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Light & colour

Light is electromagnetic radiation (radiant energy), which is transported by electromagnetic waves (or their quanta, photons) and travels through space.
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.

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 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.

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.

There is a difference in meaning between the terms light, electromagnetic radiation, radiant energy and electromagnetic energy in physics.

- Light is best used to refer to the subset of electromagnetic radiation that is visible to the human eye, ranging from violet (shorter wavelengths) to red (longer wavelengths).

- Electromagnetic radiation refers to the transfer of all forms of electromagnetic radiation through space by electromagnetic waves and includes gamma rays, ultraviolet (UV), infrared (IR), X-rays, and radio waves, as well as visible light.

- Radiant energy is most commonly used to refer to electromagnetic radiation carried by electromagnetic waves. Radiant energy can be measured using instruments such as photometers, which detect the intensity of light or other forms of electromagnetic radiation.

Electromagnetic energy is a more general term that refers to any form of energy that is carried by electromagnetic waves, including both radiant energy and other types of energy that are not radiant (e.g., static electric fields).

The type of energy associated with electromagnetic radiation is a measurable quantity in physics, and its measurement is essential for understanding and analyzing physical systems and processes.
The unit of measurement for electromagnetic energy in the International System of Units (SI) is the joule (J), which is defined as the amount of energy required to perform one joule of work
The electronvolt (eV) is another unit of energy commonly used in atomic and subatomic physics.