Why does the measured current differ from the calculated current in this circuit?
$$I=\dfrac{V_{CC}-V_{F}}{R} = \dfrac{5V-1.8V}{330\Omega} = 9.7 mA$$ As example the LED forward voltage drop is 1.8V.

An easier approach is to calculate the required resistance:

$$R=\dfrac{V_{CC}-V_{F}}{I_F}$$
For example: I have orange LED and I want 10 mA current through: If=10ma -> Vf=1.7V


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