How many lemons does it take to power a light bulb?

The average lemon produces about 0.7 volts of electricity with a current of one mA (0.001 Amps), generating a total power flow of about 0.0007 watts. That means in order to power a 15w compact fluorescent light bulb it would require approximately 21,459 lemons wired together properly.

Voltage is the difference in electrical charge between two points, current, measured in Amps, is the rate at which charge flows, and power is the product of these two (that is the product of, voltage times current). The extremely low Amperage of lemons is the reason that, despite creating a decent amount of electrical charge, it would take an obscene amount to generate any significant amount of power.