Power symbol

How to read it

The circle broken at the top by a vertical line is IEC 60417-5009. The International Electrotechnical Commission defines it for a power switch that does not do a total mains disconnect, so the device still consumes standby power when it is off. IEEE 1621, the standard for power controls on office and consumer electronics, keeps the symbol and says it is generally used and understood to mean power, as on power buttons and indicators. It is the symbol on most power buttons, and Unicode encodes it as U+23FB, the power symbol.

Also searched as: power button symbol, standby symbol.

Standby or power

The two standards give the same shape different names. IEC 60417 (also published as ISO 7000) calls it standby; IEEE 1621 calls it power. The 2014 proposal to add the symbols to Unicode, written by Terence Eden, Joe Loughry and Bruce Nordman of Lawrence Berkeley National Laboratory, acknowledged the dispute and said the devices that use it to mean power far outnumber the ones that use it for standby. Unicode’s chart lists both readings under the one character.

Why standby was replaced

Nordman and Alan Meier of Lawrence Berkeley National Laboratory proposed redefining the symbol to mean power in a 2002 report for the California Energy Commission, the work that became IEEE 1621. Their reason was the word standby itself: on some copiers standby meant fully on and ready, on some computers and monitors it meant a low-power mode that takes time to recover, and standby power was also used for a device’s lowest power state, often off. The Unicode proposal adds that standby is routinely used to mean off, sleep, on and other things. The report settled on three power states, on, sleep and off, with a crescent moon, the Sleep symbol, for sleep.

Off can still use power

In the draft standard in the same report, this symbol is for a power button whose off state is soft-off (the device may still use some power), may vary, or is unknown. Lawrence Berkeley National Laboratory describes standby power as electricity used by appliances while they are switched off or not doing their main job, for things like a remote-control receiver, a clock or a display.

Look-alikes

The Power on/off symbol symbol has the line inside a circle that is not broken. In the 2002 draft of IEEE 1621 it is for a switch that always goes to hard-off, using no power at all.