3. Any dimension of a sign erected in accordance with the provisions of this Instrument which varies from the dimension specified in the diagram set out in the Schedule to these Regulations relating to a sign of that size shall be treated as being the dimension specified in the diagram if the variation does not exceed 2½ per cent of that dimension.
4.—(1) Every terminal sign of size 1 or 2 shown in a numbered diagram, when erected on a trunk or principal road within 50 metres of a street lamp lit by electricity—
(a) shall throughout the hours of darkness be continuously illuminated by means of internal or external lighting, and may also be illuminated by the use of reflecting material, or
(b) shall throughout the hours of darkness while the street lamp is lit be continuously illuminated by means of external lighting, and shall also be illuminated by the use of reflecting material.
(2) If any sign is required by the foregoing paragraph of this Regulation to be continuously illuminated by lighting throughout the hours of darkness, or throughout such hours while a street lamp is lit, every sign shown in the same diagram as the first-mentioned sign which is erected at or near the same point on the road or the same junction for the same purpose as the first-mentioned sign shall be continuously illuminated throughout the same period by the same means of internal or external lighting as the first-mentioned sign, and, if any of the said signs is illuminated by the use of reflecting material, every other such sign shall be similarly illuminated.
(3) Any sign shown in a numbered diagram which is not required by the foregoing paragraphs of this Regulation to be illuminated by lighting throughout the hours of darkness, or throughout such hours while a street lamp is lit, may be illuminated throughout the hours of darkness by means of external or internal lighting, or throughout any period during the hours of darkness by means of external lighting and the use of reflecting material and if so illuminated paragraph (2) of this Regulation shall apply as if it were a sign required by paragraph (1) of this Regulation to be illuminated by lighting throughout the hours of darkness, or throughout such hours while a street lamp is lit.
(4) Every sign shown in a numbered diagram which is not illuminated throughout the hours of darkness by lighting shall be illuminated by the use of reflecting material.
(5) Where any sign shown in a numbered diagram is illuminated by a means of external lighting, that means shall be either fitted to the sign or to the structure on which it is mounted or otherwise specially provided.
(6) Where reflecting material is used on any sign shown in a numbered diagram it shall be the same colour as, and extend throughout, that part of the sign to which it is applied, except that no reflecting material shall be applied to any part of a sign coloured black.
(7) In this Regulation_
"principal road" means a road for the time being classified as a principal
road—
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