Light

Physical phenomenon of electromagnetic radiation

A prism dispersing light into a spectrum of colors.

Light is a form of electromagnetic radiation that is visible to the human eye and is responsible for the sense of sight. It is a small part of the electromagnetic spectrum and is typically defined as having wavelengths in the range of 400–700 nanometers (nm), or 4.00 × 10⁻⁷ to 7.00 × 10⁻⁷ meters, between the infrared (with longer wavelengths) and the ultraviolet (with shorter wavelengths).

Properties of Light

Light exhibits both wave and particle properties, a phenomenon known as wave-particle duality. This dual nature is a fundamental concept in quantum mechanics.

Wave Properties

Light behaves as a wave, which can be described by its wavelength, frequency, and speed. The speed of light in a vacuum is approximately 299,792,458 meters per second (m/s), and it is one of the fundamental constants of nature.

The electromagnetic spectrum, with visible light highlighted.

Particle Properties

Light also behaves as a stream of particles called photons. Photons are massless particles that carry energy and momentum, and their energy is proportional to the light's frequency.

Interaction with Matter

Light interacts with matter in various ways, including reflection, refraction, diffraction, and absorption.

Reflection

Reflection occurs when light bounces off a surface. The angle of incidence is equal to the angle of reflection, a principle known as the law of reflection.

Refraction

Refraction is the bending of light as it passes from one medium to another with a different refractive index. This phenomenon is responsible for the focusing of light by lenses and the formation of rainbows.

Refraction of light at the surface of water.

Diffraction

Diffraction is the bending of light around obstacles and the spreading of light waves when they pass through small openings. This effect is more pronounced when the size of the obstacle or opening is comparable to the wavelength of the light.

Absorption

Absorption occurs when light is absorbed by a material, converting the light energy into other forms, such as heat. Different materials absorb different wavelengths of light, which is why objects have different colors.

Sources of Light

Light can be produced by various sources, both natural and artificial.

Natural Sources

The primary natural source of light is the Sun, which emits light through the process of nuclear fusion. Other natural sources include stars, bioluminescence in organisms, and lightning.

Natural light illuminating a landscape.

Artificial Sources

Artificial sources of light include incandescent bulbs, fluorescent lamps, LEDs, and other forms of electric lighting.

Artificial lighting at night.

Historical Theories of Light

The nature of light has been a subject of study and debate for centuries.

Early Theories

In ancient times, philosophers like Empedocles and Euclid proposed theories about light and vision. Empedocles suggested that light was emitted from the eye, while Euclid believed in the rectilinear propagation of light.

Particle Theory

Isaac Newton proposed the particle theory of light, suggesting that light is composed of small particles. This theory explained reflection and refraction but struggled with diffraction and interference.

Wave Theory

Christiaan Huygens proposed the wave theory of light, which explained phenomena like diffraction and interference. Huygens' principle describes how wavefronts propagate through space.

Christiaan Huygens, proponent of the wave theory of light.

Quantum Theory

In the 20th century, the development of quantum mechanics led to the understanding of light as having both wave and particle properties. Albert Einstein's explanation of the photoelectric effect provided evidence for the particle nature of light.

Related Pages

• Electromagnetic spectrum
• Photon
• Optics
• Quantum mechanics
• Wave-particle duality