Saving Energy with Networked Streetlights

Saving Energy with Networked Streetlights

How an electrical power system can become part of an outdoor local area network

As budget-conscious municipalities around the country continue to look for ways to save money any way they can, a concept called “adaptive lighting” is gaining attention. Currently being tested and implemented in many cities, this lighting approach allows roadway lighting levels to change in response to time of night, traffic conditions, or security needs. An example of the communications industry’s goal to achieve system convergence by using networks and a common infrastructure, this new technology could be considered a component of intelligent transportation systems, which include closed circuit television (CCTV) systems, radio frequency identification (RFID) systems, and traffic control and speed monitoring systems — to name just a few.

Deeming communications/control systems as integral elements to achieving energy and operational efficiency, the lighting industry is tuned to smart networking, several examples of which have been demonstrated at past Lightfair International trade shows. At last year’s show, for example, there were several interior office light control systems on display that used Cat. 5e unshielded twisted-pair (UTP) cabling to create a local area network (LAN) and interconnect various system components. Additionally, one of the educational sessions was titled, “The Integration of Lighting and IT.” By adding a communications capability, the conventional street lamp is being updated to join this “green” revolution, a trend that will inevitably be reiterated at this year’s Lightfair event to be held in mid-May in Philadelphia.

Currently, street and highway illumination consumes about 2% of the nation’s electricity, according to the U.S. Department of Energy (DOE). For more information on what variety of lamp is most frequently used where, see Lamp Type Review. Photocell controls turn street and roadway lighting on at nightfall and off at daybreak. As a result, the same level of illumination is provided at 7 p.m. (peak traffic) as at 2 a.m. (non-peak traffic). By having a method of switching (or dimming) the light level based on activity, a municipality can cut down on “light spillage” — the term used by city planners for lighting that’s not needed. Several lighting equipment manufacturers offer a network-based automated asset management system for roadway and street lighting luminaires that are accessed by a two-way communications system.

How it works

Roadway luminaires typically feature a receptacle on the top side of the enclosure. The receptacle allows the installer to plug in a photo detector device, which automatically turns on the lights at dusk and off at dawn. With new networking technology, a module that looks similar to a photo detector mates with the receptacle and still does the light sensing; however, it also serves as a network node that can switch power on and off (see Photo). In addition, users can connect it to a monitoring circuit that can keep track of many of the performance aspects of the light source and the electric power system. Each module serves as a node in a wireless network. Therefore, information on the status of the light source, such as an outage or malfunction, is sent via a wireless RF system to a local access point (AP). The AP aggregates information from hundreds of nodes and then communicates that data — either by wireless or wired network — back to a secure server at a network operations center (NOC).

A wireless mesh network is the preferred deployment for this system, because each luminaire node can retransfer data it receives at 250 kbits/sec. Generally, the IEEE 802.15.4 specification is the basis for the physical and media access control layers of the network.

The global positioning satellite (GPS) location of a light pole, which is captured when a node is installed, allows a problem fixture to be identified immediately (see Resolution Speed), allowing an operator at the NOC to send a crew to the exact pole with all of the needed repair components. The
operator can also obtain related electrical system information, such as ground fault detection and revenue-grade power metering, as well as automatically create a work order. Once street lighting is networked, the old method of performing maintenance — where the electric utility relies on call-ins from the public to report a streetlight outage, causing technicians to drive around to locate the non-operating luminaire — is eliminated.

System development time line

In development for more than 15 years, electric lighting management systems (ELMSs) initially offered only a limited number of capabilities, so the installations focused simply on energy management — that is, whether or not the light fixture was powered and whether a schedule could be remotely applied to each fixture. Later, basic power metering functions were added to confirm operation and assist in the diagnosis of fault conditions.

Originally, the systems were proprietary, requiring a dedicated personal computer (PC). They often were tied to a lengthy and expensive maintenance contract with the vendor. Moreover, many of the systems required a user to host its data on the vendor’s Web server at a sizable monthly subscription fee. Proprietary protocols eliminated any opportunity for competitive bidding and economical system expansion.

To overcome these deficiencies, the National Electrical Manufacturers Association (NEMA) initiated the development of the National Transportation Communications for Intelligent Transportation System Protocol (ITS) in 1992. NEMA, along with American Association of State Highway and Transportation Officials (AASHTO) and the Institute of Transportation Engineers (ITE), formed a joint standardization project that resulted in the ITS NTCIP 1213 “Electric Lighting and Management Systems” standard, which incorporates existing national and international networking standards that cover data (or object) definitions and communications protocols. (Note: Object definitions refer to particular types of roadside devices and control products, such as traffic signal controllers or dynamic message signs.)

Benefits of networked lighting systems

Roadway lighting levels can be infinitely adjusted to suit weather/atmospheric conditions, such as lowering the light level on a rain slick highway or during fog to give drives improved visibility. In an urban area, a crosswalk can have a higher light level than a mid-block area. In the event of a traffic accident, emergency personnel could bring the dimmed light up to full, just in the area of the accident. In other cases, police, fire rescue, or medical personnel could reach their destination faster if the pole-mounted LED fixture in front of a home or business was flashing continuously as a beacon.

Because the electrical circuits serving outdoor lighting systems are installed below sidewalks and in other areas that have public access — and are subject to water, moisture infiltration, and accident damage — the monitoring of ground fault current can alert maintenance personnel before a person is injured from an electric shock.

Real-world examples

Currently, many cities are undertaking field trials, or pilot projects, to evaluate automated asset management systems as related to their lighting systems.

One good case in point is the city of Los Angeles’ Bureau of Street Lighting, which maintains the second-largest municipal street lighting system in the country (240,000 streetlights). The Bureau is using an asset management system with a wireless communication connection, operating on the 2.4-GHz unlicensed broadcast band. An operator at the control center accesses the data on a password-protected website via an Internet connection. The information at the utility’s NOC includes total lamp burn time, total ignitions, last measured voltage, and current and power factor. It also enables fault reporting at the desktop regarding the following conditions: cycling lamp, photocell oscillating or not working, line voltage fault, or inoperative monitoring device.

In 2007, the City of New Orleans launched a pilot program to monitor and control its street lighting system. In this case, the asset management system vendor provides status report four times a day — or on-demand — to city oversight administrators. The status report, created at the monitoring center, notifies repair crews and offers a preliminary diagnosis. The collected data will permit any repair contractor in the future to better understand the city’s street lighting service needs, allowing contractor bids to be more accurate. The city can then award contracts that reflect actual risk conditions, thereby reducing its operating costs.

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