Editing Traffic light (section)

=== Size ===
In the United States, traffic lights are currently designed with lights approximately {{convert|12|in|-1}} in diameter. Previously the standard had been {{convert|8|in|-1}}; however, those are slowly being phased out in favour of the larger and more visible 12&nbsp;inch lights. Variations used have also included a hybrid design, which had one or more 12&nbsp;inch lights along with one or more lights of {{convert|8|in|-1}} on the same light.

In the United Kingdom, 12-inch lights were implemented only with Mellor Design Signal heads designed by [[David Mellor (designer)|David Mellor]]. These were designed for symbolic optics to compensate for the light loss caused by the symbol. Following a study sponsored by the UK Highways Agency and completed by Aston University, Birmingham, UK, an enhanced optical design was introduced in the mid-1990s. 

Criticism{{by whom|date=February 2024}} of sunlight ''washout'' (cannot see the illuminated signal due to sunlight falling on it), and ''sun-phantom'' (signal appearing to be illuminated even when not due to sunlight reflecting from the parabolic mirror at low sun angles), led to the design of a signal that used lenslets to focus light from a traditional incandescent bulb through apertures in a matt black front mask. This cured both problems in an easily manufactured solution. This design proved successful and was taken into production by a number of traffic signal manufacturers through the engineering designs of Dr. Mark Aston, working firstly at the SIRA Ltd in Kent, and latterly as an independent optical designer.{{Citation needed|date=December 2008}}

The manufacturers took a licence for the generic design from the Highways Agency, with Dr. Aston engineering a unique solution for each manufacturer. Producing both bulb and LED versions of the signal aspects, these signals are still the most common type of traffic light on UK roads. With the invention of anti-phantom, highly visible Aston lenses, lights of {{convert|8|in|mm|-1}} could be designed to give the same output as plain lenses, so a larger surface area was unnecessary. Consequently, lights of {{convert|12|in|-1}} are no longer approved for use in the UK and all lights installed on new installations have to be {{convert|200|mm|0|abbr=on}} in accordance with TSRGD (Traffic Signs Regulations and General Directions). Exemptions are made for temporary or replacement signals.{{Citation needed|date=December 2008}}