| 摘要 |
<p>A switching control cicuit (4) for energizing a lamp (24) in response to a decrease in ambient light below a predetermined level includes a photosensor (70) and a timer circuit (30) that responds to the photosensor (70) indicating that the ambient light level is below a predetermined level by gating a solid state switching device (53) into conductance to energize the lamp (24). The photosensor (70) is powered by the signal that gates the switching device (53) in a manner that renders the photosensor operative only when lamp (24) is not energized. Therefore, the lamp (26) is energized upon the onset of dusk for a predetermined period of time during which the photosensor (70) is disabled. After the period of time has expired, the lamp (26) is deenergized and the photosensor (70) is again enabled for a brief period of time to determine whether ambient light is still below the predetermined level. If it is, the light is again energized for another period of time. If not, the light remains deenergized.</p> |
