LED (wiring diagram)

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The current passing a light emitting diode must be restricted by a resistor in series connection. The yellow, green and red LEDs need 2 V, the blue ones 3 V. The electrical circuit on the top can be operated by a 12V-power supply. In this case a 1 kOhm-resistor is acceptable. Less than 1 kOhm damages the LED, more reduces the luminous power.
A (LED) diode can be verified by attaching it to an ohmmeter. In one direction there is a certain resistance, whereas the other blocks.