| 摘要 |
PCT No. PCT/GB96/02193 Sec. 371 Date May 20, 1998 Sec. 102(e) Date May 20, 1998 PCT Filed Sep. 6, 1996 PCT Pub. No. WO97/09868 PCT Pub. Date Mar. 13, 1997A lighting control system comprises a photosensor (12), a comparative circuit (16) and a logic switching circuit (26). The photosensor (12) produces an output (VP) which is a function of the light intensity level, and the comparative circuit (16) compares the output (VP) from the photosensor (12) with a number of preset levels (V1 to V6) in order to produce a logic output which controls the switching of the logic switching circuit (26) between four states: daylight (32), dusk (34), night (36) and dawn (38). At dusk, when the light intensity falls below a predetermined value (L2) the light is switched on. If the light intensity level then improves the light will not, however, switch off again until the light intensity rises above another higher predetermined level (L6). Similarly at dawn, the light will switch off when the light intensity rises above a predetermined value (L4) and then only switch on again if the light intensity falls below a different, lower predetermined value (L5). The problem of repeated switching on and off as a result of trasient light intensity variations at dusk and dawn is consequently avoided, without the need to introduce significant delays.
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