Understanding Watts vs. Lumens for Home Lighting

There have been some major changes in lighting in recent years due to the introduction of energy efficient CFL and LED bulbs. Familiar old incandescent bulbs are becoming a thing of the past, as both their energy-hogging habits and their “wattage” rating become obsolete. In their places will be high efficiency bulbs with a much more accurate “lumens” rating. Here’s a handy guide to help you understand the difference and navigate the changes.

Watts vs. Lumens

To start with, what’s the difference between a watt and a lumen?

Watts:

Watts are a measurement of how much electricity something uses. It actually has nothing to do with how bright a bulb is, but incandescent bulbs are so similar that when we bought a 100-watt incandescent light bulb, we had a general idea of how bright it would be.

With newer types of bulbs, it takes far fewer watts to create just as much light, so wattage ratings are no longer very useful. Each type of bulb is different, and the whole idea is to develop bulbs that use fewer watts to make more light.

Lumens:

Lumens, on the other hand, actually measure the amount of light being put out by the bulb. Lumens are a much more accurate measurement, because it tells you how the light actually performs, regardless of the source that produced it.

One lumen is approximately equal to the amount of light put out by one birthday candle that’s one foot away from you. To help you get an idea of the lumen scale, a standard 60-watt bulb puts out around 750-850 lumens of light. If you’re choosing bulbs for task lighting, look for bulbs with 1000 lumens or more.

Lumens Per Watt Rating

Like miles-per-gallon in a car, the lumens-per-watt rating measures how much light that particular bulb produces per watt of power used, which tells you how energy efficient it is. Under the new system, when shopping for a light bulb, you should first look for the bulbs that produce the number of lumens you need.

Once you know the right brightness, you can then look at the lumens-per-watt rating to find the bulb that’s most energy efficient. The lumens-per-watt rating is an average, since light bulbs become less efficient as they age.

Energy Star Bulbs

If you’re not into fine print, one easy way to choose light bulbs is to look for the Energy Star rating. To qualify for Energy Star, light bulbs must meet certain lumens-per-watt standards. Here’s a handy chart to help you understand how watts and lumens relate to each other under the Energy Star system:

Further Information

• CFL Bulbs: A Bright Idea for Going Green (article)
• LED Lighting 101 (article)
• Learn About Light Output (energystar.gov)
• Energy Independence and Security Act of 2007 (U.S. Senate)