Reposting:

According to Energy Australia, “a brownout occurs when the voltage is at half strength for more than one second” resulting in dim lights and a shrinking picture in your TV. Dennis S. Gana, manager of corporate communications at National Power Corporation (Philippines) explains that the two terms are used interchangeably in the country. “The term ‘brownout’ is used only when the power outage is localised, involving small areas. The outages during brownouts involve only distribution lines, not generators. Blackouts are usually caused by power generators and/or power transmission systems, and they cover a wider area,” he says.

Source: Reader’s Digest Asia, April 2009