PAGE 017 OF 150 · COLOURS, SIZES & TYPES
Green LEDs
Green LEDs generally need a little more voltage than red ones.
LED SYMBOLTriangle points from anode to cathode; the arrows show light leaving the part.
Two kinds of green
Older yellow-green LEDs use gallium phosphide and emit near 565 nm with a forward voltage around 2.1 V. Modern pure green LEDs use indium gallium nitride, emit around 520 to 530 nm and need about 3.0 to 3.4 V.
Why green looks bright
The human eye is most sensitive near 555 nm, so a green LED appears brighter than a red or blue one at the same power.
Practical points
- Check the datasheet before choosing a resistor, since the two types differ by about a volt.
- Pure green LEDs will not light from a 3 V coin cell reliably.
- Green is the usual colour for ready, OK and running indicators.
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.