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Energy Efficiency: Driving on LEDs

Lou Grinzo's picture

Lou Grinzo is a writer and researcher residing in Rochester, NY. He blogs at The Cost of Energy (

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  • Sep 14, 2013

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I think it’s absolutely crucial as we deal with energy and environmental issues that we recognize the interactions between pieces of systems, and between subsystems within our entire biosphere. Climate change, energy consumption, politics, economics, psychology, non-greenhouse gas pollution — it’s quite a big ball of stuff we’re trying to get our arms around and control, or at least keep from blowing up.

With this mindset, I found yet another of those “city X is saving Big Money by replacing old tech street lights with LED units” articles particularly interesting. We’ve all seen those article, thanks to the quickly rising uptake in LED street lighting. The article (blog post, actually) I stumbled across was, World’s Largest LED Streetlight Retrofit Completed In Los Angeles, which quotes a Forbes piece thusly:

Los Angeles is certainly not alone in making the switch to LED street lighting. I’ve reported at this blog, for instance, about the many other California cities, big and small, that have done the same. In March of this year, the City of Las Vegas finished outfitting 42,000 street lights with LED fixtures. One month later, the City of Austin, Texas, announced plans to install 35,000 LED street lights. And, in December of last year, CPS Energy said it would install 20,000 LED street lights in San Antonio.

But, owing to its size and influence, Los Angeles, with its partners, the Clinton Climate Initiative (CCI) and the C40 Cities Climate Leadership Group (C40), have done much to jump-start the market. Navigant (formerly Pike) Research recently predicted that shipments of LED street lights will increase from fewer than 3 million in 2012 to more than 17 million in 2020.

So, how much juice are we talking about, and what could all that suddenly available generating capacity be used for? Perhaps overnight recharging of PEVs (plug-in electric vehicles)?

Assume that each LED street light saves 88 watts over the old unit.[1]

Assume that each street light is on for 12 hours per day, on average.

That yields a savings of 1,056 watt hours per street light per night, or 1.056 kWh per fixture per night.

My Leaf S gets 4.8 miles/kWh, and I most certainly don’t drive with a light foot. Plus I’m not stingy with running air conditioning in the summer, thanks to my allergies.

Therefore, the lighting conversion frees up enough electricity to drive 5.0688 miles per fixture per night.

For Austin, that’s 177,408 miles per day, and for San Antonio it’s 101,376 miles per day.

For Los Angeles, and their 140,000 light conversion[2], that’s 709,632 miles per day.

If the projection of 17 million LED street light fixtures sold in 2020 comes true, that’s over 86 million PEV miles fueled per day from the savings. And that’s from fixtures sold in just that year, not a cumulative figure.

Now, this is the point where someone inevitably feels obligated to raise his hand and yammer on about how how the reduction in CO2 emissions per mile driven for an electric vs. gasoline vehicle is highly dependent on how the electricity is generated. And my response to all the Captain Obvious wannabes out there is:

1. Of course. Who ever said otherwise? If you find someone who does make such a ridiculous claim, my advice is to stop listening to him or her immediately.

2. Our electricity supply will get dramatically cleaner in the coming years, for the simplest possible reason: It has to. In the US in 2011, our electricity generation accounted for 41% of our CO2 emissions.[3] We can’t get close to the level of emissions cuts needed in the coming years and decades without dramatically overhauling how we push electrons down wires. And the situation is even worse in some other countries (like China and India) where their electricity generation is very coal intensive. Put another way, claiming that electric vehicles aren’t as clean as we’d like (even if they’re still cleaner than gasoline vehicles) and they won’t get cleaner is a prediction that we’ll fail to avoid very damaging, possibly catastrophic, levels of climate change impacts. That’s not a future I’m willing to sign up for.

The bottom line on all this is very simple: We’re engaged in a worldwide exercise in economics — the allocation of scarce resources — which means it is critical that we not get lost in details. The individual colored tiles on the wall might be pretty, and small clusters of them might create interesting patterns, but it’s only by taking several steps back and looking at the whole, wall-size mosaic that we can see how things fit together and, therefore, what we should be doing.

[1] I’m using the 42 watts vs. 130 watts figures from the article, LED streetlights move from pilot projects to widespread use

[2] See the Forbes article mentioned above, Los Angeles Saves Millions With LED Street Light Deployment

[3] See table ES-3 in the US EPA publication, Inventory of U.S. Greenhouse Gas Emissions and Sinks: 1990-2011.

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David Newell's picture
David Newell on Sep 16, 2013

Good article, but I am reminded..


of a city in ??upper New York??  that changed out their traffic lights for LED’s,

but it caused a huge problem, as the incandescent lights had been melting the snow, before:

and afterwards, the lights had to be retrofitted with some heating units.


maybe it’s an “urban myth”, but i am reminded by your article..



Robert Bernal's picture
Robert Bernal on Sep 17, 2013

Great post!

The leds pictured are only about as efficient as CFL’s (about 60 lm /W).

Cree is approaching 200 lm/W market and 276 in the lab!

A 12v solar panel can charge 4 lifepo4 batteries in searies, powering 4 XML’s in series, thus 10 watts can displace 28 watts of CFL. Consider that the coal to electricty efficiency is only 33%, this setup would save a total of 84 watts worth of coal (and resulting excess CO2 emissions).

The EROI on the panel is like 10, and on the battery??? (Surely, the battery would be less energy intinsive than a solar panel, right)? I read that the led acid is 2.5 x more so than li-ion (but that’s probably because it has more cycles). So, the lifepo4 is 2x that, even (because it has twice the cycles as li-ion).

WE wouldn’t have to “worry” about such drastic conservation if didn’t have to rely on the insiduous nature of our primitive energy choices. We could change all that by re-developing the molten salt reactor to power electric cars and solar manufacturing.

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