Even if you didn’t watch “The Guiding Light,” you probably know someone who did. The CBS soap opera is the longest-running drama in TV and radio history, and it comes to an end after 72 years and more than 15,700 episodes on Friday. Remarkable. The continuing story — the title refers to a lamp in the study of a minister who was a major character — debuted on NBC radio in 1937 as a 15-minute serial. It came to CBS television on June 30, 1952. The demise of TGL continues the shrinking of the daytime soap in the changing television landscape. Once there were a dozen daytime dramas. Now there will be seven. “The Guiding Light” will be replaced by a new version of “Let’s Make a Deal.” Several well-known actors appeared on TGL — Kevin Bacon, JoBeth Williams, James Earl Jones, Allison Janney, Hayden Panettiere, Melina Kanakaredes, Paul Wesley and Brittany Snow.