Colour

About light and colour

light

• Light travels at a speed of 299,792,458 meters per second in a vacuum, but its speed decreases when it passes through a medium rather than a vacuum.
• Light-matter interactions produce various optical phenomena such as absorption, dispersion, diffraction, polarization, reflection, refraction, scattering, and transmission.
• Light is electromagnetic radiation (radiant energy), which is transported by electromagnetic waves (or their quanta, photons) and travels through space.

light & colour

• Light and colour are related but distinct concepts. Light is a form of electromagnetic radiation, while colour is a perception that results from how the human eye and brain respond to different wavelengths of visible light.
• The human eye can perceive only a small part of the electromagnetic spectrum, known as visible light, which includes wavelengths between about 400 and 700 nanometres.
• The perception of colour depends on the wavelengths of light that stimulate the cones in the retina.
• The perception of colour can vary among individuals and living organisms.
• Even if humans had never evolved, electromagnetic radiation would have been emitted by stars since the formation of the first galaxies over 13 billion years ago.
• Colour perception in humans primarily depends on the design of our eyes and the wavelength, frequency, and energy of the visible light that strikes the retina at the back of our eyes.
• Colour is a visual experience unique to each of us at any given moment because of our different points of view and perspectives on the world. So we share our experiences of colour using language to share our experiences of colour.

About white light

• White light is the term for light that contains all wavelengths of the visible spectrum at the same intensity.
• The term ‘white light’ doesn’t imply that light appears white while travelling through the air. As light travels through the air it is invisible to our eyes.
• When white light hits a neutral-coloured surface, object or medium, and all wavelengths are reflected, it appears white to the observer.

About the observation of colour

• The human eye is sensitive to the visible spectrum, which includes all the spectral colours ranging from approximately 400 to 700 nanometers.
• The sensitivity of the eye to the visible spectrum enables us to perceive colours when light interacts with objects.
• The visual perception of colour by an observer is associated with words such as red, blue, yellow, etc., which are commonly used to describe hue or dominant wavelength.
• The colour an observer sees depends on:
  • The wavelengths of visible light present in the environment.
  • The wavelengths absorbed, transmitted, or reflected by an object or medium.
• The perception of colour can be affected by factors such as brightness, contrast, and saturation, which are related to the amount of light present in a stimulus and its interaction with the eye and brain.
• The observed colour of light is determined by its wavelength, not its frequency. However, as light travels from one medium to another, such as from air to glass, the colour seen by an observer may change due to refraction causing colours to disperse in different directions.