If someone from the '90s time traveled here to present day and had a look at our light bulbs, he'd know something was up. Lighting technology has evolved so much in the past few decades, it only makes sense that we need a different language to describe it.

Using a lamp's wattage to ascertain its brightness (the higher the wattage, the brighter the light), doesn't work anymore. Consumers used to be able to picture a light's brightness relative to the amount of watts it used, because there were so few light sources to choose from. The numbers were pretty standard.

However, wattage technically measures how much energy your light bulb uses, nothing about brightness. Newer sources like CFLs and LEDs produce much more light from less energy - so, we need a more accurate way to measure light output.

Enter the Lumen

A lumen is an international unit of measurement that describes the amount of light (or brightness) produced by a light source.

This scale is universal, and you can use it to measure the brightness of any light source from incandescent to LED, metal halide to fluorescent, and everything in between. The lumen scale is a concept in physics that has been around for a while, but it's only now becoming popular, as the light source pool diversifies.

It's easy to find out how many lumens a light bulb emits. As of 2011, the FTC requires a lamp's lumen output to be highlighted on its consumer packaging. Just look for it on the package's Lighting Facts Label.

As we all adjust to this scale, it might be helpful to get to know these new measurements in terms of the old ones:

• A 40-watt incandescent light bulb produces 450 lumens.
• A 60-watt incandescent light bulb produces 800 lumens.
• A 75-watt incandescent light bulb produces 1,100 lumens.
• A 100-watt incandescent light bulb produces 1,600 lumens.
• A 150-watt incandescent light bulb produces 2,600 lumens.

Of course, lumen measurements are always approximations. They can vary slightly, depending on the lamp's manufacturer, the age of the lamp, if there's dirt or dust on it, if it's clear or frosted, the lamp's voltage rating, and the exact voltage of the circuit.

Despite these marginal factors, the lumen is still the most accurate measure of your lamp's brightness.

To find the most energy-efficient light bulb to fit your exact needs, determine all the light bulbs that produce your desired number of lumens, and select the one with the lowest wattage.

References

• Never Judge A Light By Its Wattage - This blog post offers insights on the transition from using watts to using lumens.
• Shopping For Light Bulbs - Learn straight from the Federal Trade Commission why lumens are important, and what to look for when picking out a light bulb.
• Shopping For Light Bulbs (Video) - This quick video (also courtesy of the FTC) explains why we've begun using lumens to measure a light bulb's brightness.
• Lumens vs Watts - Understand the difference between lumens and watts, and discover how to use the Lighting Facts Label.
• Lumens vs Watts For LED Bulbs - The folks at Home Guides SFGate explain how to use watt and lumen measurements when selecting an LED light bulb.
• Using an article from LightingFacts.com - The experts at LightingFacts.com, a program of the U.S. DOE, teach what goes into the Lighting Facts Label, and how you can use it to find the right light bulb.
• Learn About Light Output - Lumens are especially essential for measuring light output of energy-efficient light sources. The people at ENERGY STAR explain why on this page.
• Lumens And The Lighting Facts Label - Why should you compare lumens instead of watts when buying your next light bulb? The gurus at Energy.gov illustrate the benefits of this new measurement.
• Characteristics Of Light - Here's a handy conversion chart to see how many lumens different incandescent lights produce.
• Lumens Are The New Watts - Why did we transition from using watts to using lumens? Why now? This article answers these questions, and gives a little history on the subject.