The diode is flipped in each image. If the ohmmeter reads a finite resistance, that means the diode is conducting a small current in the forward direction, and the red +++ lead from the meter is touching the anode. If the resistance reads O.L (for overload), the diode is not conducting current. That means the red +++ test lead is touching the cathode.
A forward-biased diode conducts current and drops a small voltage across it, leaving most of the battery voltage dropped across the lamp. If the battery’s polarity is reversed, the diode becomes reverse-biased, and drops all of the battery’s voltage leaving none for the lamp. If we consider the diode to be a self-actuating switch (closed in the forward-bias mode and open in the reverse-bias mode), this behavior makes sense. The most substantial difference is that the diode drops a lot more voltage when conducting than the average mechanical switch (0.7 volts versus tens of millivolts).
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