Cool, $150,000 per year is pretty good. Thanks for the update.

Over the course of 6 years since this article was posted, Ann Arbor has converted more than twice as many street lights as the article mentions. The payback time is listed as four years, which is pretty close to the 3.8 projected here in 2008. They say that the 223 lights they are converting this year will save them about $15,000 per year, so the roughly 2,000 they have already converted would be already saving the city around $150,000 per year. They have over 5,000 lights left to convert.

This page is brilliant for comparing street lighting options: http://www.grahlighting.eu/learning-centre
It’s true that high-pressure sodium lights have a slightly lower (better) watts-per-lumen rating than LEDs but they come with other drawbacks such as the light quality, colour and the higher maintenance costs due to the significantly shorter lifespan. LEDs have been rapidly improving over the last decade so this may not have been true back in 2008 and it’s likely that this information is already out of date by the time I’m typing it.

http://www.ledsvet.ru/index.php?p=index&area=1