All light propagates at a finite speed. Even moving observers always measure the same value of c, the speed of light in vacuum, as c = 299,792,458 metres per second (186,282.397 miles per second). When light passes through a transparent substance, such as air, water or glass, its speed is reduced, and it undergoes refraction. The reduction of the speed of light in a denser material can be indicated by the refractive index, n, which is defined a ...

See also:

Light, Light - Visible electromagnetic radiation, Light - Speed of light, Light - Refraction, Light - Optics, Light - Color and wavelengths, Light - Measurement of light, Light - Light sources, Light - Theories about light, Light - Early Greek ideas, Light - 10th century optical theory, Light - The 'plenum', Light - Particle theory, Light - Wave theory, Light - Electromagnetic theory, Light - Particle theory revisited, Light - Quantum theory, Light - Wave-particle duality, Light - A light wave

Read more here: » Light: Encyclopedia II - Light - Refraction

See also:

Refractive index, Refractive index - The speed of light, Refractive index - Dispersion and Absorption, Refractive index - Anisotropy, Refractive index - Nonlinearity, Refractive index - Inhomogeneity, Refractive index - Applications, Refractive index - External link

Read more here: » Refractive index: Encyclopedia II - Refractive index - The speed of light

The refractive index of certain media may be different depending on the polarization and direction of propagation of the light through the medium. This is known as birefringence or anisotropy and is described by the field of crystal optics. In the most general case, the dielectric constant is a rank-2 tensor (a 3 by 3 matrix), which cannot simply be described by refractive indices except for polarizations along principal axes. In magneto-optic (gyro-magnetic) and optically active materials, the principal axes are complex (corre ...

See also:

Refractive index, Refractive index - The speed of light, Refractive index - Dispersion and Absorption, Refractive index - Anisotropy, Refractive index - Nonlinearity, Refractive index - Inhomogeneity, Refractive index - Applications, Refractive index - External link

Read more here: » Refractive index: Encyclopedia II - Refractive index - Anisotropy

Light is electromagnetic radiation with a wavelength that is visible to the eye (visible light) or, in a technical or scientific context, electromagnetic radiation of any wavelength. The three basic dimensions of light (i.e., all electromagnetic radiation) are: Intensity (or brilliance or amplitude), which is related to the human perception of brightness of the light, Frequency (or wavelength), perceived by humans as the color of the light, and Polarization (or angle of vibration), which is not perceptible by ...

Including:

• Light - Visible electromagnetic radiation
• Light - Speed of light
• Light - Refraction
• Light - Optics
• Light - Color and wavelengths
• Light - Measurement of light
• Light - Light sources
• Light - Theories about light
• Light - Early Greek ideas
• Light - 10th century optical theory
• Light - The 'plenum'
• Light - Particle theory
• Light - Wave theory
• Light - Electromagnetic theory
• Light - Particle theory revisited
• Light - Quantum theory
• Light - Wave-particle duality
• Light - A light wave

Read more here: » Light: Encyclopedia - Light

Girl Indigo

Shattered glass sparkles

through a broken window

refracting reflections

into backlit hallways

deep, deep inside, flashing

strophic light, then dark.

A figure, a shape moves

into and out of shadow

a child, a woman reverberates

in silhouette.

Broken nail, broken heart

her hair, dyed jet black, fades

in heartbeats and tears.

She is here, she is now

screaming forever.

Dimensionless and expanding

beyond the edge of visible light

she hovers in her own luminescence

untouchable, yet yearning an embrace

Beyond a grasp, colors fail

pastels wither and crimsons bleed

into neutral shades of gray

as she absorbs the sun

into her deepest indigo.

(See also: Indigo Children, What is Indigo Children, Parenting Indigo Children, Adult Indigo, Indigo Children Channeling)

Birefringence, or double refraction, is the decomposition of a ray of light into two rays (the ordinary ray and the extraordinary ray) when it passes through certain types of material, such as calcite crystals, depending on the polarization of the light. This effect can occur only if the structure of the material is anisotropic. If the material has a single axis of anisotropy, (i.e. it is uniaxial,) birefringence can be formalised by assigning two different refractive indices to the material for diff ...

Including:

• Birefringence - Electromagnetic waves in an anisotropic material
• Birefringence - Examples of birefringent materials
• Birefringence - Biaxial birefringence
• Birefringence - Measuring birefringence
• Birefringence - Birefringence in fiber optics

Read more here: » Birefringence: Encyclopedia - Birefringence

The lens or crystalline lens is a transparent, biconvex structure in the eye that, along with the cornea, helps to refract light to focus on the retina. In humans, the refractive power of the lens in its natural environment is approximately 15 dioptres, roughly one-fourth of the eye's total power. The lens is flexible and its curvature is controlled by ciliary muscles. By changing the curvature of the lens, one can focus the eye on objects at different dis ...

