Do you have a bad habit of leaving the lights on in empty rooms? Do you ever wonder how much it’s costing you? The answer can depend a lot on what kind of light Bulbs you’re using.

While incandescent light bulbs were the standard for decades, there have been major advances in lighting technology in recent years. First came CFL bulbs — the swirly ones that look like ice cream cones — followed a few years later by LED bulbs, which many people are upgrading to today. Both Bulb styles were pricey when they first came to market, but prices have come down enough that they’re now the best overall value despite being more expensive than incandescent bulbs.

There are two reasons for this: Energy efficiency and longer bulb life. If you’re used to using 60-watt incandescent bulbs, you can maintain the same light levels with CFL bulbs that draw 13 to 20 watts, or LED bulbs that draw 6 to 12 watts. Making the switch can reduce the lighting portion of your electric bill by more than 80 percent.

You’ll also replace these bulbs a lot less often. A typical incandescent bulb will glow for about 1,000 hours, but CFLs last about 10,000 hours and LEDs can hang in there for 25,000 hours or more.

How Much Energy Does a Light Bulb Use Per Hour?

As energy calculations go, this one’s easy. To find the energy usage of a light bulb and how much it will cost you, all the information you need is printed right on your light bulbs and your electric bill. First, check your light bulb’s wattage, which has a “W” at the end. This may be printed on plastic or stamped into metal. Next, check the kilowatt-hour (kWh) rate on your latest electric bill. This is the rate you pay for each kilowatt-hour of electricity.

Divide the bulb’s wattage by 1,000 to convert it to kilowatts. Then, multiply the bulb’s kilowatts by your kWh rate to see how much the bulb will cost you per hour.

Let’s assume your kWh rate is 12 cents and you have a 60-watt incandescent bulb. You want to calculate your 60-watt light bulb energy use and cost per hour.

• 60 watts multiplied by one hour is 60 watt-hours of energy. Divide by 1,000 to get .06 kWh. 
• .06 kWh multiplied by .12 cents is .0072 cents. 

So how much does it cost to run a 60-watt light bulb for 1 hour? A little more than 7/10ths of a penny at this rate. That may not sound like much, but remember, that’s just one bulb glowing for one hour. A house full of lights can add up by the end of the day.

But what if you also had an equivalent LED bulb that only uses 12 watts? 12 divided by 1,000 is .012, and .012 multiplied by .12 is .00144. At your 12-cent energy rate, you could use that 60-watt incandescent bulb for about 140 hours before it cost you a dollar, but that same dollar could keep the 12-watt LED bulb burning for nearly 700 hours.

Light Bulb Wattages vs. Lumens

When incandescent bulbs dominated the market, shoppers looked to wattages to determine bulb brightness. The higher the wattage, the brighter the bulb. That’s still true for the modern bulbs of today, but the relationship between the wattage and brightness is much different for energy-efficient bulbs. And to help consumers make sure they’re buying the bulbs they want, manufacturers now make a point of labeling their products’ lumen counts.

Unlike wattages, which are measurements of energy, lumens are measurements of light. A 60-watt incandescent light bulb produces about 800 lumens of light, the same as a roughly 15-watt CFL or 8-watt LED. If you’re planning on investing in energy-efficient light bulbs, it’s helpful to familiarize yourself with the lumen equivalents of the incandescent bulb wattages by reviewing a conversion chart. And when making purchases, look for the lumen count, abbreviated on bulbs and packaging as “lm”.

It’s still a good idea to turn off the lights when you leave the room. But if you’re still using old-fashioned incandescents, the most important thing you can do to slash your lighting budget is invest in some long-lasting energy efficient bulbs. They’ll pay for themselves.