At this time, SPOT Devices is no longer offering an In Road Way Light (IRWL) product family. However, there remain many installations utilizing these roadway lights. The last version of these lights is discussed here. The last version of the solar powered wireless controlled version is the V2 version and the hardwired version is the V3 version. The wireless version predates the wired version by approximately four years. This failure report discusses observed modes of failure of these lights. This is followed by a brief introduction of a Silicon Constellations product, the LumiNova. The LumiNova can be retrofit to these crosswalks either version of the SPOT Devices IRWL without any additional street work or modifications. This cost reduction can be important to installations which must be maintained.
The V2 and V3 SPOT Devices IRWL are constructed very differently.
The V3 wired IRWL is made of steel and uses refraction in an attempt to direct the light beam somewhat horizontal through almost flat plastic windows.
The V2 wireless version is quite different. It is larger, reflecting the need for a larger surface area for the solar panels, and the light transmission method is based on reflecting the light from two LEDs mounted lower in the housing out through a periscope type window. The housing appears to be an aluminum casting.
It is estimated that this wireless version preceded the wired version on the development path by approximately four years.
The following photograph illustrates an incident of destruction of the elevated plastic periscope on a wireless SPOT Devices V2 IRWL. The protective steel arch is gone and the plastic casting has been shattered.
This type of destruction of this device is not surprising. Any part of an IRWL that is above the road surface is subject to endless mechanical stress and tremendous mechanical shock from street sweepers, among other things. The steel arch used to protect the plastic periscope rises sharply from the surface of the light with little taper. This does not allow any distance for a striking object to "ride up" and glide over the top of the light.
Notice that the arch is attached with two screws. These two screws attach the arch to the cast iron underlying base fixture that holds the light to the road. The failure of this arch can be traced to shearing of the screws, probably due to a heavy strike. Once the screws have sheared, the arch is gone. The remaining stud of the screw on the right hand side of the light can be seen in Figure 3. The underlying plastic periscope does not survive, as illustrated in Figure 3.
The mechanical stress on the SPOT Devices V2 wireless IRWL produces a second type of failure. The continued pounding in the real world causes cracking of the plastic window. Therefore, even if the steel arch remains intact, the cracks allow for water to enter the light which eventually leads to corrosion of the circuitry.
The cracking of this plastic casting clearly leads to moisture intrusion in the case as the following photo shows. Even on a sunny day the moisture is visible beneath the protective steel arch.
Failure of this light is due to at least two stresses.
The SPOT Devices V3 wired IRWL is constructed quite differently than the predecessor V2 wireless version. Compare Figures 1 and 2. The low profile design means the periscope annihilation problem is not a failure mode, however, the nature of the construction of the light leads to moisture intrusion followed by circuitry corrosion which ultimately leads to failure of the light.
It is pointed out that the low profile design has a non destructive failure mode. There are considerable problems that occur in attempting to use Brewster angle refraction to direct light. The clouded and damaged surface leads to beam diffusion and internal reflection. This leads to dimming and eventual extinction of the light.
There are two moisture issues with the SPOT Devices V3 wired IRWL. The first is the connector used between the light and the connecting wiring used to power and control the light. This connector is illustrated here in Figure 7.
This connector mates with the male version of the connector which is situated at the bottom of the mounting fixture. This forms the interconnection between the light and the wiring of the system. The astonishing feature of this interconnection is that it is done blind with no mechanical clamp or seal to guarantee the integrity of the interconnect. In fact, it is not possible to even verify that the two rubber surfaces on the top of each connector are even in contact with each other. Nor, is it possible to verify that excess contact pressure does not distort the connector and lead to further water intrusion.
The second source of moisture and water intrusion into the SPOT Devices V3 wired IRWL comes from the potting used internal to the light. Essentially, the light is flooded with a plastic or silicon potting material. Curiously, the silicon formulation chosen sets up very hard. This hard set up has a very significant problem. Once cured, or hardened, the material shrinks slightly and separates from the circuits it has been assigned to protect. Water and moisture seeps along these channels until it encounters metal wiring which results in the inevitable corrosion.
The hard potting method is shown here in Figure 8. Much of the potting has been removed, however, strips of the material are shown in black near the perimeter of the interior.
Finally, the negative effects of this method of manufacturing are shown in the corrosion on the LED board used in the light. This is shown in Figure 9.
Finally, it appears the bathtub design of the cast iron base fixture only exacerbates the corrosion problems of the interconnect between the light and the external wiring. A picture of a corroded base fixture is illustrated in Figure 10. Note the connector to the external wiring located at the lowest point of the bathtub fixture.
Water seeping around the light pools at the bottom of the fixture and can only be removed by the slow process of evaporation. There is no really effective way to drain this water. Finally, a picture of both the base fixture and the V3 wired light is included to illustrate the overall corrosion problem with this light.
There are many established SPOT Devices crosswalks, both of the wired and wireless variety. Unfortunately, replacement parts are no longer available for maintenance of these crosswalks. In addition, the installed base fixtures embedded in the streets represents a sizable investment in money and municipal effort.
In an effort to support municipalities and other users of the SPOT Devices systems, Silicon Constellations has developed a product that can be retrofit to the established SPOT Devices base fixtures. This includes both the V2 wireless version and the V3 wired version. This is the LumiNova product line.