There are two traffic signal sizes, differentiated by their approximate lens diameter, 8 inch or 12 inch. The 8-inch traffic signals are approximately 30 inches tall, 9.5 inches wide and 6 inches deep. The 12-inch signals are 42 inches tall, 13.5 inches wide and 8 inches deep. These measurements apply to the main body of the signal without visors.
Incandescent and halogen bulbs in signals are increasingly being replaced with LED arrays that consume less power. In the United States, the 8-inch lights are slowly being phased out in favor of the larger and more visible 12-inch lights. There is a hybrid design that is standard in some Canadian jurisdictions, and it features one or more 12-inch lights on the same signal with one or more 8-inch lights. In the United Kingdom, 8-inch lights are the standard thanks to highly visible specialty lenses, which make a larger surface area unnecessary.
Traffic signals are generally made out of two kinds of material: cast aluminum and polycarbonate. Aluminum signals weigh about 30 pounds for the 8-inch model and 50 pounds for the 12-inch model. Polycarbonate signals are much lighter, particularly the ones using plastic lenses and aluminum reflectors. They typically weigh 15 pounds for the 8-inch signals and 30 pounds for the 12-inch signals.