ढक देना  =  cover
To cover sth written or printed with black ink, etc so that it cannot be read

बेहोश होना  =  lose consciousness
The plane dived suddenly,causing the pilot to black out.

में अंधकार कर देना  =  put out lights
Houses blacked out during an air raid.

बेहोश हो जाना
He blacked out when somebody hit him on the head.