Question

How energy efficient are "Xenon" halogen bulbs in light fixtures?

Asked by Sherry
Logan, UT

Many of the light fixtures I would like to purchase for our new home say that they have halogen or "Xenon" halogen bulbs. My architect is trying to steer me away from halogens since they are not as efficient as curly bulbs. I thought I read that Xenon bulbs may be more efficient, though. We are trying to get an Energy Star rating and I can't get information about these bulbs.

Answer

David Bergman

Answered by David Bergman

New York, NY

David Bergman Architect

September 7, 2010

I love that green architects (as well as the rest of us) are becoming more knowledgeable about energy-efficient lighting -- and I’m happy, therefore, to say that your architect is correct.

  • Xenon bulbs, despite the techy-sounding name, are just a type of halogen.
  • And halogen bulbs, in turn, are basically a type of good (well, not so good) old incandescent.

The difference between standard incandescent bulbs and halogen bulbs is that the glass container surrounding the filament is filled with a halogen gas which serves to extend the life of the filament and decrease the blackening of the glass that would otherwise occur. (The blackening is tungsten from the filament accumulating on the glass as the filament wears down.) Xenon is one of a few types of halogen gas used in light bulbs; more common ones are neon, argon, and krypton.

To get to the crux of your question: halogen bulbs are indeed more energy efficient than incandescents, but only incrementally.

  • In general, filament-type bulbs have an efficacy (the industry term for efficiency) of somewhere around 10–20 lumens per watt (LPW); and
  • they are only around 5% efficient, meaning just a small amount of the electricity consumed is actually converted into light.

The majority of the electricity the bulb uses becomes heat which, of course, is not really what you’re looking for from a light fixture. Incandescent bulbs mostly fall into the lower part of that 10–20 LPW range while halogens tend toward (and sometimes exceed) the higher end of the range.

Neither of these is close to a compact fluorescent bulb, i.e. the “curly” bulb you mention. CFLs get around 40 LPW, making them 3–4 times more efficient than incandescent and 2–3 times more efficient than halogen.

Two related things to note:

  • Don’t be confused by the fact that many halogen bulbs are “low voltage.” That doesn’t mean they are more energy efficient.
  • And, if you are installing new lights and want them to count as energy efficient, a light fixture that uses regular screw-base bulbs -- even if you use a screw-base CFL -- will not cut it.

There is no such thing as an Energy Star rated fixture with that type of socket. Energy Star fixtures need to use a socket that can only accept CFLs and can’t be retrofitted with less efficient bulbs. Those lights and bulbs will have a twist-lock type socket labeled “GU-24.”

There’s lots more to be said about the differences between incandescent, halogen, and fluorescent (as well as LED), but it sounds like your architect is giving you some good advice.
 

For more information:

Read David Bergman's Q&A, "I want energy efficient lighting, but hate the cold light of fluorescents. Can you help?"

Tagged In: cfl, lighting

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