How many lemons light up a LED?

The number of lemons needed to light up an LED depends on the type of LED and the voltage it requires. Typically, a single lemon can produce about 0.5 to 0.9 volts, so at least 2 to 3 lemons connected in series may be needed to generate enough voltage (around 2 volts) to power a standard LED. However, the exact number can vary based on the lemon's acidity and size.