As far as I read manual pages, scanf says that 'l' length modifier indicates (in case of floating points) that the argument is of type double rather than of type float, so you can have 'lf, le, lg'.
As for printing, officially, the manual says that 'l' applies only to integer types. So it might be not supported on some systems or by some standards. For instance, I get the following error message when compiling with gcc -Wall -Wextra -pedantic
a.c:6:1: warning: ISO C90 does not support the ‘%lf’ gnu_printf format [-Wformat=]
So you may want to doublecheck if your standard supports the syntax.
To conclude, I would say that you read with '%lf' and you print with '%f'.