Vision

About light, colour & vision

Light

• The human eye and human vision are adapted and responsive to the visible spectrum, which includes wavelengths of light corresponding to colours ranging from red to violet..
• Light is the electromagnetic radiation that enables us to perceive colour. It consists of a spectrum of wavelengths, and it is the interaction of these wavelengths with our visual system that gives rise to the perception of different colours.
• The visible spectrum is the range of wavelengths of light that the human eye can detect, typically spanning from approximately 400 nanometers (nm) for violet to 700 nm for red.
• Light is seldom composed of a single wavelength, so an observer is typically exposed to a range of diverse wavelengths or a combination of wavelengths from various parts of the visible spectrum.
• Visible light does not possess any properties that set it apart from other segments of the electromagnetic spectrum.

Colour

• Colour is not an inherent property of electromagnetic radiation but rather a characteristic of vision and the visual perception of an observer.
• Colour is not an inherent property of electromagnetic radiation but rather a characteristic of vision and the visual perceptions of an observer.
• Colour is what human beings perceive when light is present.
• Objects appear to have different colours to an observer based on the wavelengths and intensity of light when it reaches the retina at the back of the eye.

Vision

• When light enters the eye, it interacts with specialized cells called cones in the retina. Cones are responsible for detecting and processing different wavelengths of light, which contribute to our perception of colour.
• The three types of cones, commonly referred to as red, green, and blue cones, respond to different ranges of wavelengths. The combined activity of these cones allows us to perceive a wide range of colours.
• The brain plays a crucial role in the perception of colour. It processes the signals received from the cones and interprets them to create our conscious experience of colour.
• Colour perception is influenced by various factors, including the intensity and quality of light, the surrounding environment, and individual differences in vision.
• Our ability to perceive and differentiate colours provides important cues about the world around us, helping us recognize objects, navigate our environment, and experience the richness of visual stimuli.

About trichromatic colour vision (Trichromacy)

Trichromatic colour theory explains how the human eye perceives colour.

• Trichromatic colour theory is based on the existence of three types of light-sensitive cone cells in the retina, each responsive to a different range of colours.
• The colours we perceive result from the combined responses of all three types of cones.
• The sensitivity of cone cells forms the physiological basis for trichromatic colour vision in humans.
• The ability to see colour stems from interactions among the three types of cones, with each cone exhibiting a preference for specific wavelengths within the visible spectrum.
• The three cone types are denoted by the initials L (responsive to long wavelengths), M (responsive to medium wavelengths), and S (responsive to short wavelengths).
  • L-type cones exhibit the highest responsiveness to light with long wavelengths, favouring wavelengths around 560 nm.
  • M-type cones exhibit the highest responsiveness to light with medium wavelengths, favouring wavelengths around 530 nm.
  • S-type cones exhibit the highest responsiveness to light with short wavelengths, favouring wavelengths around 420 nm.