The life cycle of a lightbulb

I have now switched all the light bulbs in my life from incan­des­cents to CFLs — com­pact flu­o­res­cent lights. The ini­tial moti­va­tion was cost: while a single CFL bulb is a lot more expen­sive than an incan­des­cent, it can last 10 to 25 times longer and saves a lot of money in the long run (not to men­tion the fact that I’m short and don’t like changing light bulbs).

This is a trade-​​off: more money now for less money later. Civil and envi­ron­mental engi­neering pro­fessor Matthew Eck­elman devotes his life to trade­offs, not just of the finan­cial sort, but of the entire life cycle sort.

When we talk about “going green” and being “sus­tain­able,” it’s not as simple as buying an organic cotton tee shirt or switching from incan­des­cents to CFLs. We have to look at the bigger pic­ture in its entirety, said Eck­elman, who joined the North­eastern fac­ulty in January.

The models I use are envi­ron­mental life cycle assess­ment models,” said Eck­elman. “Our overall goal is to pro­vide policy– and consumer-​​relevant infor­ma­tion about the envi­ron­mental impacts of dif­ferent prod­ucts and materials.”

In the late 2000s, CFLs were a big thing, Eck­elman said. Wal­mart sold over 100 mil­lion bulbs in a single year. As the bulbs became more preva­lent, people began to learn that each one con­tained about a bit less than 5 mg of mer­cury — a toxic chem­ical we’ve all been warned about again and again. That’s 675 kg of mer­cury from Wal­mart alone in one year. Clearly these things must be bad for the environment…right?

Well, the story isn’t that simple. As a grad­uate stu­dent at Yale Uni­ver­sity, Eck­elman pub­lished a study showing how com­pli­cated it really is. “When you trade out an incan­des­cent for a flu­o­res­cent bulb,” said Eck­elman, “you intro­duce mer­cury in the bulb. On the other hand, you use less energy. The largest source of mer­cury emis­sions in this country is coal fired power plants.”

Using a com­pu­ta­tional mod­eling approach, Eck­elman and his team ana­lyzed all 50 states and 130 coun­tries, looking at the energy use sav­ings of CFLs, the char­ac­ter­is­tics of local elec­tric power and CFL recy­cling rates in every juris­dic­tion for which they had data.

What we found is that it depends on where you are,” he said. In Cal­i­fornia, for example, it doesn’t make sense to use CFLs from a mer­cury per­spec­tive, because Cal­i­fornia doesn’t have many coal fired power plants. The mer­cury con­tent intro­duced in the bulbs out­weighs that elim­i­nated by the energy savings.

In China, though, coal-​​fired power gen­er­a­tion is the dom­i­nant energy pro­duc­tion prac­tice and that (at least at the time of the study), very few facil­i­ties had pol­lu­tion con­trol equip­ment that cap­tured mer­cury, so emis­sions there were very high.

Then again, the CFLs used in china have a higher mer­cury con­tent than here and Cal­i­fornia imports a lot of its power from Nevada, which does use coal plants. “It’s always a tradeoff one way or another,” said Eck­elman. He uses mod­eling to under­stand and quan­tify the effects of those trade offs. His work can then help con­sumers like you and I make better buying deci­sions and inform policy makers about the big picture.

The loca­tional depen­dence of the CFL analysis is not unique: “This is a gen­eral fea­ture of a lot of these life cycle studies,” said Eck­elman. So informing and engaging local gov­ern­ments about their par­tic­ular sit­u­a­tion is extremely important.

Photo: kevgee, “Broken Light­bulb II” Feb­ruary 7, 2009 via Flickr. Cre­ative Com­mons attribution.