Light

Light (also called iftiin in Somali) is a form of electromagnetic radiation. Strictly defined, light is the portion of electromagnetic radiation that the human eye can detect. In broader usage, the term refers to any radiation of the same type, including ultraviolet and infrared, which the eye cannot see.

Light travels at a definite speed when passing through a vacuum. This speed is denoted 'c' and is approximately 300,000 kilometres per second. Modern physics recognizes this speed as an upper limit that cannot be exceeded by any information or object.

Wave-particle duality

Light has two complementary properties. In one respect it behaves as a wave: it has wavelength and frequency, and it exhibits diffraction and interference. In another respect it behaves as discrete packets of energy called photons, evident when light interacts with matter such as in the photoelectric effect. Quantum physics reconciles these two aspects in a single framework.

Colour and wavelength

The colour of visible light depends on its wavelength. Shorter wavelengths appear blue and violet, while longer wavelengths appear red. White light, such as that from the sun, is a mixture of different wavelengths; when separated by a prism or a rainbow, they disperse into a spectrum of colours.

Behaviour of light

When light strikes an object, it can be reflected, refracted (bent as it passes through a medium), absorbed, or scattered. These phenomena underlie the function of mirrors, lenses, cameras, telescopes, and eyes. The refraction of light also explains why objects in water appear bent.

Sources of light and applications

Light is emitted by incandescent objects such as the sun and lamp filaments, or by electronic devices such as LEDs and lasers. Life on Earth depends on sunlight, which plants use during photosynthesis. In modern technology, light is transmitted through fibre-optic cables to convey information, and is used in medical research and precision measurement.