During Stage Two emergencies, the agency can cut power to commercial customers who have agreed to interruptible contracts. The next step, when reserves fall below 1.5 percent, is a Stage Three, which triggers rotating blackouts. A Stage One is when electricity reserves dip below 7 percent, and is a request for voluntary conservation. But Monday's peak demand of more than 34,000 megawatts was close to the wintertime record, and supplies could get even tighter with colder weather looming later in the week. Part of the problem is that some power plants are out of commission while owners perform maintenance that was delayed because of summer power needs.
Estimates vary, meanwhile, as to how much holiday lights contribute to the problem.
The power agency says the lights add about 1,000 megawatts of consumption statewide. A thousand megawatts is enough to supply about 1 million homes. Not all electricity consumers are affected by the shortages. Los Angeles Department of Water and Power customers, for instance, can switch on holiday lights without fear because the municipal utility, like others in the region that are not part of the ISO grid, has more than enough electricity to meet demand.