Internet of Things: Using Wireless-Controlled Lighting to Reduce Energy Costs
Lighting represents a significant fraction of electricity usage in residential and commercial buildings. According to the U.S. Department of Energy, lighting accounted for more than 13 percent of residential electrical usage and more than 20 percent of commercial electrical usage in 2013.¹Traditional mechanical wired lighting systems offer users few cost effective options in managing usage and controlling lighting expense. In contrast, wireless-controlled lighting allows households and building owners to tune lighting usage to more precisely fit lighting area and time-of-day requirements while simplifying maintenance and administration of large lighting systems.
Wireless-controlled solid state lighting offers substantial benefits, not only in managing energy consumption but also in providing a degree of flexibility and ease of use beyond that possible with traditional lighting approaches. For consumers and businesses, wireless lighting systems enable improved use of lighting resources despite continually changing requirements, while simplifying deployment of more sophisticated lighting and energy management strategies. For engineers creating these systems, a broad framework of silicon solutions and protocols helps simplify creation of low cost wireless lighting devices.
Lighting control applications that enable energy savings
In a typical wireless-controlled system, controllers or even personal smartphones communicate with these MCU-based luminaires, using two-way wireless communications to collect operational status and issue commands to the wireless lighting device. Along with basic on/off and dimming control, wireless-controlled lighting systems enable more sophisticated lighting management such as scheduling illumination levels at programmed times, controlling illumination based on room occupancy, and tuning both color and brightness to match the user's task, work area and preferences.
Beyond these user-directed features, these systems play a key role in supporting building management services and simplifying implementation of energy saving strategies. Wireless luminaires can perform self-diagnostic functions and transmit lamp usage reports and even warnings of potential failures to operators to help simplify maintenance and reduce cost.
For households and organizations looking to optimize energy costs, these systems can be designed to communicate to the smart grid to reduce load in demand-response arrangements. For example, during peak-rate hours, lighting can be slightly dimmed, reducing energy load and costs without users even noticing a significant change in illumination.
The composition of a wireless-controlled lighting device
In its most basic form, a wireless-controlled solid state lighting device combines one or more LEDs and its drivers with a microcontroller and wireless subsystem (Fig. 1). In addition, these devices also typically include sensors to monitor ambient lighting levels, temperature and occupancy needed to support more sophisticated lighting control applications.
Fig. 1: A typical wireless-controlled solid state lighting system combines an LED and its drivers with an analog front end, MCU and wireless interface. (Source: Texas Instruments)
The ready availability of a wide range of low cost MCUs with integrated RF transceivers has simplified development of wireless luminaires. For example, MCUs such as the NXP JN514x, Silicon Labs Si202x/3x, and Texas Instruments CC430F61xx, among others, combine an MCU core, on-chip memory, ADCs, peripherals, and RF transceivers needed to design sophisticated wireless lighting devices with few additional components beyond power and LED driver circuitry.
Fig. 2: At the heart of a wireless lighting device, an integrated MCU combines a CPU core, on-chip memory and digital I/O peripherals with an analog subsystem for sensor data processing along an on-chip RF transceiver for wireless communications. (Source: Silicon Labs)
Wireless lighting systems make sense (and cents!)
Wireless-controlled lighting offers an easier approach for deploying more effective lighting plans. Building owners can eliminate the cost of running expensive copper wire to each control point in a structure, simplifying installation in new structures and retrofits in existing buildings. Furthermore, these systems scale easily to serve larger areas, while providing needed flexibility to target specific zones with the right amount of illumination.
In some applications, such as street lighting where wired control is simply not practical, wireless lighting control provides features considered essential for proper operation. For example, in a string of street lights designed to turn on automatically as ambient light levels fall, the inability to synchronize operation results in spotty illumination at dusk when individual lamps turn on at different times as their individual photocells respond differently to changing ambient lighting levels. With wireless control, street lights can be synchronized to turn on simultaneously to cast uniform illumination from the full string of street lamps.
Communications in wireless lighting systems rely on protocols typically used in broader support for home and building automation systems. Some of these protocols include BACnet, Bluetooth, EnOcean, Insteon, JenNet-IP, ZigBee and Z-Wave. Bluetooth low energy (BLE) offers an increasingly popular foundation that can literally put sophisticated wireless control applications in the hands of consumers. Leveraging BLE connectivity built into most smartphones, tablets and other mobile devices, lighting developers can offer apps that combine ubiquitous wireless connectivity with familiar mobile interfaces to enable powerful lighting-control functionality.
Engineers can also find specialized wireless lighting protocols such as ZigBee Light Link, designed specifically for lighting applications. Intended as a global standard, ZigBee Light Link enables interoperability and wireless control of all components of a residential or commercial lighting network, offering capabilities including authentication and coexistence with other wireless channels. Underlying these protocols, RF communications for lighting applications use the standard ISM sub-GHz bands in regional markets or the 2.4 GHz band for global markets.
3: IP-based protocols such as NXP's JenNet-IP allow devices such as smartphones to directly address individual wireless lighting devices. (Source: NXP)
The ability to address individual luminaires offers a significant advantage in optimizing lighting resources to illumination requirements. IP-based protocols built on low level packet communications standards such as 6loWPAN allow direct communications between individual lighting devices and personal electronic devices such as smartphones. For example, a smartphone can communicate directly with an IP-based wireless-controlled lamp without the need for gateways or additional devices. Running in the luminaire's embedded MCU, communications protocol software stacks provide the necessary bidirectional communications services.
Wireless-controlled solid state lighting provides the flexibility and scalability needed to accommodate the need for energy management and the desire for illumination matched to the user's work area and personal preferences. Wireless lighting devices provide a cost-effective solution for implementing sophisticated solid state lighting applications, simplifying their deployment in homes, commercial buildings and outdoor applications. At the heart of wireless lighting devices, integrated MCUs combine analog front ends, digital peripherals, and RF transceivers, relying on a range of communications protocols to enable connectivity with users and other devices.
*U.S. Energy Information Administration, (2014). Annual energy outlook (DOE/EIA-0383ER (2014)). Retrieved from website: http://www.eia.gov/forecasts/aeo/er/tables_ref.cfm
Written By: Stephen Evanczuk
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