Brownout

A brownout is a reduction in electrical voltage in a power system, typically temporary, that causes lights to dim. It can be intentional or unintentional and is distinct from a blackout, which is a complete loss of power. Voltage sags during a brownout generally fall below about 90 percent of the nominal level, though exact thresholds vary by country and equipment.

Causes of brownouts include high demand on the electrical grid during peak times, faults or congestion on transmission and distribution lines, failures or adjustments in voltage regulation equipment, and protective actions taken to prevent wider outages. Utilities may purposefully lower voltage in a controlled manner during tight supply conditions to conserve resources or stabilize the grid. Weather events, generator outages, and miscoordination among network components can also produce brownouts, especially in areas with aging infrastructure or limited transmission capacity.

Effects of brownouts can range from minor to significant. Lights dim and electronic devices may behave erratically or reset. Motors in appliances and industrial equipment can stall or overheat, potentially shortening equipment life if undervoltage conditions persist or recur. Sensitive electronics and power supplies may be vulnerable to damage or data loss during voltage fluctuations, though many modern devices include protection features.

Prevention and mitigation involve both utility and consumer actions. Utilities employ voltage regulation techniques such as tap-changing transformers, reactive power control, and capacitor banks, along with demand-response programs to maintain stable voltage. Consumers can use uninterruptible power supplies, voltage regulators, and properly sized protection devices, and businesses may rely on backup generation or energy storage to ensure continuity during voltage fluctuations.