Question

What is the greenest dimming light bulb?

Asked by Doug Lanning
Phoenix, AZ

The light bulb I found has unbalanced light and flickers.

Answer

David Bergman

Answered by David Bergman

New York, NY

David Bergman Architect

January 25, 2011

The greenest light bulb? That’s an easy one -- that’d be the sun.  Oh wait, global warming’s heat source is the sun. Maybe it’s not such an easy question.

Actually, it sounds like you’re asking a couple of intertwined questions:

  • What are energy-efficient light sources, and
  • which ones are good at dimming.

And I’m guessing from your description of unbalanced and flickering light that your solution to those two questions was getting a dimmable CFL. At least that’s what my experience has largely been.

Let’s look at the choices

Sunlight. Cheap (free, actually) and doesn’t use non-renewable resources. Dimmable? Not directly, but curtains and blinds do a pretty good job. What’s not to like? That’d be the hours between sunset and sunrise.

Candles. When we dim lights, we’re often trying to mimic soft romantic candlelight. (Never mind that candles do flicker.) Problem is, candles are not all that green in terms of the resources used and pollutants emitted for the amount of light generated.

Incandescent light bulbs, or "toasters," as I often refer to them. (Before anyone jumps on me, I’m geek enough to know that "toasters" are also the derogatory nickname for the bad guys on Battlestar Galactica.)

  • The good news: they dim really nicely.
  • The other good news: they use less energy as you dim them.
  • The bad news: they’re still better at making heat than light. About 10% of the electricity consumed is converted into light; the rest becomes heat.

Fluorescent light bulbs. Yes, we know they’re much more energy-efficient (about 4 times) than incandescents. And we know they aren’t the bad old noisy, pallid lights from the basement rec rooms and school libraries of the '60s and '70s.

But, and here’s the kicker, they don’t like to be dimmed. In fact, many of them just plain won’t do it.

  • You can get dimmable CFLs to replace an incandescent bulb, but don’t expect them to make the room all romantic, or to not momentarily blind you when you turn on the bathroom light in the middle of the night.
  • They have to start at full intensity and then will only dim down a bit before either shutting off or, worse, strobing.
  • Even the more expensive lights that use separate dimming ballasts will not do the job nearly as nicely or fluidly as an incandescent bulb. (The ballast may claim to dim down to 5% or 10%, but that’s not 5% or 10% of the light output.)

So where does that leave us? 

There are two other solutions that I know of:

1. Multiple light sources. For a kitchen I designed a few years ago, we didn’t have the budget to buy dimming fluorescents so I dispersed the recessed lights on two separately switchable circuits.

  • You could turn on either or both, depending on how much light you wanted.
  • You can achieve the same kind of flexibility by employing multiple types of lighting: ceiling, wall, table, etc.

2. So you want lighting that’s energy-efficient AND dimmable? We can do that so long as you don’t want inexpensive or very intense.

LEDs (light emitting diodes, for those whose technological knowledge stops at VCRs) are becoming very energy-efficient and have the potential to become even more so as the tech evolves. And many LEDs (not all!) are dimmable, as in dimmable the way incandescents are. 

The hitches are:

  • they are significantly more expensive upfront (though you’ll make up the cost down the line in your lower energy bills and much longer bulb life) and
  • the bulbs that are currently available to replace your incandescents only achieve lumen intensities equivalent to the 60 watt energy hogs.

Both hitches will loosen, roughly according to Moore’s law. LEDs are getting brighter and cheaper all the time. LED bulbs that were $100 just last year and only available from specialty sources can be found for $40 now at places like Home Depot. And their color rendition is getting really good, too.

Consider this

It’s worth asking, by the way, if you will really use dimmers if they are available.

Think about how you and others use -- or don't use -- the ones you have. In my unscientific observations, most dimmers are either left on full or set once, never to be moved again.

So, while we have some available and almost-great answers, none of them (yet) are ideal.

 

For more information:

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

Also, read David's answer to the question "How energy efficient are "Xenon" halogen bulbs in light fixtures?"

Tagged In: cfl, lighting, led

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