A human observer is a person who engages in observation by watching things.

  • In the presence of visible light, an observer perceives colour because the retina at the back of the human eye is sensitive to wavelengths of light that fall within the visible part of the electromagnetic spectrum.
  • The visual experience of colour is associated with words such as red, blue, yellow, etc.
  • The retina’s response to visible light can be fully described in terms of wavelength, frequency and brightness.
  • Other properties of the world around us must be inferred from patterns of light.
The human retina
  • The perception of colour is a very subjective experience.
  • One factor that determines the particular colour an observer sees is the colour of nearby objects.
  • Another factor is to do with the well-being of an observer. Health, medications, mood, emotions or fatigue can all affect the eye, vision and perception.
  • A further factor is the environment in which colours are observed, the type of object and colour associations.
  • Two different observers may see colour differently because of their different life-experience including educational, social and cultural factors.
  • The term observer has distinct and different meanings within the fields of special relativity, general relativity, quantum mechanics, thermodynamics and information theory.