(5) The sign shown in diagrams 503, 604 and 814, shall be illuminated throughout the hours of darkness by a means or internal or external lighting.
(6) The sign shown in diagram 828.1 shall be illuminated by an intermittent unit flashing at a rate of not less than 54 not more than 90 flashes per minute during such times only as it is necessary that the sign shall be illuminated for the purpose of indicating the information shown in diagram 828.1.
(7) Where at sign to which any of the foregoing paragraphs applies is placed on or near a read for the purpose of conveying a warning or information from time to time to vehicular traffic, or in connection with a statutory prohibition, restriction or requirement which relates to such traffic but does not apply at all times, that sign shall be illuminated in accordance with such of the foregoing provisions of this Regulation its apply to it but only during such times as, for the said purpose or in the said connection, it is necessary that the sign shall be visible from a reasonable distance to drivers of approaching motor vehicles, any other provision of this Regulation to the contrary notwithstanding.
(8) Subject to the foregoing paragraphs of this Regulation and in Regulation 19, any sign shown in a diagram in Schedule 1 may be illuminated by a means of internal or external lighting and where, subject as aforesaid, the means in lighting any such sign is external, then that means of lighting shall be either fitted to the sign or to the structure on which it is mounted or otherwise specially provided.
16. Where a sign shown in a diagram in Schedule l that being a sign consisting of a plate) is illuminated by a means of fighting in accordance with the revisions of Regulation 15 and a plate shown in a diagram in that schedule is used in conjunction with that sign, the said plate shall, unless the means of lighting provided for the illumination of the sign adequately illuminates the plate, be illuminated, during such times as the sign is illuminated, by a means or lighting and that means of lighting shall accord with that one of the methods of lighting, namely, internal or external adopted for the illumination of the sign.
17.—(1) The signs shown in diagrams 560 and 561 shall not be illuminated by the fitting of a means or internal or external lighting.
(2)(a) If the sign shown in diagram 560 has a diameter of 150 millimetres, that sign shall be illuminated by either of the methods prescribed at (i) and (ii) of sub paragraph (c) below and not otherwise
(b) If the said sign has a diameter of 75 millimetres or more but less than 150 millimetres, that sign shall be illuminated by either of the methods prescribed at (iii) and (iv) of sub-paragraph (c) below and not otherwise.
(c) The methods referred to in sub-paragraphs (a) and (b) above are:—
(i)by the use of 14 circular reflectors of the corner type, each reflector having a diameter of 22 millimetres,
(ii)by the use or reflecting material extending over the whole surface of the sign,
(iii)by the use of a single circular reflector of the corner cube type extending over the whole surface of the sign,
(iv)by the use of reflectors consisting of bi-convex lenses extending over the whole surface of the sign.
