Changing the width of ledger lines

If you want to modify the width of ledger lines (for example to make them wider) you can do this by overriding the values of LedgerLineSpanner.length-fraction and (optionally) LedgerLineSpanner.minimum-length-fraction.

\version "2.24"

% Override LedgerLineSpanner.length-fraction to change the width
% of ledger lines. Its default setting is 0.25 which extends ledger
% lines beyond the note head on each side by 0.25 times the width
% of the note head. (1.0 is equal to the width of the note head.)
%
% LilyPond will automatically shorten ledger lines to avoid collisions.
% LedgerLineSpanner.minimum-length-fraction sets their minimum 
% length (i.e. smallest possible length) for such cases of potential 
% collision. It guarantees that ledger lines will always be at least 
% that wide. Its default setting is 0.25  (It should always be less 
% than or equal to the value of LedgerLineSpanner.length-fraction.)
%
% See the illustrations here:
% http://lilypond.1069038.n5.nabble.com/Widening-ledger-lines-by-overriding-LedgerLineSpanner-td162842.html#a162850

notes = {
  d4 e f g 
  c''' d''' e''' f'''
}

<<
\new Staff \with {
  instrumentName = "default "
} {
  \notes
}
\new Staff \with {
  instrumentName = "wider "
  \override LedgerLineSpanner.length-fraction = #0.45
  \override LedgerLineSpanner.minimum-length-fraction = #0.45
} {
  \notes
}
>>