PAGE 009 OF 150 · LED BASICS
Forward Current Basics
Typical indicator LEDs run near 10 to 20 mA.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
Current makes the light
Forward current (If) is the current through a lit LED, and brightness rises roughly in step with it. This is why you design around current and not voltage.
Common figures
- Standard 3 mm and 5 mm indicator LEDs: about 20 mA continuous maximum.
- A sensible working value: 5 to 15 mA, which is bright enough indoors and kinder to the part.
- High-power LEDs: hundreds of milliamps to several amps, always with a proper driver and heat sink.
Limits to respect
The datasheet's absolute maximum current is a ceiling, not a target. Running at it produces more heat, shortens life and gradually dims the LED. Pulsed ratings are higher, but only for very short pulses.
Reading your circuit
Use a series resistor to set the current, then confirm with a multimeter in series with the LED if you need to be sure.
REMEMBER
An LED is a diode, so current flows through it in one direction only.Try it yourself
Sketch the circuit on paper first, calculate the values, then build it on a solderless breadboard using a low-voltage supply. Measure with a multimeter before you make anything permanent.
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