| photonosus | Any disease caused by excessive exposure to or unusual intensity of light, or resulting from phototoxicity or photoallergy. Synonym: photopathy. Origin: photo-+ G. Nosos, disease (05 Mar 2000) |
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| photons | Discrete concentrations of energy, apparently massless elementary particles, that move at the speed of light. They are the unit or quantum of electromagnetic radiation. Photons are emitted when electrons move from one energy state to another. (12 Dec 1998) |
| photooxidase | <enzyme> Rhodoquinone accepts electrons from ubiquinone during chromatophore photooxidase activity Registry number: EC 1.6.99.- Synonym: rhodoquinone photooxidase (26 Jun 1999) |
| photopathy | Synonym: photonosus. Origin: photo-+ G. Pathos, suffering (05 Mar 2000) |
| photopeak | The characteristic energies of photons emitted by a radionuclide, used to set scanning parameters. (05 Mar 2000) |
| photoperceptive | Capable of both receiving and perceiving light. (05 Mar 2000) |
| photoperiod | <ecology> Recurring cycle of light and dark periods. The natural photoperiod is approximately 24 hours, and the ratio of light to dark hours slowly changes over the course of a year. In controlled experiments, the photoperiod is usually (but not necessarily) retained at 24 hours, and the light:dark ratio is typically constant. (09 Oct 1997) |
| photoperiodism | <biology> Events triggered by duration of illumination or pattern of light/dark cycles: often the wavelength of the illuminating light is important as for example in control of circadian rhythm in plants. See: phytochromes. (18 Nov 1997) |
| photopheresis | A process in which peripheral blood is exposed in an extracorporeal flow system to photoactivated 8-methoxypsoralen (methoxsalen) and ultraviolet light - a procedure known as puva therapy. Photopheresis is at present a standard therapy for advanced cutaneous T-cell lymphoma; it shows promise in the treatment of autoimmune diseases. (12 Dec 1998) |
| photophobia | <psychology, symptom> An abnormal visual intolerance of light. Origin: Gr. Phobos = fear (16 Mar 1998) |
| photophobic | Relating to or suffering from photophobia. (05 Mar 2000) |
| photophone | <physics> An apparatus for the production of sound by the action of rays of light. Origin: Photo- + Gr. Sound. Source: Websters Dictionary (01 Mar 1998) |
| photophore | 1. A lamp with reflector used in laryngoscopy and in the examination of other internal parts of the body. 2. In bacteriology, the organ producing intracellular bioluminescence in certain organisms. Origin: photo-+ G. Phoros, bearing (05 Mar 2000) |
| photophoresis | See: extracorporeal photophoresis. Extracorporeal photophoresis, destruction of cells separated from blood in an extracorporeal flow system by ultraviolet activation of chemotherapeutic agents such as psoralens. (05 Mar 2000) |
| photophosphorylation | <plant biology> The synthesis of ATP that takes place during photosynthesis. In noncyclic photophosphorylation the photolysis of water produces electrons that generate a proton motive force which is used to produce ATP, the electrons finally being used to reduce NADP to NADPH. When the cellular ratio of reduced to nonreduced NADP is high, cyclic photophosphorylation occurs and the electrons pass down an electron transport system and generate additional ATP, but no NADPH. (31 Dec 1997) |