# How much water power do you need to turn on a light bulb? How much wind power do…

#### How much water power do you need to turn on a light bulb? How much wind power does it take to turn on a light bulb? Can artificial light make a solar paneled car run? If so, how bright? — BB, Stafford Springs, CT

If you are trying to light a 60 watt bulb, you must deliver 60 watts of electric power to it (unless you are willing to have it glow relatively dimly). So the answers to your questions are 60 watts of waterpower and 60 watts of windpower. But you are probably more interested in how much water or wind is needed to run those power sources. An efficient water generator that produces 60 watts of power lowers about 6 liters (or one and a half gallons) of water about 1 meter (or 3 feet) each second. An efficient wind generator that produces 60 watts of power stops about 1 cubic meter (or 32 cubic feet) of air moving at 36 km/h (or 21 mph) each second. Finally, a solar powered vehicle needs at least several hundred watts of power to operate. Since solar panels are only about 20% energy efficient and artificial light sources are also only about 10 to 50% energy efficient, it would take thousands of watts of artificial lighting to operate a solar powered car. Not very practical.