2close,
Over here, when a pilot qualifies as an instructor, his instructor ratings include several restrictions, for example "No applied instrument instruction", and "No aerobatic instruction". One such restriction is "No night instruction".
In order to remove the night instruction restriction, an instructor has to complete a recognised course, which includes some ground school (I think it's 5 hours), and one of hour night flying. Then, of course, you have to pay the CAA a small fee to get them to amend your license.
FFF
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