According to the California Science Center, a light bulb can work with a lemon by utilizing electrolytes within the lemon as a source of electricity. This is only enough electricity to power a small light, such as a 5 VDC bulb.
The California Science Center notes that users attempting to power a light bulb with a lemon need several supplies before starting. These include at least one lemon, zinc electrodes, copper electrodes, an LED light bulb and copper wire long enough to create a circuit. The first step of the experiment is to stick one of the zinc electrodes into a lemon to create the negative terminal.
Next, stick a copper electrode on the other side of the lemon to create the positive terminal. Make sure these electrodes are not touching. If using multiple lemons, repeat this process for all of them.
The final step is to connect the LED light bulb to both electrodes using the copper wire. The wire sticking out of the flat side of the light bulb needs to be connected to the zinc electrode, and the wire sticking out of the round side needs to be connected to the copper electrode. This creates a chemical reaction that causes electricity to gather and current to flow into the light bulb.