What are LEDs?

LEDs are electronic components (semiconductor diodes) that give off light when an electric current flows through them. LED stands for light-emitting diode.

How an LED makes light

An LED has a chip of semiconductor material with added impurities that form a P-N junction. When a voltage is applied across its terminals, negative charges (electrons) and positive charges (holes) meet at the junction and combine, releasing energy as light (photons). This is called electroluminescence. Less energy is lost as heat than in a filament bulb, so an LED gives more light for the same power.

Polarity

Unlike a bulb, an LED has polarity: the anode is the positive terminal and the cathode the negative one. It lights only when current flows in the right direction. On a through-hole LED the longer lead is usually the anode.

Colours

The colour depends on the materials in the chip (for example AlGaInP, GaAs, InGaN or GaP), from infrared through the visible colours (red, orange, yellow, green, cyan, blue) to ultraviolet. White LEDs usually combine a blue chip with a phosphor coating.

Advantages of LEDs

Much lower power use than incandescent, halogen, neon or fluorescent light.
Long life, commonly rated at 30,000 to 100,000 hours, so fewer replacements.
Low voltage and current (about 2–3.4 V per LED), which makes them safe to work with and easy to drive from microcontrollers.
Little heat for the light they give.
Solid state: they stand vibration and knocks.
Instant on and off, and dimmable by pulse-width modulation (PWM).
Many colours and sizes, so they fit almost any design.

How to power an LED

An LED needs a limited current. On a DC supply, put a resistor in series: R = (supply voltage − LED voltage) / current. For 12 V and a white LED (3.2 V) at 20 mA, that is 440 Ω, so a 470 Ω resistor. Our LED resistor calculator does it for one LED, a series string or parallel strings.

LED types we supply

Through-hole 5mm LEDs and 3mm LEDs; surface-mount SMD LEDs; COB LEDs; ready-made LED modules, LED strip lights and 7-segment LED digits.

Written with AI help from the specifications in our earlier catalog. Checked 11 October 2026.