An LED is a small light that runs from a low DC voltage. It only lights when current flows one way through it, so it has to go in the right way round, and it needs a resistor in series to set its current. This is a standard 3mm round-top through-hole LED with short legs, a water-clear lens and a cool white light. The clear lens looks colourless when off and throws a bright, focused beam when on, far brighter than a coloured indicator at the same current. For coloured 3mm LEDs with tinted lenses, see the 3mm diffused LEDs in red, orange, yellow, green and blue.
Use it for power and status lights, a small lamp in a model, or a light behind a panel in a 3mm hole. The 2.54mm lead spacing plugs straight into a breadboard and fits standard 0.1 inch PCB pads. White needs about 3V itself, so it is brightest from 5V; on a 3.3V pin it still works with a small resistor but glows softer. Sold singly with a minimum of 10. Each LED needs its own resistor, which is not included; the 600-piece resistor kit has every value given below. For a bigger lens, see the 5mm water-clear LEDs.
Specifications
Datasheets
Wiring & getting started
- Find the positive lead
The longer lead is the anode (+). The shorter lead is the cathode (-), and the rim has a small flat on that side. If you trim the leads, the flat still tells you which is which.
- Pick the resistor
Use one resistor for each LED: 220 ohm on 5V or 1k on 12V runs it at about 8 to 10mA. On 3.3V there is little voltage to spare, so use 47 ohm and expect a softer glow (about 2 to 6mA). If it is too bright for an indicator, a 1k resistor on 5V gives a gentle glow at about 2mA.
- Wire it up
Connect the supply positive, or a board output pin, to the resistor, the resistor to the long lead, and the short lead to GND. The resistor can sit on either side of the LED as long as it is in series. On a breadboard the LED and resistor push straight in; on a PCB, solder each lead for about 3 seconds and trim the ends.
- Check it works
Switch on and the LED lights white. If it stays dark, it is almost always in backwards: switch off, turn it round and try again.