Light Thoughts

I have fielded a variety of questions from people trying to figure out what kind of lighting is more or less efficient than others. Many people understand that lower wattage is better, from a consumption view, but they don’t necessarily feel like they are comparing apples to apples when they try to compare incandescent to compact fluorescent or LED.

The way to determine efficiency of any given source is to figure out how much light you get for the amount of power used. Using the lowest wattage source may not be the most efficient approach if it doesn’t give you enough light and you end up adding more. The lighting industry uses a measurement called Lumens per Watt, or LPW. We take the total lumen output of the source divided by the wattage so we can make direct comparisons.

For example: a regular 100 watt light bulb for a table lamp, with clear glass so you can see through it, will provide about 1,750 lumens (it will say this somewhere on the box). Since it uses 100 watts, you divide 1,750 by 100 and figure out its efficiency is 17.5 LPW. Now you can compare that to a compact fluorescent replacement lamp (with a screw in base for your lamp) and find that it provides about 1,700 lumens for only 26 watts. The CFL lamp has an efficiency of a bit over 65 LPW. Therefore, we can say that the CFL lamp is almost 4 times as efficient as the incandescent.

To provide some general guidance I’ll type up a quick list of some sources and their LPW ranges:

• Standard incandescent bulbs range from around 4 to 20 LPW
• Tungsten-halogen bulbs range from around 18 to 22 LPW
• Low wattage compact fluorescents range from around 20 to 60 LPW.
• High wattage compact fluorescents range from around 50 to 80 LPW.
• Linear fluorescents range from around 65 to 95 LPW.
• LEDs range from around 5 to 40 LPW, although there is so much development of LED sources right now this range is likely to change quickly.

As with everything I write about lighting, there are some caveats. I’ll discuss a few of those in upcoming posts.

Tags: efficiency, fluorescents, incandescents, light bulbs

This entry was posted on Wednesday, July 8th, 2009 at 3:34 pm and is filed under Fluorescent (and CFL), General Knowledge, Homeowner Tips, Incandescent, New Tech. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.