Whether for Smart Cities or not, don’t miss any details when designing LED lighting systems and associated sensor hubs.
“Smart City” refers to the integration of communications and physical assets into a cohesive network to facilitate a safer, more livable, and more energy-efficient environment for the people who live there.
In a Smart City, real-time information is provided to administrators from a city-wide deployment of sensors and monitors. Depending on the design, the collected data can enable any number of capabilities, such as monitoring weather and air quality, adjusting traffic signals to relieve congestion, adjusting mass-transit schedules to meet changing demand, and more rapid deployment of emergency responders.
Kansas City has realized one of the more well-known examples of the Smart City concept in a two-mile corridor. The implementation uses sensors integrated into outdoor street lighting to generate a real-time picture of traffic patterns, street car transit, and even open parking spaces.
While the Smart City installations throughout the Unites States – and the rest of the world – vary, one common denominator is the use of outdoor LED street lighting as the “anchor” for integration of the various sensors needed to collect data. This means that in addition to suitable lensing and housing designs that direct the output light to where it’s needed while minimizing glare and skyglow, an optimal outdoor LED lighting design needs to include additional performance features for Smart City realization. Here are some of things to think about:
Energy Monitoring and Metering – because city administrators need data in order to evaluate the overall performance of the outdoor lighting system and identify ways to make the system more efficient, lighting should include capabilities for data collection and transfer. Relevant data includes ambient light levels, on-time, energy consumption, and status (e.g., full on, dimming level), transferred at pre-determined intervals to the network hub for collection and analysis.
Dimming and Color Tuning – to fully realize the energy savings potential of integrating outdoor street lighting into a Smart City network, luminaires should be dimmable both via scheduling and in response to changing environmental conditions. For example, to minimize energy usage, lights might follow a pre-programmed schedule (Figure 1).
Figure 1 Example dimming schedule for LED street lighting
In emergency situations, administrators should have the capability to both override the schedule, and also to transition the light from a warmer white (which has a lower impact on skyglow and is generally preferred in residential areas) to a cooler white, which provides greater visual acuity for emergency responders.
Figure 2 Example of cooler white street lighting to provide greater visual acuity in emergencies (source: US Dept. of Energy)
Over-voltage protection – the over-voltage risk for outdoor products resulting from lightning and switching pulses as well as electrostatic discharge is significantly higher than for products meant for use indoors. Mitigation can be achieved through the inclusion of overvoltage protection both external to the electronics and as part of the driver design.
Reliability – temperature and temperature fluctuation, humidity, dust and water ingress, UV exposure, and vibration are all causes of outdoor luminaire performance degradation or failure. While the LED packages used in the luminaire are most sensitive to high temperatures, system components like drivers, optics, and the integrated sensors, may be affected by other environmental factors. A comprehensive reliability and QA program, including robustness testing, can help mitigate these risks.
Maintainability and upgradability – GPS location, luminaire status, sensor status, input voltage and current, and internal temperature are the types of information that a Smart City outdoor lighting product can provide to facilitate repairs or component upgrades with minimal downtime. Design for maintainability/upgradability in terms of providing easy access for parts replacement or cleaning is important to overall lighting system viability.
Interoperability – the ANSI C137 Lighting Systems Committee defines interoperability as “the ability of systems or systems components to transmit, receive, interpret, and/or react to data and/or power and function in a defined manner”. Even though the terms are not equivalent, interoperability is often confused with the term “compatibility.” Compatibility refers to whether a device adheres to a particular standard. Devices compatible with the same standards should be interoperable for the functionality defined under that standard. Confirming interoperability of the lighting system components, e.g., the luminaire, sensors, and network hardware and software, reduces the risk associated with hardware and software obsolescence.
Security – last, but definitely not least is the consideration of network security. This aspect of Smart City design seems to be the least defined in terms of roles and responsibilities of suppliers vs. buyers, and therefore, most worrisome. While not a luminaire design consideration per se, it’s important to keep in mind that any device on a network could be susceptible to hacking.
Smart City implementations will undoubtedly grow as part of the on-going conversion to LED technology for outdoor street lighting. Look for a Smart City network coming to a town near you, and if you’re involved in design or operations, tell us about it below.
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—Yoelit Hiebert has worked in the field of LED lighting for the past 10 years and has experience in both the manufacturing and end-user sides of the industry.