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.