The lights will go dark at 23d and Market Streets in Philadelphia shortly after the start of the new year.
Peco Energy Co., whose headquarters has displayed community and other messages - about 17,825 of them, a company spokeswoman said - since July 4, 1976, will be installing a new sign.
The new one will feature energy-efficient LED lighting with color and graphic capability. The replacement system is expected to be unveiled in mid-summer 2009, the company said.
As for those several months without the sign: "We're going to miss it, too," Peco spokeswoman Cathy Engel said. ". . . It's such a part of the fabric of Philadelphia that those of us at Peco take pride in."
Unfortunately, she said, "We couldn't figure out a way to upgrade the system without taking down the old one."
The current electronic board, which has flashed messages about community and nonprofit groups, as well as about Peco, consists of 2,600 bulbs. It's 38 feet high and 148 feet long along the north and South sides of the building, and 71 feet long along the east and West sides, Peco said.
The new system will use the latest in LED lighting technology, and is expected to use 20 percent less energy and provide several thousand dollars of additional savings in bulb-replacement costs.
The system is being installed by C. Erickson and Sons of Philadelphia in conjunction with Salt Lake City-based Yesco.
Replacement of the sign is part of Peco's "green" initiative, which includes installation of a "green" roof at the company's headquarters building.