Wireless lighting control refers to over-the-air management of lamps or light fixtures using wireless communication technologies. Wireless control not only simplifies design, installation, commissioning, and operation of lighting systems, but it also provides a way for users to make a single environment flexible enough to accommodate various visual needs. Wireless lighting control is a plug and play solution, meaning there is no need for costly, complicated hardwiring as well as complex light management that uses traditional lighting control protocols. The transition from traditional lighting systems to connected solid state lighting (SSL) systems drives a whole new set of requirements for lighting control, especially around Internet of Things (IoT) which refined the concept of smart lighting.
Wireless Connectivity: the Blood Vessel of Smart Lighting
Smart lighting systems increasingly rely on ubiquitous wireless connectivity to transmit control signals. The digital nature of LED technology enables lighting products to become digital data nodes and allows them to participate in the Internet of Things. Smart lighting is no longer just about dimming or switching on/off in response to sensors and timers. While smart lighting continues to make use of control signals provided by local sensors and controllers, smart lights can be programmed to respond to application logic provided by online rules engines or can leverage data and environmental parameters collected from a host of interconnected devices such as fire/smoke/CO alarms, thermostats, HVAC controllers, security cameras, remote doorbells, humidity monitors, energy usage monitors, and smart utility meters.
At the most basic level, smart lighting is all about wireless connectivity. The ability of a connected lighting system to share information, facilitate interoperation and support interaction between a scalable number of lighting nodes is built on its wireless networking capabilities. Wireless networks don't just eliminate messy cables to reduce installation cost and enhance deployment mobility, they provide advanced interoperability that allows devices from different vendors or devices with different functionalities to exchange data. Today's smart lighting systems deal with how to integrate the various digital nodes into a collective whole. A high degree of interoperability among heterogeneous types of ever-increasing numbers of geographically dispersed sensors, devices and end points simplifies network management, enhances data transmission security, reduces the risk of device or manufacturer obsolescence, and makes the smart lighting infrastructure future proof.
Facilitating Automatic Lighting Control
Smart lighting is essentially a convergence of wireless networking and automatic lighting control. There are a variety of lighting control strategies that are designed to deliver the correct amount of light and/or the desired lighting effect, where you want it, when you want it. Dimming, occupancy control, daylight harvesting and time scheduling are the most commonly used strategies.
Dimming control allows adjustment of light intensity of a light source. Dimming effectively reduces energy consumption and supports designs where complex layers require careful balancing of luminous contrast layers. The most commonly used control methods used to dim LED loads include 2-wire forward phase (leading edge), 2-wire reverse phase (trailing edge), 3-wire forward phase (leading edge), 4-wire 0-10VDC, 4-wire DALI (Digitally Addressable Lighting Interface), and pulse width modulated (PWM) dimming. In smart lighting applications, dimming is typically not used as a stand-alone lighting control feature. It works in tandem with following automatic lighting control strategies to provide intelligent dimming control.
Occupancy control strategies use microwave, passive infrared (PIR), or ultrasonic sensors to detect the presence of an occupant and accordingly signal a connected controller to turn lights on or off and adjust the light output. Microwave detectors emit high-frequency electromagnetic wave (5.8GHz) and measure the change in the reflections as the signals bounce off moving objects. PIR sensors detect heat radiation of moving objects. Ultrasonic sensors detect a frequency shift in the emitted and reflected ultrasonic waves.
Daylight harvesting is a strategy to dim or switch lights when natural daylight detected by a photosensor in an area is higher than the threshold value.
Time scheduling uses a time clock or software-based intelligence that is built into the light controller to trigger pre-set on/off or dimming control.
The complete suite of smart lighting features can only be enabled when the sensor- or logic-embedded lighting nodes are able to communicate. Wireless sensor networks (WSNs), as a critical part of the IoT architecture, collect data about the environment and communicate it to gateway devices which relay the information to and from a centralized cloud platform over the Internet. The WSN delivers data-driven intelligence from a central network server to smart lights, enabling lighting control strategies to be executed in a truly smart way.
