One of Dallas' oldest law firms is moving into new digs this week. Thompson & Knight is filling up six floors totaling 180,000 square feet in One Arts Plaza in the Dallas Arts District. The offices offer impressive and innovative features like a biometrics security system and a number of environmentally conscious design elements that helped the it secure registration with the U.S. Green Building Council. Lead-free glass allows better transmission of light inside the offices and a specially designed "Mother's Room" has lactation equipment and other amenities for working mothers. The firm is pursuing LEED-CI Silver Certification, which recognizes interiors that are healthy, productive places to work and that are less costly to operate and have a reduced environmental footprint. The firm's lease fills out the space at the recently completed One Arts Plaza in the heart of the city's Arts District.