photopositive, a.
(fəʊtəʊˈpɒzɪtɪv)
Also with hyphen.
[f. photo- 1 + positive a. and n.]
1. Zool. Of an animal: tending to move towards light.
| 1914 [see photonegative a. 1]. 1923 Jrnl. Exper. Zool. XXVIII. 194 The photopositive reactions of insects under normal conditions usually result in their escape from places of danger. 1964 Oceanogr. & Marine Biol. II. 482 The larvae [of Spirorbis] may settle or may resume their pelagic existence, again becoming photopositive for a short time. 1975 [see photonegative a. 1]. |
2. Physics. Pertaining to or exhibiting an increase in electrical conductivity when illuminated.
| 1915 [see photonegative a. 2]. 1932 Hughes & DuBridge Photoelectric Phenomena viii. 328 The effect of light [on photoconducting substances] is usually to increase the conductivity (the photopositive effect..), but occasionally it is found that light apparently diminishes the conductivity (the photonegative effect..). The photonegative effect occurs above a critical voltage whose value depends on the temperature. |
Hence photoˈpositively adv.; ˌphotoposiˈtivity.
| 1946 Nature 13 July 58/2 When behaving photopositively Hydra orientates itself klinokinetically. 1962 Jrnl. Insect Physiol. VIII. 251 Photopositivity declines continuously within each instar, but shows an increase after each moult. |