If you're wondering when Ameren Illinois will replace the purplish mercury vapor lights and orange sodium lights in your neighborhood, don't worry. The crews will get around to it. 

For the most part, they're installing energy-efficient LED lamps gradually--one by one as the old lights burn out. Spokesman Brian Bretsch says sometimes, the utility company does an entire street or highway in one shot.

Some cities own at least some of their street lights. It's up to them to decide what to replace them with and when, but they're usually going with LED's these days.