What is the validity period of a Shelf Prospectus as per the Companies Act?

Section 31.Shelf prospectus: (1) Any class or classes of companies, as the  Securities and Exchange Board may provide by regulations in this behalf, may file a shelf prospectus with the  Registrar  at the stage of the first offer of  securities  included therein which shall indicate a period not exceeding one year as the period of validity of such prospectus which shall commence from the date of opening of the first offer of securities under that prospectus, and in respect of a second or subsequent offer of such securities issued during the period of validity of that prospectus, no further  prospectus  is required.