How Wireless Lighting Control Works
When we talk about wireless control, it's not about wireless control signals transmitted through the air using wireless infrared (IR) energy. Wireless lighting networks typically operate at a radio frequency (RF) between 100 MHz and 5.8 GHz. A lighting infrastructure that use radio wave for device communication typically consists of these components:
- A driver (for LED lighting) that translates the effect of the control signal into corresponding light output.
- A controller that assigns commands to the driver to execute a lighting change. It receives input from connected sensors or from the network server via a gateway.
- A wireless communication module that is usually integrated with the controller to provide two-way communications.
- A gateway or hub that acts as an intermediary to relay messages between lighting devices and a central network server.
- A network server that handles all the intelligence and complexity associated with managing the lighting network.
- A software platform that acts as a mediator between the hardware and application layers. It provides an interface to initiate data and device management.
In the context of Internet of Things, wireless lighting control is implemented at the physical and network layers. The physical layer (or device layer) defines the electrical and physical specifications of the data connection as well as the protocol to establish a connection between lighting devices. Also known as transmission layer, the network layer is responsible for securely transferring data packets between lighting devices and the network server or information processing system.
Wireless lighting systems typically have a device-to-gateway architecture in which the physical layer communicates with application layer via network layer. The application layer provides centralized device management and realizes various practical applications based on the information processed in the software platform. The gateway at the edge of the network establishes secure wireless connections with multiple lighting points and connects to the network server via standard IP connections. As you can see, the gateway must provide protocol translation to mediate the communications between the physical layer and application layer.
Aside from device-to-gateway communication model, device-to-device wireless communication becomes increasingly important in industrial IoT lighting applications. Sometimes referenced as M2M (machine to machine communication), device-to-device communication allows smart lights to talk to one another and exchange the data through routing and forwarding, without the need of protocol translation nor advanced data processing. Local interactions between lighting points through wireless PAN networks enable collaborative operations that open up further possibilities to increase automation.
For wireless lighting to thrive, a robust connectivity topology is crucial. Topology describes the interconnections of lighting nodes in a network. The topology of a wireless lighting system makes all the difference when it comes to reliability, resilience, transmission distance, communication rates, and numbers of nodes. The two fundamental network topologies for wireless lighting systems are star and mesh. In a star topology, a central node managing connections with many peripheral lighting nodes. The central node is the hub, or access point (AP), that connects to the internet. In a star topology, peripheral nodes do not talk to each other unless the central node forwards the message.
The mesh topology is an interoperable networking solution that can extend a network range through multiple hops and offers excellent scalability and reliability. In a mesh network, nodes are all connected to each other. Each node has processing power and memory to support the routing function. This allows the intelligence of a lighting system to be replicated in every node and, in such a way, avoids the single-point of failure issue that typically happens on wireless networks using a star topology.
A communication protocol is formalized set of rules and guidelines for the interactions among the network's interconnected nodes. It defines the data exchange formats and routing rules of packets from source to destination, describes how to transmit every bit of data, and tells what is the frequency of radio waves. Today, a typical smart lighting systems consists of a router/gateway with an array of lights being connected to the internet using various wireless communication protocols. A router can be defined as a device that connects networks only if they use the same protocol and address format, whereas a gateway is designed to converts addresses and translate protocols to connect different networks. Wireless connectivity solutions can be grouped into three categories: low power short range technologies such as Bluetooth Low Energy (BLE), ZigBee, Z-Wave and Thread; lower power long-range or wide area network technologies like LoRa, Sigfox, LTE-M, and NB-IoT; and high power wireless broadband protocols such as Wi-Fi and 4G/5G.
Bluetooth Low Energy (BLE)
Bluetooth Low Energy (BLE) is a wireless personal area network (PAN) technology optimized to transport very large amounts of very small data packets. It is a packet-Based protocol based on spread spectrum signal structuring. Bluetooth operates at 2.4 GHz with a range of 40-240 meters and a maximum data rate of 50Mb/s. Unlike other low power radio solutions that hop to a hub or a gateway to collect and distribute commands or data, the Bluetooth network relies on its nodes to relay messages from the source node to the destination. While Bluetooth was originally developed for point-to-point device connections, Bluetooth Mesh which provides many-to-many networking capability for large-scale device networks bring simplicity, scalability and interoperability to wireless lighting controls.
