Traffic Light design
In the United States, traffic lights are currently designed with lights approximately 12 inches (300 mm) in diameter. Previously the standard had been 8 inches (200 mm), however those are slowly being phased out in favor of the larger and more visible 12 inch lights. Variations used have also included a hybrid design, which had one or more 12 inch lights along with one or more lights of 8 inches (200 mm) on the same light. For example, these “12-8-8″ (along with 8-8-8) lights are standard in most jurisdictions in Ontario, Manitoba, and British Columbia (that, is, the red light is 12 and others 8, making the red more prominent).
In the United Kingdom, 12 inch lights were implemented only with Mellor Design Signal heads designed by David Mellor. These were designed for symbolic optics to compensate for the light loss caused by the symbol. With the invention of anti-phantom, highly visible SIRA lenses, lights of 8 inches (200 mm) could be designed to give the same output as plain lenses, so a larger surface area was unnecessary. Consequently lights of 12 inches (300 mm) are no longer approved for use in the UK and all lights installed on new installations have to be 200 millimetres (8 in) in accordance with TSRGD (Traffic Signs Regulations and General Directions). Exemptions are made for temporary or replacement signals.
In the state of Victoria, Australia, lights used to have long visors with a slanted cut on the side nearest the road (for approach side) and none for the opposite side. These lights also had a sort of horizontal filter covering the upper half of the visor, except on arrows. This design eliminated or minimised washout of the light by a low-lying sun. This type of design has yet to surface outside of Victoria. LED-based lights, however, do not follow this standard, adopting the national standard of having a short visor and cut on both sides, although the cut is also applied to the lights on the opposite side of the junction. Some installations do not have cuts on the opposite side. There exists at least 1 LED-based light using the visor and filter set of its predecessor.