| usable light range | <microscopy> The ratio of the maximum to the minimum levels of illuminance over which a video camera or camera tube can provide a usable signal. Being aided by automatic irises, gray-wedge wheels, etc., in addition to varying electrode voltages where permissible, the usable light range can be several orders of magnitude greater than the intrascene dynamic range. See: intrascene dynamic range, condenser, variable-focus. (05 Aug 1998) |
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| flux, light | <microscopy> Sometimes called luminous flux, the visible portion of the radiant energy emitted by a light source. It is measured in lumens per solid angle. In electrical engineering, it is analogous to the lines of force in a magnetic field, spoken of as magnetic flux. (05 Aug 1998) |
| 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) |
| light-activated resin | A resin which uses visible or ultraviolet light to excite a photoinitiator which interacts with an amine to form free radicals and initiate polymerization. Used mainly in restorative dentistry. Synonym: light-activated resin. (05 Mar 2000) |
| 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-adapted eye | An eye that has been exposed to light, with bleaching of rhodopsin (visual purple) and insensitivity to low illumination. Synonym: photopic eye. (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 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-cured resin | A resin which uses visible or ultraviolet light to excite a photoinitiator which interacts with an amine to form free radicals and initiate polymerization. Used mainly in restorative dentistry. Synonym: light-activated resin. (05 Mar 2000) |
| 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) |