In 1930, he became a broadcaster with the CBS Radio network, delivering a nightly news and commentary program. After two years, he switched to the NBC Radio network but returned to CBS in 1947. In contrast to today's practices, Thomas was not an employee of either NBC News or CBS News. Prior to 1947, he was employed by the broadcast's sponsor Sunoco. He returned to CBS to take advantage of lower capital-gains tax rates, establishing an independent company to produce the broadcast which he sold to CBS. He hosted the first-ever television news broadcast in 1939 and the first regularly scheduled television news broadcast (even though it was just a camera simulcast of his radio broadcast) beginning on February 21, 1940 over local station W2XBS (now WNBC) New York. It is not known whether all or some of the radio/TV simulcasts were carried by the two other television stations capable of being fed programs by W2XBS at the time, which were W2XB (now WRGB) Schenectady and W3XE (now KYW-TV) Philadelphia).  In the summer of 1940, Thomas anchored the first live telecast of a political convention, the 1940 Republican National Convention which was fed from Philadelphia to W2XBS and on to W2XB. Reportedly, Thomas wasn't even in Philadelphia, instead anchoring the broadcast from a New York studio and merely identifying speakers who addressed the convention.  The television news simulcast was a short-lived venture for him, and he favored radio. Indeed, it was over radio that he presented and commented upon the news for four decades until his retirement in 1976, the longest radio career of anyone in his day (a record later surpassed by Paul Harvey). "No other journalist or world figure, with the possible exception of Winston Churchill, has remained in the public spotlight for so long," wrote Norman R. Bowen in Lowell Thomas: The Stranger Everyone Knows (1968). His signature sign-on was "Good evening, everybody" and his sign-off "So long, until tomorrow," phrases that he would use in titling his two volumes of memoirs.

Answer this question "how long did this last" by extracting the answer from the text above.
1947.