make that colour
• why do white objects appear white?

  they reflect all of the wavelengths of visible light equally
• white is seen as...

  the presence of all visible light (i.e. the presence of all colour)
• why do black objects appear black?

  they absorb all wavelengths of visible light
• black is seen as...

  the lack of any visible light (i.e. the lack of any colour)
• transparent and translucent objects

  transmit some light (they are partially see through) and some is absorbed/reflected
• a transparent object's colour is related to...

  the wavelengths of light transmitted and reflected by it
• colour filters only let through...

  particular wavelengths
• what are colour filters used for?

  to filter out different wavelengths of light, so that only certain colours are transmitted and the rest are absorbed
• colour filter diagram

  
• if you look at a blue object through a blue colour filter...

  the object will appear blue, because blue light is transmitted by the filter
• if you look at a red object through blue colour filter...

  the object will appear black, because red light is not transmitted by the filter
• filters that aren't for primary colours let through...

  both the wavelengths of light for that colour AND the wavelengths of the primary colours that can be added together to make that colour