ZigBee is an open, global wireless standard designed to address the unique needs of low-cost, low-power wireless M2M network. Built on top of the IEEE 802.15.4 MAC and physical layer, the packet-based radio protocol uses destination-based routing to deliver packets and supports both full function devices (FFD) and reduced function devices (RFD). ZigBee operates in unlicensed industrial, scientific and medical (ISM) radio bands: 915 MHz in US and Australia, 868 MHz in Europe, 784 MHz in China, and 2.4 GHz in most jurisdictions worldwide. ZigBee supports both mesh networking for maximum outing flexibility and multicasting for multi-node message delivery with a single transmission. A ZigBee network architecture consists of three logical components: the ZigBee Coordinator (ZC), ZigBee Router (ZR) and ZigBee End Device (ZED). Data transmission rates of ZigBee networks vary from 20 kbps in the 868 MHz frequency band to 250 kbps in the 2.4 GHz frequency band.
Z-Wave is a low-power, low-latency communication technology that operates on a single channel in the 868 MHz band for Europe and 915 MHz band for North America and Australia. This communication protocol supports full mesh networking without requiring a coordinator node. Z-Wave employs a source-based routing scheme and can route messages via up to 4 repeating nodes. The maximum number of controller and/or slave nodes that can be supported by a single network is 232 nodes, with variable data rates from 40kbps up to 100kbps, depending on the generation of chips. Operating in the sub-1 GHz band gives Z-Wave networks excellent immunity to interference from the networks in the 2.4 GHz band. Z-Wave has better interoperability and lower interference than ZigBee, whereas ZigBee has a faster data transmission rate and unlimited hops between the controller and the device.
Thread is an open, IPv6-based, low-power mesh networking protocol that runs on top of the well-known radio standard IEEE 802.15.4 specification and operates in the 2.4GHz ISM band. It supports data rates up to 250 kbps and connects up to 250 nodes every network. The device types in a Thread system architecture include border routers, routers (gateways), router-eligible end devices (REEDs), and sleep end devices. Thread makes full use of 6LoWPAN's fragmentation and reassembly mechanism to efficiently transmit packets over the 802.15.4 network. The Thread stack supports full mesh connectivity and dynamically reconfigure itself in response to any failures thanks to the use of Mesh Link Establishment (MLE) protocol. Thread supports low latency (less than 100 milliseconds) and therefore enables a wireless network to support more devices.
Wireless Fidelity or Wi-Fi is the go-to standard for smart home setups and applications involving large amounts of data movement across a wireless network. This local area networking (LAN) technology is designed to handle large amounts of data traffic. The Wi-Fi technology is based on the family of wireless networking standards which define many specifications for Wi-Fi LANs. The 802.11a standard which operates in the 5 GHz band supports up to 54 Mbps. The 802.11b standard uses direct-sequence spread spectrum (DSSS) and provides up to 11 Mbps transmission in the 2.4 GHz band. The 802.11g standard which inherited the advantages of 802.11b and 802.11a supports connections up to 54 Mbps in the 2.4 GHz band. 802.11n which is a further enhancement of 802.11g utilizes both the 2.4Ghz and 5Ghz bands. It has a 300 Mbps data rate. The 802.11 ac standard supports simultaneous connections on both the 2.4 GHz and 5 GHz bands with a 1300 Mbps data rate in the 5GHz band and 450 Mbps data rate on 2.4 GHz band. Wi-Fi has an RF range of up to 100 meters (328 feet). Wi-Fi is implemented in all laptops, tablets, smartphones and TVs, making it logical to leverage this ubiquitous infrastructure. However, Wi-Fi is too resource-intensive. It star topology, which means that all its nodes connect directly to a wireless router, may cause single point of failures if the router goes down.
