Updated: 11/13/2018 by Computer Hope
LED status lights

Short for light-emitting diode, LED is a semiconductor that illuminates when an electrical charge passes through it. LEDs are commonly green, amber or red; however can be an assortment of other colors. Below are examples of how an LED could be used with a computer.

Keyboard LEDs

Keyboard light emitting diode or LED

A good example of an LED is the led status indicators on your keyboard for Num Lock, Caps Lock and Scroll Lock as shown in the picture. In this picture, the blue LED on the keyboard indicates the Num Lock is enabled, but since the Caps Lock and Scroll Lock are not on it indicates they are not enabled. The location of these indicators depend on manufacturer of the keyboard, but are usually located in the top center or top-right hand side of the keyboard.


Not all keyboard num lock, caps lock, or scroll lock indicators have identifiers like those shown in the picture. If you are not sure what LED goes to what key, press the num lock, caps lock, or scroll lock key while watching the LED's and see which one illuminates.


Apple keyboards and some other keyboards have the Caps Lock LED indicator on the Caps Lock key and may not have other indicators because there are no scroll lock or num lock keys.

Mouse LED

Most computers today use an optical mouse, which is a mouse that uses an LED to help track the cursor on the screen.

Motherboard LED

Motherboard LED

Many motherboards also have an onboard LED that lets anyone looking at the motherboard know that there is power getting to the motherboard and in some cases if there are errors. Pictured at right is an LED/PLED located between the PCI slots on a motherboard.


Do not work inside a computer or disconnect any internal plugs while this LED is lit.


When the power cable is disconnected from the computer the LED light stays on for several seconds and then slowly fade off, which is normal.

Floppy, hard drive, CD-ROM, and other drives LED

Computer floppy drives and CD-ROM drives have LED indicators on the front of them to help indicate when the data on a disk or disc is being read, or information is being written to the disc.

A hard drive has no LED on the drive, but the motherboard send signals over the system panel connector cables that cause an LED on the front of a computer to flash when the drive is active.

Printer, speakers, monitor, and other devices

External devices that require power (e.g., monitor, printer, or speakers) also have an LED indicator to let you know if the device is on, off, or has an error.

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