Many students have an understanding of how coloured filters work, some believe they change the nature of the light in some way

Light, Sound and Waves


For example, a red filter 'dyes' the white light, or white light is given and carries the colour of the filter.

Resources to Address This

  • Colour separation with light filters  (11-14)

    Ref - SPT Li04 PN03

    An easier way to separate out light of different colours is to use coloured filters. For example, when white light passes through a pure red filter all of the other colours in the spectrum are absorbed and only red light passes through it. So only a very narrow band of frequencies get through.

    View Resource
  • Understanding colours  (11-16)

    Ref- Practical Physics; Light and optics; Spectra and colour;

    Ask students how the filters make light coloured. Does the red dye change all parts of the spectrum to red, or does it just cut out other colours and leave the red that was always there in the white light? Is the dye a colour adder or a colour subtractor? Filters transmit their own colour and absorb the rest. They do not dye all the light with their own colour. They subtract colour.

    View Resource


The following studies have documented this misconception:

  • Andersson, B. and Kärrqvist, C. () How Swedish pupils, aged 12‐15 years, understand light and its properties. European Journal of Science Education, 5 (4),


    DOI: 10.1080/0140528830050403.

    Review sheet

Limit Less Campaign

Support our manifesto for change

The IOP wants to support young people to fulfil their potential by doing physics. Please sign the manifesto today so that we can show our politicians there is widespread support for improving equity and inclusion across the education sector.

Sign today