The Traffic Signs Regulations and General Directions 2016

Beacons displayed with upright signs relating to the operation of light signals

17.—(1) For conveying the additional warning that drivers should take special care, a beacon which shows an intermittent amber light placed may be placed in combination with an upright sign provided for at item 61, 62 or 63 of the Part 2 sign table (upright signs giving information about the operation of traffic light signals).

(2) The operating requirements for a beacon mentioned in sub-paragraph (1) are—

(a) the peak intensity of light emitted by the lens or lenses of each such beacon must be—

(i) if the period between individual flashes does not exceed ¼ of a second, not less than 100 candela on the principal axis of the relevant lens;

(ii) if the period between individual flashes exceeds ¼ of a second, not less than 2000 candela on the principal axis; or

(iii) if the period between the cessation of a double flash and the start of the succeeding double flash exceeds ¼ of a second, not less than 1000 candela on the principal axis;

(b) each lens must be of such a shape and size that the perimeter of its area projected horizontally onto a vertical plane is capable of lying wholly inside a square having sides of 200 mm in length and wholly outside a square having sides of 100 mm in length;

(c) the height of the centre of the lenses from the surface of the carriageway in the immediate vicinity must be not less than 800 nor more than 1500 mm; and

(d) the rate of flashing must be not less than 55 nor more than 150 individual or double flashes per minute.