The Answer
The Short Answer
Wattage was once used as shorthand for familiar incandescent outputs, but it is not a unit of brightness. Modern lamps can produce the same lumens with different wattages. Read both values on the label: lumens for output, watts for power, and lumens per watt when comparing efficacy.
The Full Explanation
Use Replacement Equivalents Carefully
ENERGY STAR lists minimum outputs of about 450, 800, 1,100, and 1,600 lumens for traditional 40W, 60W, 75W, and 100W incandescent replacements. The wattage needed to reach those outputs varies by the new lamp, so check its actual label rather than assuming one LED conversion.
Watts and Efficacy
Watts remain useful for estimating electricity use. Dividing lumens by watts gives source efficacy, but a highly efficient lamp can still be unsuitable if its distribution, colour, glare, fitting, or dimming behaviour does not match the application.
How to Shop in Practice
For a like-for-like replacement, start with the familiar lamp's lumen equivalent. For a new layout, consider where the light must land and how the fitting distributes it. Compare actual watts only after candidate products meet the output and quality requirements.
Related Questions
Sources
- 1Learn About Brightness
ENERGY STAR
- 2Purchasing Energy-Efficient Light Bulbs
U.S. Department of Energy