Lumens and LEDs That Use Them Explained


All right, I lied. I really can't give you a simple answer to the meaning of life, but if you're looking for a simple explanation of how a lumen is used to measure lights, and why LED lamps are the most efficient way of producing high light output, you've come to the right place. Describing the measurement of light is, by nature, a complex thing. In order to understand what a lumen actually measures, you need to understand a little about how light has been measured historically.

Lumens

The technical definition of lumen is this: A lumen is the standard measurement for a unit of luminous flux, a measure of the perceived power of light. Unlike radiant flux, which measures the total amount of light energy put out by a light source, luminous flux measures the amount of light that can be perceived by the human eye. Let's look at a concrete example to help make that clearer.

Imagine that you are standing in the center of a sphere with a radius of 1 meter. You are holding a birthday candle. Take a square of cardboard that measures 1 meter on all sides and put it against the wall of the sphere so that the edges rest against the wall. One lumen is the amount of light that falls on that square of cardboard. The more candles you light at the center of the sphere, the more lumens you are shining on the cardboard, and the brighter the light is.

But how does that translate to the lighting measurements that we're used to? Most people are familiar with incandescent light bulbs that are measured in watts. While it seems to make sense that the higher wattage you use, the brighter the light you get, it's not really the way that it works. That's because watts and lumens measure two very different things. A watt is a unit of electrical energy - in other words, input. A lumen is a measure of light intensity - output. More simply - a light bulb uses watts to make lumens.

A standard 100 watt incandescent light bulb uses 100 watts of power to put out about 1500-1700 lumens, or about 17 lumens per watt (17 lm/w). We've known for quite a long time that it's not a very efficient way to make light. By contrast, compact fluorescent lamps (CFLs), which are the most common replacement for incandescent bulbs, put out 35 to 60 lumens per watt. That means that you can get the same amount of light for one half to one quarter of the power spent. LED (light-emitting diode) lamps offer even more lighting efficiency. There are already manufacturer making LED lamps that put out 100 lumens per watt, and the U.S. Department of Energy is on track with an energy plan that calls for LEDs that put out 160 lumens per watt by 2025.

Currently, LED lamps and lighting are still considered too expensive for typical home lighting - but that's not the case in flashlights and portable lights. In fact, LED lamps really shine when it comes to flashlights.

- LED lamps are brighter than incandescent bulbs. LED lamps have been measured at up to 60 times brighter than filament bulbs that draw the same amount of power.

- LED lamps last longer than filament bulbs. And we're talking exponentially longer. An LED lamp for your flashlight could conceivably last up to 10,000 hours.

- LED lamps use less power, so batteries last 2 to 10 times longer.

Your flashlight is the one piece of emergency equipment on which you should be able to depend - it only makes sense to choose a flashlight with an LED lamp that's brighter, more dependable and longer lasting.

~ Ben Anton, 2008

 


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