Aders' book on page 43 shows a map 31 December '41 of Dunkel, Hellen, and combo zones. So it appears that there were these lighted zones in operation from Denmark to Holland. Actually on page 35 it states that in September '41 that the line became fully operational. He also states that Lichtenstein B/C was tested in the summer of '41, and the first use of AI with success was 30 Sept 1941 when Becker shot down a plane in his Do 215 B-5. So I think while the full line was not ready until Sept, various pieces were put into place well before that date.
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