What are the two nominal diameter sizes for vehicular signal lenses?

The standard nominal diameter sizes for vehicular signal lenses are 8 inches and 12 inches. These sizes are widely adopted in traffic signal design to ensure visibility and standardization across various jurisdictions. The 8-inch lens is typically used for various traffic signal applications, while the 12-inch lens is often used in more prominent signals that need to be visible from greater distances or in situations with higher traffic speeds. This convention helps to maintain consistency in traffic signal operations, making it easier for drivers to recognize signal meanings regardless of the location. The choices of 6 in and 10 in, 10 in and 14 in, and 12 in and 16 in do not align with standard industry practices, thus confirming that 8 in and 12 in are the correct nominal sizes.