After about one century since the first electrical traffic lights were invented (the first 4-way three color traffic light, by William L. Potts in 1920, and the first electric automatic traffic light, by Garrett Morgan in the same year), they can be seen now in a variety of forms, all over the world.
The traffic lights are also called traffic lamps, traffic signals, stoplights, stop-and-go lights or semaphores. They are signaling devices, which are positioned at road intersections, pedestrian crossings and other locations to control competing flows of traffic. They assign the right of passing to road users (by using an universal color code of lights – the Red-yellow-Green colors).
If initially they used as their main source of light the halogen and incandescent bulbs, now the LEDs are more and more used. This is due to their low power consumption, increasing light output and durability (they last significantly longer than bulbs).
The light pattern of a LED array can be comparable with the pattern of a halogen or incandescent bulb (using classical optics). In conventional traffic signal lighting (where standard light bulbs are used), the illumination is provided by a 67 watt, 69 watt or 115 watt medium-base light bulb.
The 3M High Visibility Signal (which is a line of products for traffic signaling) utilizes a powerful Fresnel lens and some light diffusing optics. The role of the lens is to focus the signal direction.
Here, a powerful 150W PAR46 sealed-beam lamp is used, and the light from this lamp passes through a set of two glass lenses at the rear of the signal’s optics.
One of them is called the diffuser and is made from opaque frosted glass and the other is the optical limiter lens, in which the signal’s masking is performed. In front of the signal is the 12 inch Fresnel lens, made from two acrylic layers which aligns and focuses the light.
Usually, these signals have applications where complex traffic situations exist (like: skewed intersections, left-turn pocket signals, specific multi-lane control and so on).
The traffic lights can have many types: from single, dual or three or more aspects to pedestrian and cycling crossing lights, from lights for public transport to preemption lights for emergency vehicles, from lane control to dummy lights, from racing lights to turning signal lights.
Some traffic lights can have automated cameras connected to them, which have a triggering equipment for a corresponding light, so that any vehicle which crosses can be identified.
Usually, all traffic lights have delay mechanism to allow for the residual traffic to clear. Also, they can be cascade synchronized (for example over the length of a congested main street) and can have timing displays and sound emitting devices for people with visual impairment.
In order for the bicycles to become more visible in traffic in night time or low visibility conditions and to avoid accidents, a gadget named Laser Lightlane was developed. This device is attached to the bicycle and consists in a number of lasers which are projecting on the road a red safety area. Because of the bright red lines which appear around the bicycle, cyclists are more visible and protected.
