| light | <microscopy> Light is radiant energy of such wavelength that, falling on the retina, it stimulates the rods and cones of the eye and produces the sensation of vision. The foregoing is a physiological (subjective) definition which tells what light does, under certain conditions, rather than what it is. According to the (objective) Maxwell theory, all radiant energy is electromagnetic in character, the generation of the radiation depending upon the portion of the spectrum under consideration. For that part of the spectrum lying within the visual range, approximately 400 to 700 nanometres (nm) the release of light energy from externally stimulated sources may be thought of as due to atomic or molecular vibration or to the passing of electrons from high to lower energy levels accompanied by the spasmodic release of energy as the electronic orbits decrease in diameter. See: quantum theory. (05 Aug 1998) |
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| light adaptation | The visual adjustment occurring under increased illumination in which the retinal sensitivity to light is reduced. See: light-adapted eye. Synonym: photopic adaptation. (05 Mar 2000) |
| light bath | Therapeutic exposure of the skin to radiant light. (05 Mar 2000) |
| light cells of thyroid | Cell's present between follicles or interspersed among follicular cell's; they are rich in mitochondria and are believed to be the source of thyrocalcitonin. Synonym: C cell, light cells of thyroid. (05 Mar 2000) |
| light chain | <immunology, protein> The lighter of the two types of polypeptide chains that are found in immunoglobulin and antibody molecules. Also used as a non-specific term for the smaller subunits of several multimeric proteins such as immunoglobulin, myosin, dynein, clathrin. (14 Oct 1997) |
| light chain-related amyloidosis | A form of primary amyloidosis in which the fibrillar amyloid deposits are derived from the amino terminal variable region of the light chains of immunoglobulin; seen in B-lymphocyte and plasma-cells dyscrasias. (05 Mar 2000) |
| light coagulation | The coagulation of tissue by an intense beam of light, including laser (laser coagulation). In the eye it is used in the treatment of retinal detachments, retinal holes, aneurysms, haemorrhages, and malignant and benign neoplasms. (12 Dec 1998) |
| light dependent reaction | The reaction taking place in the chloroplast in which the absorption of a photon leads to the formation of ATP and NADPH. (18 Nov 1997) |
| light difference | The difference in light sensitivity of the two eyes. Synonym: brightness difference threshold. (05 Mar 2000) |
| light differential threshold | The smallest difference in light intensity that can be appreciated. (05 Mar 2000) |
| light green SF yellowish | An acid arylmethane dye, used as a cytoplasmic stain in plant and animal histology; fades badly in bright light. (05 Mar 2000) |
| light harvesting system | Set of photosynthetic pigment molecules that absorb light and channel the energy to the photosynthetic reaction centre, where the light reactions of photosynthesis occur. In higher plants, contains chlorophyll and carotenoids and is present in two slightly different forms in photosystems I and II. (18 Nov 1997) |
| light metal | A metal with a specific gravity of less than 4. (05 Mar 2000) |
| light microscope | <instrument> The most common type of microscope (a device used to magnify small objects or substances) used in laboratories. The device works by passing visible light through a condenser and an objective lens. (09 Oct 1997) |
| light microscopy | <procedure> In contrast to electron microscopy. See: bright field, phase contrast, interference, interference contrast, interference reflection, dark field, confocal and fluorescence microscopy. (18 Nov 1997) |
| alternating light test | Test to detect a relative afferent defect in one eye by watching pupillary movements. With the patient fixing in the distance, the light is held on each eye for about a second, and quickly moved to the other eye. Assuming no defect of the innervation to the iris sphincter in one eye (which would produce an anisocoria in light), the eye with the weaker light response has a relative afferent pupillary defect. This asymmetry of pupillomotor input can be estimated by holding neutral density filters in front of the better eye until the pupillary responses of the two eyes are balanced. Synonym: swinging light test. (05 Mar 2000) |
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| Begg light wire differential force technique | An orthodontic appliance utilizing small gauge labial wires with expansion and contraction loops formed into it and attached to bands fitted to individual teeth; sometimes called Begg light wire differential force technique. (05 Mar 2000) |
| gene rearrangement, b-lymphocyte, light chain | Ordered rearrangement of b-lymphocyte variable gene regions coding for the kappa or lambda light chains, thereby contributing to antibody diversity. It occurs during the second stage of differentiation of the immature b-lymphocyte. (12 Dec 1998) |
| ray, light | <microscopy> The term applied to the lines perpendicular to the wavefronts of waves of light to indicate their direction of travel in an isotropic medium. Note the wave normal and the ray do not coincide in isotropic media. (05 Aug 1998) |
| reflected light | Light directed backward from a mirror. (05 Mar 2000) |
| refracted light | Bent rays of light changed in passage from one transparent medium to another of unequal density. See: refraction. (05 Mar 2000) |
| visible light | <physics> Electromagnetic radiation with wavelengths between 400 nanometres and 750 nanometres. Electromagnetic radiation within this range can be detected by the human eye. Colours depend on the wavelength lengths, a short wavelength (the 400 nm side) looks blue and a long wavelength (the 750 nm side) looks red. (09 Oct 1997) |
| metals, light | Metals with low specific gravity, typically smaller than 5, characterised by a single valence (1, 2, or 3), a simple spectrum, strong electromotive force (positive), and colourless compounds. (12 Dec 1998) |
| minimum light | Threshold of visual sensation, the minimal light intensity evoking a visual sensation. Synonym: achromatic threshold, minimum light threshold. (05 Mar 2000) |
| minimum light threshold | Threshold of visual sensation, the minimal light intensity evoking a visual sensation. Synonym: achromatic threshold, minimum light threshold. (05 Mar 2000) |
| cold light | Fluorescent light as opposed to incandescent light. (05 Mar 2000) |
| monochromatic light | <microscopy> Light composed of one wavelength. It may be obtained by the use of a laser or by gaseous discharge tubes in combination with proper filters. An approximation is obtained by interference filters or monochromators. (05 Aug 1998) |
| plane-polarized light | <chemistry> Light which is passed through a filter which blocks out all the light except that which ocillates in one plane. (09 Jan 1998) |
| cone of light | A triangular area at the anterior inferior part of the tympanic membrane, running from the umbo to the periphery, where there is seen a bright reflection of light. Synonym: cone of light, light reflex, Politzer's luminous cone, red reflex, Wilde's triangle. Malacarne's pyramid, a lobule on the undersurface of the cerebellum, the posterior portion of the vermis. (05 Mar 2000) |
| Wood's light | Ultraviolet light produced by Wood's lamp. (05 Mar 2000) |