Q: What is the difference between watts and lumens?
Daylight Savings has arrived and the days are shorter and darker. This time of year we are all spending more time inside and looking to our lighting to keep things bright and chase away the darkness.
As lighting technology has become more efficient there has been a shift in terminology that can leave many consumers at a loss when selecting new bulbs and fixtures. In the days of the incandescent bulb it was common to select and discuss lights by the watts (actually Watt Hours) but new LED bulbs are more likely to refer to a lumen rating for output.
Watts: Measures of Usage
Skipping a full physics explanation, many of the modern terms used to describe power usage originated during the industrial revolution as the world started to define relationships between power and time/output. The term watt was named after Scottish inventor James Watt. (He also coined the term horsepower in an effort to describe the power created by his improved steam engines to the public.)
In simple terms a watt is simply a measure of power produced. For electric light bulbs the term watts is commonly used to describe watt-hours (Wh) or the amount of energy used to power the bulb for an hour.
Cost was important:
As indoor electricity became commonplace, the cost of electricity was significantly higher than today so it made sense to discuss lights in terms of the energy or costs incurred.
For the consumer in 1880, the cost to run a 100Wh bulb for an hour was the equivalent of 3 hours of work, whereas today it is only seconds of labor for the same hour. (Reference: Statista.com)
Lumens: Measures of Output
As modern lighting has become more efficient the terminology is changing to focus more on measures of output than power usage. Here enters the lumen. Instead of a measure of cost a lumen is a measure of output of visible light.
LED lighting today us roughly 7 times more efficient than incandescent bulbs so manufacturer’s are shifting their focus and labeling bulbs to reflect the amount of light produced rather than energy consumed. In addition modern LED bulbs last longer than traditional incandescent bulbs.
LED bulbs are simply more efficient at producing light/lumens with the same watt usage than incandescent, halogen or CFL bulbs. An incandescent bulb produces about 12-18 lumens per watt while modern LED can range anywhere from 75-100 lumens per watt depending on manufacturer and quality of the technology.
Determining Lumen Requirements:
A simple chart or online calculator may be the easiest way to determine lumen requirements if you are replacing a single bulb that you are satisfied with. For more detailed lighting projects or upgrades to overall design you may want to look at the purpose of the room and/or fixture.
Factors like square footage, room or fixture purpose as well as color range of the light emitted can have a big impact on selecting a light fixture.
What’s Next:
Once you understand the basics of lumen output and have determined your needs it’s important to look at the color range and type of lighting you would like to have. We will talk about that next - stay tuned!
Ask the Electrician is a column we publish with our advertising partner WCHL/Chapelboro. In “Ask The Electrician,” Scott answers common questions about electrical work, from switches and outlets to safety issues and preventative maintenance. If you have a suggested question for us to answer – or need an electrician – please reach out to our office.
See the article on Chapelboro.com: Lighting Watts and Lumens