LED bulbs have come along, though, and introduced the lumens rating. Lumens and watts are different, which can make it harder to figure out what type of bulb to buy.
Luckily, it's simple enough to sort out any confusion.
Why the change?
When buying an incandescent bulb, the watts rating gives consumers a good indication of how bright a bulb is. The more watts, the brighter the bulb.
The rules have changed, though. An LED that uses 60 watts is in no way comparable to an incandescent bulb that uses 60 watts. In fact, a 60-watt LED just may blind you. LEDs are designed to use less energy and naturally have a lower watt rating. This means it's useless to use watts to determine brightness.
To fix the problem, bulb companies have started using lumens to rate bulbs. This gives you a more accurate indication of how much light to expect from an LED.
Why lumens now?
Measuring in lumens isn't a new concept designed just for LEDs. It's a rating that's been used for decades as a measurement of how much light a bulb (or anything else) emits. It just hasn't been predominantly displayed on packaging until recently. In 2011, the US Federal Trade Commission started requiring manufacturers of compact fluorescent, incandescent and LED bulbs to use lumens as an indication of how bright a bulb will be.
"While watt measurements are familiar to consumers and have been featured on the front of light bulb packages for decades, watts are a measurement of energy use, not brightness," the FTC said in a press release. "As a result, reliance on watt measurements alone make it difficult for consumers to compare traditional incandescent bulbs to more efficient bulbs, such as compact fluorescents."
On packaging, the lumen rating is indicated by a number followed by "lm," the abbreviation for lumens. The higher the lumen rating, the brighter the bulb will be.
Picking the right bulb
The easiest way to figure out what bulb you need is by using an incandescent/LED conversion cart.
Say you normally use a 60-watt incandescent bulb, for example. You would probably want to choose an LED bulb that uses 8 to 12 watts and has a lumen rating of 800 to get the same illumination. This conversion chart will help you find an LED bulb similar to the incandescent you've been using:
As you can see, with LEDs, the amount of wattage you'll need varies for each lumen rating. This is because some LED brands have created bulbs that offer more lumens for less wattage. For the best energy savings, Energy Star recommends that you find a selection of bulbs with the most lumens you need, and then choose one with the lowest wattage.
Need more help picking out the perfect lights for your home? Check out our list of the Best LED Light Bulbs of 2017.
Editors' note: This article was originally published on December 2, 2015, and has been updated.