Engaging questions:

  • What do we see on the back of CD/DVD when we illuminate it with flashlight?
  • When can we see a rainbow?
  • What is the colour of the sunlight?
  • How many colours are there in the rainbow?
  • What is the colour of the sky?
  • Why sky is blue during a day and yellow or red in the evening?
  • Why stars are invisible during a day?
  • Why is the sky blue during a day, the evening?


  • a cardboard or PCV tube of the length of about 50 cm,
  • carton – for aperture preparation,
  • plasticine – as a sealant,
  • a lamp with bulb or a flashlight,
  • splitting element e.g.  diffraction grating, prism or CD/DVD (from the recorded disc, the layer of an aluminium foil should be removed, e.g. by sticking and unsticking the adhesive tape),
  • recorder – digital photo camera (the mobile phone camera may be used).

Description of the Activity :

The spectroscope diagram is presented at Figure II.1. One side of the tube should be shut off by the aperture (a cardboard disk with a slit as narrow as possible). The disk can be embedded and sealed with the use of plasticine. On the other side of the tube (about 3-4 cm from the end), a transverse incision should be made, being a place for the splitting element, which should be put there. The light source should be placed on the side with the slit.  On the other side, at an angle of about 30 degrees, a  light detector should be placed (Figure II.1).  In order to prevent light entering the detector from the side, it can be covered with a cloth. The spectrum of the bulb and of the sun are recorded.

Figure II.1. A diagram of the spectrometer structure.


  • Are the observed light colours similar to the rainbow?
  • Are the colours of the rainbow arranged in the specific order?
  • Are the observed light colours similar to the colours of the sky?
  • Why is the light being split?
  • What parameter influences the level of colour separation?

Figure II.2. An exemplary bulb light spectrum a) splitting element – a diffraction grating, b) splitting element – a CD