LoRaWAN is a Media Access Control (MAC) protocol that uses Chirp Spread Spectrum (CSS) modulation at its physical layer known as LoRa (Long Range). This low power wide area network (LPWAN) protocol uses the sub-GHz ISM bands (433 MHz and 868 MHz in Europe, 915 MHz in the US, and 430 MHz in Asia) to provide high signal permeation and wide coverages. A LoRaWAN network architecture includes three types of physical devices: end device (ED), gateway (GW), and network server (NS). The LoRaWAN specifications define three functional classes for end devices, namely, Classes A, B, and C. LoRaWAN network architecture typically has a star-of-stars topology in which the gateway acts as a bridge that relays messages between edge-devices and the central network server. Each edge device can connect to multiple gateways by using single-hop wireless communication. This topology enhances signal decoding performance and creates a reception diversity gain. LoRaWAN communicates with a date rate ranging from 0.3 kb/s to 50 kb/s, and has a transmission range of up to 15 km.
Sigfox is a proprietary low power, long range LPWAN solution that uses a technology called Ultra Narrow Band (UNB). Sigfox employs a DBPSK scheme for uplink modulation and a GFSK scheme for downlink modulation. The ultra-narrowband radio technology operate at 868.00 to 868.60 MHz (uplink frequency band) and 869.40 to 869.65 MHz (downlink frequency band) in Europe. At the expense of much reduced data packets Sigfox consumes only 50 mW of power - 1% of the power used through cellular communication. A Sigfox device can only transmit maximum 12 bytes per payload, and maximum 140 messages per day. The protocol hops across frequency bands to mitigate interference. Hence Sigfox is well suited for low-bandwidth and low-frequency applications where the networks only needs to handle small amount, infrequent bursts of uplink data transmission.
Ingenu is a preparatory LPWAN technology which works in the 2.4 GHz band. Despite the fact that operating in the 2.4 GHz band leads to a shorter range than Sigfox and LoRa, the robustness of physical layer design provides long range propagation and excellent coverage under the most challenging RF environments. The Ingenu solution uses Random Phase Multiple Access (RPMA), a patented direct-sequence spread spectrum modulation technique, to enable higher data throughput rates (50x other LPWA solutions) and provide a secure, wide-area footprint. Excellent broadcast capability and minimal overhead combine to give Ingenu networks high scalability, allowing control commands to be sent simultaneously to a significant number of devices. However, this technology requires more processing power and has higher system complexity than other solutions.
NB-IoT (Narrow-Band IoT) is a low power area (M2M) network solution that operates in licensed frequency bands and provides data rates similar to LPWA technologies. NB-IoT can operate at a system bandwidth as narrow as 180 kHz and supports both single-tone (with 3.75 kHz or 15 kHz spacing) and multi-tone SC-FDMA (with 15 kHz spacing). The 3GPP standards-based technology exploits both the LTE spectrum and the idle cellular spectrum re-farmed from current cellular systems. NB-IoT, which uses the LTE/4G physical layer, provides a better data rate performance, higher quality of service (QoS), better network ranges, and lower latency than the LoRa technology. Although LoRa outweighs NB-IoT in terms of power efficiency, spectrum and deployment cost, NB-IoT is often preferred for IoT applications where relatively higher data rate is essential.
LTE-M, also known as LTE Cat M1 or Long Term Evolution for Machines, is a variant of the existing 4G networks. It offers transmission range, data rate, availability, security and managed M2M communication comparable to NB-IoT. This low power version of LTE enables IoT devices to connect to a 4G network directly and allows fairly large chunks of data to be transmitted. By using techniques called extended Discontinuous Repetition Cycle (eDRX) and Power Saving Mode (PSM), LTE-M allows IoT devices to have longer sleep cycles and awaken only to transmit or receive data. Advanced power management enables IoT devices to operate for at least 10 years of battery life.
How Smart Devices Connect to Lighting
The marriage of LED lighting and the Internet of Things rides on the huge success of smartphones and tablets which can be used to exchange data and enable interaction between sensors, actuators, and the Internet. While a smartphone can directly connect to an LED luminaire equipped with a Bluetooth sensor, in networked smart lighting systems it acts as an application layer gateway device that provides an intermediary between lighting nodes and cloud. The smartphone runs an application software known as a mobile app to communicate with smart lights and relay data to the cloud via IP networks. Smart lighting isn't just about wireless connection and control with smartphone or tablet apps. Smart lights can be wirelessly operated by voice activated smart controllers which run Amazon Alexa, Google Assistant, Apple HomeKit, Microsoft Cortana, or other cloud automation platforms. These smart speakers provide gateway services to control lights with the power of voice.