Almost four decades after the orange glow first took over Chicago's night skies, the city's Transportation Department is taking steps toward converting streetlights back to a more natural -- and less light-polluting -- hue.



New ceramic metal-halide lights are replacing the 2,300 streetlamps on Lake Shore Drive, 3,000 on Western Avenue and about 11,000 lights in 300 miles of alleys throughout the city, the Transportation Department announced Friday.



The move, along with changes to 1,000 stop lights, is expected to save about $1.8 million a year.



The city is using a $13.8 million grant from the U.S. Department of Energy to replace the orange streetlights, which were first installed in the mid-1970s in an earlier bid to increase energy efficiency.



The new lights use less electricity than the old sodium vapor lights, reducing costs by between about $40 and $70 per light, with a lifespan of two to three years longer than the typical sodium vapor light, which lasts about 5 years, according to a release from the Transportation Department.



The new lights have a more full light spectrum than sodium vapor, so they appear just as bright or brighter than the orange lights and show the true colors of things much better. At the same time, they reduce the amount of sky glow by up to 100 percent, depending on the fixture used, which will make Chicago's orange city glow a thing of the past once all street lamps are replaced.



At the same time, the city is replacing older stoplights at 1,000 intersections with new LED stoplights.



The new streetlights are now the city's standard light, replacing sodium vapor lamps that Mayor Richard J. Daley first had installed in the mid-1970s to increase the level of street lighting and decrease costs.



Conversion to sodium vapor lights on Chicago's residential streets started in 1974, at a cost of $10 million, and followed up with another $10 million program that converted streetlights on major thoroughfares to sodium vapor lights. In all, the city converted almost 173,000 lights to sodium vapor between 1974 and about 1977.



But while they drew some praise for driving the shadows from city streets, the orange lights always have had their critics. Tribune architecture critic Paul Gapp called the lights "a city-wide orange abomination," and the local chapter of the American Institute of Architects and others crusaded against them, to no avail.



Since the large-scale adoption of sodium vapor lights in the United States and elsewhere, studies have been done showing that they can hamper police identification of suspects because they decrease people's ability to tell one color from another, because they make everything look orange at night.



The city estimated in 1973 that converting to sodium vapor lights throughout the city would save about $125,000 a year in electricity and maintenance costs -- or about $635,000 in today's dollars -- by converting about half its 182,500 lights to sodium vapor. Adjusted for inflation, that's almost exactly how much the city hopes to save by converting just 16,000 lights this year.



The change also is estimated to decrease carbon dioxide emissions by about 15,000 metric tons a year, according to the Transportation Department.



chicagobreaking@tribune.com