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Watts vs. Lumens: Understanding the Difference

July 6, 2021

Setting Straight Lighting’s Most Common Mistake

When shopping for a bulb, it is common to ask yourself how bright you’d like the bulb to be. Make sure you’re looking at the right form of measurement. 

A watt is a unit of power, measuring the amount of energy (joule) that is used over a period of time (second).  

For our purposes, when talking about bulbs, a watt measures how much electricity the bulb requires per second. This is not an indicator of how bright the bulb is, necessarily. 

If you are looking to determine how much light a bulb will provide, look to lumens, not watts. A lumen is the direct measurement of light output. The amount of lumens can tell you the degree of brightness, regardless of whether it is emitted from an incandescent, halogen, or energy-efficient LED bulb. 

A handy trick

Want to know how efficient your bulb is at giving you the light you need? Look to how many lumens you get for each watt. 

Guide to Shopping for Bulbs

To ensure the room is bright enough, do a few simple calculations.

1. Measure the area you would like to illuminate. What is the square footage?

  • If illuminating a floor, ~20 lumens/ft²
  • If illuminating a table, ~30 lumens/ft²
  • If illuminating for task lighting/desk, ~50 lumens/ft²

2. Choose your bulb type.  LED or Incandescent?

  • Standard 60 W Incandescent Bulb = 480 lumens
  • Standard 9 W LED Bulb = 800 lumens

3. Last but not least. Calculate the number of bulbs you’ll need.

  • For LEDs: (ft² of room x lumens needed for illumination type)/800 = # bulbs
  • For Incandescents: (ft² of room x lumens needed for illumination type)/480 = # bulbs

Happy Shopping.