A typical red light-emitting diode has a minimum forward voltage of approximately 1.75 volts. Below this voltage no current flows through the LED. Eine typische rote Leuchtdiode hat eine
As a result, you can accommodate a maximum of five LEDs in a series circuit. In that case, each LED stands 1.8 volts. This is enough for a weak forward current and a faint glow. You can even do without the current-limiting resistor.
If you connect six LEDs in a series circuit, each LED stands only 1.5 volts, below the minimum forward voltage. All LEDs remain dark.
The next experiment shows you how you can still connect six LEDs.