Question

What is light? You can start by describing the different historic models for light and explain their individual strength and shortcomings in explaining observable phenomena. Then, try to summarize our current quantum mechanic understanding and highlight its implications for all matter and energy. Finally, consider identifying visible light within the electromagnetic (EM) spectrum and discuss applications that may depend on different light effects such as photoelectric or electro-luminescent effect.

Answer 1

Light is part of the electromagnetic spectrum, which ranges from radio waves to gamma rays.

Aristotle

The essence of light is white light.
Colors are made up of a mixture
of lightness and darkness.

Newton

Light is comprised of colored particles.

Huygen

Light is a wave.

Young

Proof of the wave theory of light.

Maxwell

Predicted the existence
of electromagnetic waves.

Einstein

Light is a photon

quantum mechanics explains the behavior of matter and its interactions with energy on the scale of atoms and subatomic particles.

Light behaves in some aspects like particles and in other aspects like waves. Matter—the "stuff" of the universe consisting of particles such as electrons and atoms—exhibits wavelike behavior too. Some light sources, such as neon lights, give off only certain specific frequencies of light, a small set of distinct pure colors determined by neon's atomic structure. Quantum mechanics shows that light, along with all other forms of electromagnetic radiation, comes in discrete units, called photons, and predicts its spectral energies (corresponding to pure colors), and the intensities of its light beams. A single photon is a quantum, or smallest observable particle, of the electromagnetic field.

Applications

Electroluminescent technologies have low power consumption compared to competing lighting technologies, such as neon or fluorescent lamps. This, together with the thinness of the material, has made EL technology valuable to the advertising industry.

Electroluminescent lighting is now used as an application for public safety identification involving alphanumeric characters on the roof of vehicles for clear visibility from an aerial perspective

Photoelectric cells were originally used to detect light, using a vacuum tube containing a cathode, to emit electrons, and an anode, to gather the resulting current.

Imaging technology, including (older) television camera tubes or image intensifiers

Studying nuclear processes