Absorption, reflection and transmission of visible light

Within the visible light range of the electromagnetic spectrum, there is a spectrum of colour. This is a continuous range of colours. In order of increasing frequency (and decreasing wavelength) these are given as:

  • red
  • orange
  • yellow
  • green
  • blue
  • indigo
  • violet

Each colour within the visible light spectrum has its own narrow band of wavelength and frequency.

Absorption of light

Waves can be absorbed at the boundary between two different materials. When waves are absorbed by a surface, the energy of the wave is transferred to the particles in the surface. This will usually increase the internal energy of the particles.

When white light shines on an opaque object, some wavelengths or colours of light are absorbed. These wavelengths are not detected by our eyes. The other wavelengths are reflected, and these are detected by our eyes.

For example, grass appears green in white light:

  • red, orange, yellow, blue, indigo and violet are absorbed by the grass
  • green light is reflected by the grass and detected by our eyes
A green sphere - with all the colours in the spectrum hitting the object. Three green arrows extent out of the object - this represents the green light being reflected.

Transmission of light

Waves can also be transmitted at the boundary between two different materials. When waves are transmitted, they continues through the material. Air, glass and water are common materials that are very good at transmitting light. They are transparent because light is transmitted with very little absorption. Translucent materials transmit some light but are not completely clear. Lamp shades, shower curtains and window blinds are often translucent objects.

Colour filters

When white light passes through a coloured filter, all colours are absorbed except for the colour of the filter. For example, an orange filter transmits orange light but absorbs all the other colours. If white light is shone on an orange filter, only the orange wavelengths will be observed by the human eye.

Seven coloured arrows, representing the spectrum of white light hitting an orange filter. On the other side of the filter only an orange arrow extends out.

Coloured objects in coloured light

An object appears to be black if it absorbs all the wavelengths of visible light. For example, an object that appears blue in white light will appear black in red light. This is because the red light contains no blue light for the object to reflect.