PAGE 016 OF 150 · COLOURS, SIZES & TYPES
Red LEDs
Red LEDs usually have the lowest forward voltage of the visible colours.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
About red LEDs
Red was the first practical visible LED colour and is still the most common. Red chips are made from aluminium gallium indium phosphide or similar materials and emit at roughly 620 to 630 nm.
Electrical and practical details
- Forward voltage is typically 1.8 to 2.2 V at 20 mA.
- They run well from a 3 V cell or 5 V supply with a resistor.
- Red is easy to see in daylight and is widely used for power, standby and warning lights.
- Red light disturbs night vision least, so it is used in torches for astronomy and cockpits.
Tip
Because red has the lowest forward voltage of the visible colours, it is the easiest to light from weak supplies and a good first LED for testing a circuit.
REMEMBER
Colour is set by the semiconductor material, not by the plastic lens.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.
Explore LED clocks, stopwatches and electronics at cosycom.com.