brownout

 darkness resulting from the extinction of lights (as in a city invisible to enemy aircraft).  [WordNet 1.5]

 a partial reduction in the amount of electric power available to customers in a region, such as by reduction of voltage or selective cutoff of certain customers; -- it occurs for example in summer when the demand for electricity for air-conditioning exceeds the supply, or when power to certain customers is cut off by a severe storm. It is contrasted with blackout, which is the total loss of electrical power in a region.  [PJC]