In 1938 Fleischfarb was drafted into the Polish Army. Captured by the German Army in their invasion of Poland in September 1939, he escaped and made his way to eastern Poland, which had been incorporated into the Soviet Union. In 1943 he joined the communist-organized Polish Army, and in November 1944 he was transferred to the Ministry of Public Security, where he worked with the Soviet Komitet Gosudarstvennoi Bezopasnosti (KGB).
In postwar Poland, the Soviets coerced Jews to change their Yiddish names to Polish names, and Izak Fleischfarb became Józef Światło. During 1945–1948 he held key posts in the regional structure of the security apparatus, and in October 1948 he was transferred to the central offices to work in a unit specially created for dealing with the Polish Communist Party. Dependable and distinguished for his abilities, he was entrusted with such tasks as the arrests of Władysław Gomułka and Cardinal Stefan Wyszyński.
On 5 December 1953, while on an official trip to Berlin, Światło found his way to U.S. authorities, defected, and was transported to the United States, where the Central Intelligence Agency (CIA) used him for propaganda purposes. In September 1954 he was granted political asylum, which was trumpeted by the U.S. government. Radio Free Europe broadcast more than 100 of Światło 's programs titled Behind the Scenes of the Security and the Party, and in 1955 more than 800,000 copies of a brochure based on the broadcasts were scattered on Polish territory as part of the CIA's largest balloon campaign, Operation spotlight. Światło revelations forced Polish authorities to reorganize the security apparatus and to discharge or arrest several high-ranking Polish security officials.
Światło continued to reside in the United States under an assumed name and with CIA protection, essentially a nonperson. He died possibly in New York City in May 1985.
Kaminski, Bartlomiej. The Collapse of State Socialism: The Case of Poland. Princeton, NJ: Princeton University Press, 1991.; Michie, Allan A. Voice through the Curtain: The Radio Free Europe Story. New York: Dodd, Mead, 1963.; Schatz, Jaff. The Generation: The Rise and Fall of the Jewish Communists of Poland. Berkeley: University of California Press, 1991.