Including:

• Lens anatomy - Diseases

Read more here: » Lens anatomy: Encyclopedia - Lens anatomy

The word caustics, meaning "to burn" or "burning", may refer to: Caustic (substance), a substance that 'eats away' or chemically burns other materials by process of attacking it basically Caustic (optics), a bundle of light rays Caustic, in differential geometry, the envelope of rays either reflected or refracted by a manifold. It is related to the optical concept of caustics Sodium hydroxide, sometimes called caustic soda Other related archive

Read more here: » Caustics: Encyclopedia - Caustics

The cornea is the transparent front part of the eye that covers the iris, pupil, and anterior chamber and provides most of an eye's optical power [1]. Together with the lens, the cornea refracts light and consequently helps the eye to focus. The cornea gives a larger contribution to the total refraction than the lens, but whereas the curvature of the lens can be adjusted to "tune" the focus, the curvature of the cornea is fixed. The cornea has sensitive nerve endings; touch of the cornea causes an involuntary reflex to close th ...

Including:

• Cornea - Layers of the cornea
• Cornea - Surgical procedures involving the cornea
• Cornea - Non-surgical procedures involving the cornea
• Cornea - Diseases and disorders

Read more here: » Cornea: Encyclopedia - Cornea

A telescope (from the Greek tele = 'far' and skopein = 'to look or see'; teleskopos = 'far-seeing') is an optical tool which gathers and focuses electromagnetic radiation. Telescopes increase the apparent angular size of distant objects, as well as their apparent brightness. Telescopes are used for astronomy and in many non-astronomical instruments including theodolites, transits, spotting scopes, monoculars, binoculars, camera lenses and spyglasses. The word "telescope" usually refers to optical telescopes, but there are telescopes for mo ...

Including:

• Telescope - History
• Telescope - Types
• Telescope - Telescope mountings
• Telescope - Research telescopes
• Telescope - Imperfect images
• Telescope - The five Seidel aberrations
• Telescope - The chromatic aberrations
• Telescope - Famous optical telescopes
• Telescope - Related lists

Read more here: » Telescope: Encyclopedia - Telescope

A Darkfield microscope uses a method whereby the sample being viewed is actually in front of a dark background and light is being angled onto the specimen from the sides. Stains cannot be used in this method as the specimen-cell becomes dead during the staining. In dark field microscopy light is prevented from entering the central region by placing a disc in the condensor. Thus the main field of obsevation becomes dark. The light entering from the peripheral region of the condenser becomes refracted and reflected. The te ...

Read more here: » Darkfield microscope: Encyclopedia - Darkfield microscope

Chromatic aberration is caused by the dispersion of the lens material, the variation of its refractive index n with the wavelength of light. The term purple fringing is also commonly used. Since the focal length f of a lens is dependent on n, different wavelengths of light will be focused on different positions. Chromatic aberrations can be both longitudinal, in that different wavelengths are focused at a different distance from the lens; and transverse or lateral, in that different wavelengths are focused at different positions in the focal plane (because ...

Including:

• Chromatic aberration - External link

Read more here: » Chromatic aberration: Encyclopedia - Chromatic aberration

An X-ray microscope uses electromagnetic radiation in the soft X-ray band to produce images of very small objects. Unlike visible light microscopes, X-rays do not reflect or refract easily, and they are invisible to the human eye. Therefore the basic process of an X-ray microscope is to expose film or use a charge-coupled device (CCD) detector to detect X-rays that pass through the specimen, rather than light which bounces off the specimen. Early X-ray microscopes by Kirkpatrick and Baez used grazing-incidence reflective optics ...

Read more here: » X-ray microscope: Encyclopedia - X-ray microscope

Allvar Gullstrand (born June 5, 1862 in Landskrona – died July 28, 1930 in Stockholm) was a Swedish ophthalmologist. He was professor (1894–1927) successively of eye therapy and of optics at the University of Uppsala. He applied the methods of physical mathematics to the study of optical images and of the refraction of light in the eye. For this work he received the Nobel Prize in Physiology or Medicine in 1911. Gullstrand is noted also for his research on astigmatism and for improving the ophthalmoscope and corrective lenses for use after removal of a cataract from the eye. He i ...

