Transportation crews are installing new energy-efficient light bulbs along Maine’s interstate highways. Department of Transportation crews are replacing 350 light bulbs in 105 light towers in the coming weeks in Kittery, Saco, Portland, Falmouth, Waterville and Bangor, as well as at the Medway rest areas. The new LED bulbs will save the department $135,000 a year in electric costs. It now costs about $200 a month to power three bulbs in a light tower, but that will drop to $65 a month with the new bulbs. The savings also will allow the lights to stay on all night, rather than being turned off at 11 p.m. as they now are. Each 290-watt bulb weighs 55 pounds.