What is a Watt?

    Graphic of a lightbulb being held up

    Let’s say you buy a light bulb with ‘100 watts’ printed on it. And when you pay your utility bill, you can see that your energy usage is measured in kilowatt hours. The watt is obviously some unit of measurement, but what is the watt, really?

    Watt is the electrical unit for the rate at which energy is generated or consumed. So, when you turn on a lamp with a 100-watt bulb in it, it’s drawing 100 watts of electricity for every second it’s lit.

    It is important to note that when buying light bulbs that wattage does not equal brightness. This means that a 150-watt bulb is not necessarily brighter than a 50-watt bulb. This is especially important when it comes to purchasing energy-efficient bulbs like LED. Remember, a watt is the amount of energy consumed—whereas brightness is measured in lumens.

    Knowing what a watt measures, though, is only half of the story…

    Why do we call it a watt?

    All of the credit for the watt naming convention goes to the extensive research of the 19th century scientist James Watt. A fairly big name in his day, James is best remembered for his major contributions to the invention of the steam engine. Through his research, James worked to develop a different unit of measurement for ‘power’ to describe the remarkable power of the steam engine: horsepower. Watt coined the term ‘horsepower’ to measure mechanical power and to help explain the impact of his inventions in more easily understood terms. He calculated that one mill horse (an animal familiar to the people at that time) could move approximately 33,000 pounds of weight the distance of one foot per minute. This assumption of 33,000 foot-pounds per minute became the basis of measuring an item’s power in terms of ‘horsepower.’ Watt’s horsepower was adopted immediately and has withstood the test of time. In fact, even today we use horsepower to rate all manner of locomotive, automobile engines, and other machinery, and even your vacuum cleaner.

    Connecting horsepower to watts.

    There’s an interesting connection between horsepower and watts. Mechanical power is basically energy from moving machinery—like a car motor turning the tires. Well, electrical power can be considered energy from moving electrons, which is essentially the same thing: kinetic energy. And while mechanical power—measured in horsepower—is easy enough to recreate with a mill horse and some weight, electricity is a little trickier to measure with a mill horse. As time went on, using watt as an electrical unit of measurement became more common. In fact, when Thomas Edison invented the first reliable light bulb in 1879, the British Science Association (a charity that invests in supporting and strengthening scientific initiatives), determined that James Watt’s namesake was the most suitable unit of measurement.

    Here are a few more facts about the watt for you:

    • A ‘kilowatt’ is a unit of power equal to 1,000 watts
    • A ‘kilowatt hour’ describes the amount of energy used to provide 1 kilowatt of power over the course of 1 hour
    • 1 horsepower equals 746 watts

    Pretty interesting? We think so too.

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