What is a smart street lighting system?
Simply put, a smart street lighting system incorporates clusters of streetlight lamps that can communicate with each other and provide lighting data to a local concentrator. The concentrator manages and transmits the relevant data, often via a digital cell phone modem, to a secure server that captures the data and presents it in a web-browser interface.
But an extra layer of value is added: two-way communication. A smart street lighting system allows facility managers to remotely control street lights while keeping track of electrical power consumption in the lamps and in the driving circuits.
Compared to traditional autonomous street lights, monitored street light networks help reduce maintenance costs - the lamp status is monitored, and scheduling maintenance becomes more efficient and cost-effective. In case a lamp or string of lamps fails, there is no need for roving inspection; the problematic lamp can be pin-pointed remotely.
Also, if the night is brightly moon lit, for example, smart street lighting also assures reduced energy use by dimming or brightening the lights by remote. This can be done according to weather conditions, like fog or rain, or to a preset schedule. An efficient collection of data is guaranteed as well, which city planners can use to expand light systems as their cities grow.
Obviously, cities are the primary consumers of smart street lighting because of the savings of energy and maintenance monies as well as the ability to re-allocate public funds towards other programs – a win-win situation for the community.
Smart as a post
The basic component of a smart street lighting system is the intelligent lamppost, which integrates these three blocks:
1. Advanced power stages (lamp ballast or driver) aimed to drive the lamps with the highest efficiency
2. Communication interfaces to allow the assembly of a digitally monitored, secure, and reliable network
3. An optional addition of various smart sensors to monitor weather conditions, lamppost inclination, and air pollution
Intelligent street lighting does more than simply shine on the road. It has to assure specific values of luminance, illuminance or dimness, uniformity, and glare according to the road type in order to guarantee maximum visual safety to drivers and pedestrians. For this purpose, highly performing luminous sources, such as High Intensity Discharge (HID) lamps and LEDs lamps, are used.
The intelligent lamppost begins with its ballast or driver. Innovative solutions for HID electronics ballast have been produced that guarantee increased lamp life, enhanced lumen maintenance, and decreased energy consumption. These solutions can range from electronic ballasts for driving high power lamps (150W & 250W), to state-of-art-solutions for low and medium power applications (70W & 35W). For powering LED street lights, engineers require a large portfolio of solutions that address both electrically isolated and non-isolated applications, driving single or multiple LED strings for different levels of output power (from 60W to 130W), specifically designed for outdoor applications.
Most lamp driving solutions, both for HID and LED lamps, are based on a digital approach, and this is where the true intelligence comes in. An 8-bit or a 32-bit microcontroller handles all the functions needed to drive the lamp and, at the same time, manages all the data for implementing a smart street lighting network.
Moving forward along the key blocks of a smart street lighting system, let’s focus on the second sign of intelligence: Communication.
Networked street lighting systems can be managed via wired or wireless communications through a several proven communication standards. For the wired option, a digital control and monitor based on power line communication can be implemented. Enabling products range from power line transceivers to the latest generation of power line networking SoCs that support different modulations (B-FSK, S-FSK, B-PSK, Q-PSK, 8-PSK). For the wireless option, ZigBee technology can be used to build secure and reliable networks.
In both wired and wireless cases, the communication is bi-directional, and the monitored system can send and receive information and commands to and from the lamp.
Dimming levels and turn-on/turn-off commands depend on the time of day, road conditions, or the natural lighting conditions of the moment. This information, as well as that of lamp status, energy consumption of the lamp and its driving circuit, lamppost tilt, etc... can be collected on a cluster basis and sent to a central service center, where the data is monitored and commands are initiated.
The last block of a smart street lighting system we’ll discuss is smart sensing. What happens if a lamppost falls or is tilted away from its lighting position? No one might know until it is reported by a passer-by. The real-time detection of lamppost inclination or fall can be implemented using a MEMS sensor. In this case, an ultra-low-power, high performance, three axes linear “nano” accelerometer is ideal for the purpose. Interestingly, the same smart sensing technology that enables gesture recognition can improve a smart street lighting system to enhance road safety and reduce maintenance costs with a real-time, monitored schedule for service.
Figure 1: Smart street lighting system