How Many Watts Does a Light Bulb Use, and Why Does It Matter?

Knowing how many watts a light bulb uses may seem trivial. It’s an essential for your home, but one light bulb costs very little to operate. However, modern homes contain a multitude of light bulbs, with at least one in every room, including the shed and garage—and that multitude can add up quickly. Understanding light bulb wattage and how to reduce the power they use can drastically lower your home's energy consumption and your monthly bill. 

Light Bulb Terminology

If you’re not sure what you’re looking for, comparing different types of light bulbs can get very confusing. Lumens, temperature, watts, lifespan, and efficiency percentages can all run together, and choosing the best ones for your home becomes not much more than a guessing game. Here's what it all means. 

• Wattage measures how much electricity a bulb uses. For example, 60W incandescent bulbs use more energy than 9W LED bulbs.

• Lumens measure a light bulb's brightness or the amount of light it gives off. Large spaces require more lumens than small spaces to achieve the same light saturation.

• Temperature describes the color of light coming from a bulb, measured in degrees of kelvin (K). 2,700 K is a typical temperature for soft-white 60W incandescent bulbs. 5,000 K is close to daylight-white color. The color temperature of a light bulb doesn't significantly affect its energy consumption. 

• Watt-Hours, or Wh, expresses the amount of energy used by an appliance. To determine Wh, multiply the wattage of your light bulb by the number of hours that light is on in a day. A 7W LED bulb that runs for 3 hours per day uses 21Wh.

• Kilowatt-Hours, or kWh, is used more often to measure energy usage for your monthly electric bill. It is determined by dividing the number of watt-hours an appliance uses by 1,000. For example, that 7W LED bulb running for 3 hours per day uses 0.021 kWh daily or 0.63 kWh per month. 

How Much Electricity Do Light Bulbs Use?

The type of light bulb and its size determine how much electricity it uses. Household light bulbs consume anywhere from seven to 100 watts depending on the type, with LEDs being the most energy efficient. It's important to note that a light bulb's wattage rating is average and not an absolute amount. 

The table below shows how much energy different kinds of light bulbs require in watts to achieve the same brightness.

How Much Does It Cost to Run a Light Bulb?

While operating one light bulb for a few hours a day won't break the bank, having numerous bulbs illuminated around the house for long periods can run up energy costs quickly. Your utility company calculates your home's electricity bill using a price per kilowatt-hour. According to the U.S. Energy Information Administration, the average cost of a kWh is just over $0.11. 

The type of light bulbs you use significantly affects your monthly energy costs. Take a look at these different types that you may have in your home.

Incandescent

Incandescent light bulbs are the most costly to operate because much of their energy turns into heat instead of light. Incandescent bulbs also have the shortest lifespan of the varieties, meaning you must replace them more often. A 60W incandescent light bulb operating for eight hours per day at $0.11/kWh costs an average of $19.27 per year or about $1.61 monthly. 

Halogen

There are several types of halogen bulbs on the market. They last longer than incandescents and are more energy efficient. A halogen bulb requires around 43W to produce the same light as a 60W incandescent bulb. To run one for eight hours per day at $0.11/kWh costs $13.81 yearly and $1.15 monthly. 

Compact Fluorescent

Compact fluorescent light bulbs, or CFLs, are even more efficient and can produce light equivalent to a 60W incandescent using only 14W. The annual operating cost for eight hours per day at $0.11/kWh is $4.50 or $0.37 per month. 

LED 

LED, or Light Emitting Diode, light bulbs last a long time, produce very little heat, and use little electricity. To achieve light volumes equal to a 60W incandescent bulb, LEDs use as few as 7W. Operating one of these bulbs eight hours a day at $0.11/kWh will cost just $0.19 monthly or about $2.25 over a year. 

How to Estimate Light Bulb Operating Costs

When calculating the cost of running the lights in your house, the first thing you need to know is how much your utility company charges you per kWh. Then figure out how many lights you operate on average, their wattages, and how many hours your family has them turned on per day. 

The easiest way to do the calculations is to determine each light bulb's average kWh per day and then add up the results. Remember that some light fixtures might use more than one light bulb.

Use this formula to calculate the cost of running your individual bulbs, then add up each bulb’s cost to determine how much all the lights in your home are costing you each month. 

How to Reduce the Cost of Running Light Bulbs

The best way to reduce the cost of using your light bulbs is to switch incandescent, halogen, and CFL bulbs to LED lighting. However, replacing all of your bulbs at once could get costly, and it'll take a while for them to pay for themselves through lower energy bills. 

In the meantime, allow as much natural light into your home as possible, avoid using dark lamp shades to reduce the need for more lights, and turn off the lights when you’re not in the room. If you tend to forget to turn off the lights behind you when you go off to bed, think about installing a motion sensor instead.

If you're considering remodeling your home and looking for energy-saving ideas, talk with your local electrician about new ways to incorporate lighting into your home using LEDs.