Including:

• Allvar Gullstrand - External link

Read more here: » Allvar Gullstrand: Encyclopedia - Allvar Gullstrand

A Zone plate is a device used to focus light. Unlike lenses however, zone plates use diffraction instead of refraction. Created by Augustin-Jean Fresnel, they are sometimes called Fresnel zone plates in his honor. The zone plate's focusing ability is an extension of the Arago spot phenomenon caused by diffraction from an opaque disc. A zone plate consists of a set of radially symmetric rings, known as Fresnel zones, which alternate between opaque and transparent. Light hitting the zone plate will diffract around the opaq ...

Including:

• Zone plate - Design and manufacture
• Zone plate - Applications
• Zone plate - Physics
• Zone plate - Photography

Read more here: » Zone plate: Encyclopedia - Zone plate

Myopia is a refractive defect of the eye in which light focuses in front of the retina. Those with myopia are often described as nearsighted or short-sighted in that they typically can see nearby objects clearly but distant objects appear blurred because the lens cannot flatten enough. The opposite of myopia is hyperopia or "farsightedness". Myopia is the most common eyesight problem in the world. About one quarter of the adult population in the United States has myopia. In places like Japan, Singapore and Taiwan, as m ...

Including:

• Myopia - Prevalence
• Myopia - Pathogenesis
• Myopia - Theories
• Myopia - Relevant research
• Myopia - Night myopia
• Myopia - Myopia and IQ

Read more here: » Myopia: Encyclopedia - Myopia

Aberration in optical systems (lenses, prisms, mirrors or series of them intended to produce a sharp image) generally leads to blurring of the image. It occurs when light from one point of an object after transmission through the system arrives in different points. Instrument-makers need to correct optical systems to compensate for aberration. The articles reflection, refraction and caustic discuss the general features of reflected and refracted rays. Aberrations fall into two classes: chromatic aberrations ...

Including:

• Aberration in optical systems - Monochromatic aberration
• Aberration in optical systems - Aberration of axial points spherical aberration in the restricted sense
• Aberration in optical systems - Aberration of elements i.e. smallest objects at right angles to the axis
• Aberration in optical systems - Aberration of lateral object points points beyond the axis with narrow pencils. Astigmatism.
• Aberration in optical systems - Aberration of lateral object points with broad pencils. Coma.
• Aberration in optical systems - Curvature of the field of the image
• Aberration in optical systems - Distortion of the image
• Aberration in optical systems - Analytic treatment of aberrations
• Aberration in optical systems - Practical elimination of aberrations
• Aberration in optical systems - Chromatic or colour aberration
• Aberration in optical systems - Authorities.

Read more here: » Aberration in optical systems: Encyclopedia - Aberration in optical systems

Silk is a natural protein fibre that can be woven into textiles. It is obtained from the cocoon of the silkworm larva, in the process known as sericulture, which kills the larvae. The shimmering appearance for which it is prized comes from the fibers' triangular prism-like structure, which allows silk cloth to refract incoming light at different angles. Silk - Early history. Silk was first developed in early China, possibly as early as 6000 BC and definitely by 3000 BC. Legend gives credit to a Chine ...

Including:

• Silk - Early history
• Silk - Silk trade
• Silk - Secret
• Silk - Wild Silks
• Silk - Europe
• Silk - North America
• Silk - World War
• Silk - Islam
• Silk - Animal rights
• Silk - Other uses
• Silk - Stazione Bacologica Sperimentale

Read more here: » Silk: Encyclopedia - Silk

In real materials, the polarization does not respond instantaneously to an applied field. This causes dielectric loss, which can be expressed by a permittivity that is both complex and frequency dependent. Real materials are not perfect insulators either, i.e. they have non-zero direct current conductivity. Taking both aspects into consideration, we can define a complex index of refraction: Here, n is the refractive index indicating the phase velocity as above, while κ is called the extinction coeff ...

See also:

Refractive index, Refractive index - The speed of light, Refractive index - Dispersion and Absorption, Refractive index - Anisotropy, Refractive index - Nonlinearity, Refractive index - Inhomogeneity, Refractive index - Applications, Refractive index - External link

Read more here: » Refractive index: Encyclopedia II - Refractive index - Dispersion and Absorption

The refractive index of a material is the most important property of any optical system that uses refraction. It is used to calculate the focusing power of lenses, and the dispersive power of prisms. For a solution of sugar, the refractive index can be used to determine the sugar content (see Brix). The refractive index is also used in chemistry to determine the purity of chemicals. ...

See also:

Refractive index, Refractive index - The speed of light, Refractive index - Dispersion and Absorption, Refractive index - Anisotropy, Refractive index - Nonlinearity, Refractive index - Inhomogeneity, Refractive index - Applications, Refractive index - External link

Read more here: » Refractive index: Encyclopedia II - Refractive index - Applications