Page:UK Traffic Signs Manual - Chapter 8 - Part 2- Traffic Safety Measures and Signs for Road Works and Temporary Situations) - Operations 2009.pdf/119

 Subject to special signs authorisation, four flashing amber lanterns complying with Section O10.9 may be fitted to the lower panel of the light arrow system for block vehicles and may be used in place of a diagram 7403 sign when the upper light arrow panel is lowered. The lanterns shall only be operated when the upper light arrow panel is lowered and is not visible to approaching drivers.

Rear-mounted flashing amber lanterns must comply with the Road Vehicles Lighting Regulations 1989 (RVLR), with a lens diameter of 300 mm ±10 mm. Each lamp must show an intermittent amber light at a rate of flashing of not less than 60 nor more than 90 flashes per minute, and in such a manner that the lights of one horizontal pair are always shown when the lights of the other horizontal pair are not shown. The optimum flash rate has been found to be 65 (±5) flashes per minute.

The light intensity of the lanterns on the principal axis should be measured when the lamps are continuously energised and shall be as follows:
 * daylight – 2000 candelas (minimum); and
 * night-time (during lighting up time) – 400 to 800 candelas.

The light intensity during hours of darkness should not exceed the maximum value of 800 candelas since this may cause glare and make the sign difficult to read. Day and night intensities should be measured with amber lenses in place and with the measuring device 7 m from the lanterns. Amber lenses should preferably be to C yellow 1 in Table 4 of BS EN 12352: 2006 or otherwise signal yellow (Class A) as specified in BS 1376.

The angle of half intensity shall be between 2.25° and 2.5°.

Adjustment of the light intensity of the lanterns for night-time operations should be carried out by an automatic light-sensitive multistage light dimming device. 117