Editing Traffic light (section)

=== Programmable visibility signals ===
{{Multiple image
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| image1            = First and Mill 3Ms img14.jpg{{!}}3M traffic signals in Shelton, Washington, as seen off-axis from the intended viewing area. These signals appear to be "off" or invisible to adjacent lanes of traffic during the daytime. Only a faint glow can be seen when viewed at night.
| image2            = First and Mill 3Ms img07.jpg{{!}}3M traffic signals in Shelton, Washington, as seen from the signal's intended viewing area. Special light-diffusing optics and a coloured Fresnel lens create the indication
| footer            = Traffic signals installed in [[Shelton, Washington]], seen off-axis from the intended viewing area (''top'') and from the signal's intended viewing area (''bottom'').{{pb}}From off-axis, these signals appear to be "off" or invisible to adjacent lanes of traffic during the daytime. Only a faint glow can be seen when viewed at night.
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Signals such as the 3M High Visibility Signal utilize light-diffusing optics and a [[Fresnel lens]] to create the signal indication. The light from a 150 W PAR46 sealed-beam lamp in these "programmable visibility" signals passes through a set of two glass lenses at the back of the signal. The first lens, a frosted glass diffusing lens, diffuses the light into a uniform ball of light around five inches in diameter. The light then passes through a nearly identical lens known as an optical limiter (3M's definition of the lens itself), also known as a "programming lens", also five inches in diameter.{{Citation needed|date=July 2020}}

Using a special aluminium foil-based adhesive tape, these signals are "masked" or programmed by the programming lens so that only certain lanes of traffic will view the indication. At the front of these programmable visibility signals is a 12" Fresnel lens, each lens tinted to meet United States [[Institute of Transportation Engineers]] (ITE) chromaticity and luminance standards. The Fresnel lens collimates the light output created by the lamp and creates a uniform display of light for the lane in which it is intended.

In addition to being positioned and mounted for desired visibility for their respective traffic, some traffic lights are also aimed, louvered, or shaded to minimize misinterpretation from other lanes. For example, a Fresnel lens on an adjacent through-lane signal may be aimed to prevent left-turning traffic from anticipating its own green arrow. Intelight Inc. manufactures a programmable traffic signal that uses a software-controlled LED array and electronics to steer the light beam toward the desired approach.<ref>{{cite web|url=http://intelight-its.com/product/esb-signals/item/34-intelight-esb-traffic-signal-head.html|title=Intelight ESB Traffic Signal Head|work=intelight-its.com|access-date=21 June 2013|archive-url=https://web.archive.org/web/20140808220251/http://intelight-its.com/product/esb-signals/item/34-intelight-esb-traffic-signal-head.html|archive-date=8 August 2014|url-status=dead}}</ref> 

The signal is programmed unlike the 3M and McCain models. It requires a connection to a laptop or smartphone with the manufacturer's software installed. Connections can be made directly with a direct-serial interface kit, or wirelessly with a radio kit over WIFI to the signal. In addition to aiming, Fresnel lenses, and louvers, visors and back panels are also useful in areas where sunlight would diminish the contrast and visibility of a signal face. Typical applications for these signals were skewed intersections, specific multi-lane control, left-turn pocket signals, or other areas where complex traffic situations existed.

[[File:Colors of a Stoplight- Animated- Lewiston.gif|thumb|right|An animated GIF shows a traffic light in 3 reverted phases: red, yellow, then green]]