Seeing coloured objects
Physics Narrative for 11-14
Colour depends on the light source and the object
Why does a red dress appear red in ordinary white light?
When white light lands on a red dress some frequencies are absorbed and some frequencies are reflected. Those reflected are the correct combination for you to record
red, as this reflected light enters your eye and allows you to see the dress.
It is the red pigment or dye in the dress which controls this process of selective absorption and reflection.
You may have had the experience, whilst shopping, of being advised to look at some item of clothing outside in the daylight to see what it
really looks like. This reminds us that the colour of an object not only depends on the colouring pigments, but also on the ambient light in which it is being viewed.
You might use red, green or blue torches to illuminate the vase:
We usually assume that the
normal colour of an object is how it appears in white light. If the ambient light is not white the object will appear a different colour.