From watts to lumens — watt’s that?

Jun 30, 2023

Aug. 1 was the end of an era. The age of Thomas Edison’s electric light bulb, patented in the late 1800s, is over. Under the new energy efficiency rules, stores can no longer sell incandescent lights. LEDs (light-emitting diodes) are taking their place.

We are used to measuring our light bulb intensity in watts. Improvements in energy and power usage have caused wattage to become irrelevant when trying to determine brightness. We now need to learn our lumens. What is a lumen? The Merriam-Webster dictionary defines a lumen as “a unit of luminous flux equal to the light emitted in a unit solid angle by a uniform point source of one candle intensity.” Simply put, a lumen is a measure of visible light.

Wattage also is a measurement, but instead of measuring the light produced, it measures the amount of electrical power the light bulb consumes. Lumens measure the actual brightness, regardless of how much power is needed. Conventional logic dictated that a bulb with a higher wattage would produce a brighter light. This is not the case today. Scientific advances in modern lighting allow us to produce more light using less energy. For example, a 23-watt LED can produce the same amount of light (lumens) as a 100-watt incandescent bulb. According to an energy economist at the University of California, going from an incandescent light to an LED is like replacing a car that gets 25 miles to the gallon with another one that gets 130 mpg. And technology will continue to improve!

The advantages are many. When LEDs first entered the marketplace, they were considered pricey; now the cost is in parity with incandescent lights. The Department of Energy expects Americans to collectively save $3 billion a year on utility bills by using LED bulbs! Over time, the energy department projects the new rules will cut carbon dioxide emissions in the millions of metric tons.

LEDs have more immediate and practical benefits. Homeowners can expect fewer trips to the store to purchase lightbulbs, and less teetering and falling from ladders trying to replace them because LED light bulbs last approximately 25 to 50 times longer than their incandescent counterparts.

This information on the new lighting measurements is also important when choosing outdoor residential lighting. A guideline would be 50 lumens for garden lights, 100 lumens for path and landscape lights, 120 lumens for lanterns, and 700 lumens for security flood lights. These levels of lumens will not interfere with nocturnal wildlife, will not interfere with the 80% of birds that migrate at night, will provide enough light and security, will save energy, and will respect your neighbors’ right to a night sky without trespass.

As improvements in energy and power have improved, wattage has become outdated in determining the brightness of a light. Wattage never did a good job of measuring brightness; it was just a guess based on power usage. We are now using energy and power in a smarter and more efficient way. We must now become accustomed to measuring light based on actual units of visible light.

Watts off, lumens on!

For more information, visit energy.gov/new-energy-efficiency-standards-lightbulbs or homedepot.com/c/ab/how-many-lumens-needed-outdoor-lighting

Katherine Webster is a Dark Sky member and a Lights Out Colorado volunteer.