How to Measure Electrical Power of Light Bulbs

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Measuring electrical power of light bulbs can be done in different ways to find the amount of power a device uses. Most store bought appliances have a label indicating the amount of power that particular device uses. To get a more accurate value, two of three things must be known. They are the voltage across the device, the current used by the device and the resistance of the device. Power is equal to voltage times current; voltage squared divided by the resistance; and current squared times the resistance.


How to Measure Electrical Power of Light Bulbs

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Measuring electrical power of light bulbs can be done in different ways to find the amount of power a device uses. Most store bought appliances have a label indicating the amount of power that particular device uses. To get a more accurate value, two of three things must be known. They are the voltage across the device, the current used by the device and the resistance of the device. Power is equal to voltage times current; voltage squared divided by the resistance; and current squared times the resistance.


Screw the light bulb into the light bulb holder and plug the light bulb holder cord into an outlet. Turn the multimeter on and set it to measure 0 to 500 volts AC. Take one probe from the multimeter and touch it on one of the light bulb terminals. Do not touch the terminals with your hands. Take the second probe and touch the second light bulb terminal. The multimeter should read between 110 and 120 volts. An example would be 115 volts.


Write down the reading and unplug the light bulb holder. Change the setting on the multimeter to read current. This is usually the 10A setting. On some meters , one of the probes has to be moved to a different slot on the meter.


Unscrew one of the light bulb terminals and disconnect one of the wires that feed the light bulb holder. Connect the removed wire to one of the probes, and connect the other probe to the vacant light bulb terminal of the light bulb holder.


Plug the light bulb holder back into the outlet. The multimeter should produce a current reading. An example would be 1.5 amps. Unplug the light bulb holder and disconnect the multimeter.


Take the readings and multiply them together. Using the examples would mean 115 volts times 1.5 amps equals 172.5 watts. Watts is a unit of power.


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