In today's green, energy and cost conscious society, LED lighting is becoming the technology of choice in buildings, from homes and businesses to major municipal and industrial structures. For indoor lighting applications, the advantages of LED technology have now begun to outweigh the fact that the installation costs of traditional incandescent or fluorescent devices remains lower.
The key LED advantages include the ability to control lighting zones, to dim lighting levels, to turn lights on the instant they are required, and to combine with sensors for occupancy detection, to name a few. The LED evangelists’ message of reduced lifetime operating costs through lower energy use, and easier, cheaper maintenance is beginning to filter through to building managers and consumers. Additional benefits, such as improved safety, security, and comfort are also proving to be increasingly persuasive.
In new building projects, further cost savings are apparent when it is considered that solid state lighting, such as LED systems, require some two-thirds less headroom than conventional approaches, thereby reducing the height required between floor and ceiling. In a multi-story structure, this can amount to a significant saving in building materials.
A survey produced by Energy Smart Marketers shows that building contractors are now recommending LED lighting solutions in more than 70 percent of cases. In some countries, incentives are in place to encourage greater use of energy efficient lighting in new and refurbished building projects. The US EnergyStar program is an example. Smart city schemes, becoming prevalent throughout Europe and elsewhere, focus on initiatives to reduce peak power demand (as well as overall energy consumption), and lighting has been widely shown to be a major energy consumer in urban areas.
Right light, right time
Intelligent lighting is described as the ability to reduce the amount of light and/or energy used so that the optimum amount of light is delivered exactly where it is needed. Generally, high power, high brightness (HB), white LEDs are required for intelligent lighting and smart building applications. LED manufacturers, such as Osram, Cree, and Toshiba, are continuing to improve the brightness and consistency of whiteness. Characterization of whiteness has led to the development of neutral, warm, and cool white devices, designed for different applications. Dimmable systems are the norm, and power factor is an important consideration as power factor levels may be mandated by government, regional, or utility driven programs. Another key issue with digitally controlled intelligent lighting schemes is to ensure the system is easy to upgrade. Technology in smart buildings is advancing fast, and new applications are emerging, leading to changing customer expectations. The ability to upgrade the control software easily and even remotely is considered essential. (Figure 1)
Figure 1: Energy saving is the primary objective in smart building schemes, driven by government and utilities. Intelligent lighting can make a major impact on energy use. Photo credit: Power Integrations
Major cost savings can be accrued with LED lighting in the area of maintenance. LED devices typically last at least 25 times longer than the units they are replacing, and often as much as 50 times or even 100 times longer. Remote monitoring means that failed elements can be easily detected and located. From a design perspective, building contractors need to ensure that LED arrays and modules are designed for easy component replacement.
In the mood
For the future, the benefits of LEDs, such as easy dimming control and the ability to change the color within a system, will expand the applications and customer expectations of solid-state lighting. (Figure 2) Advanced LED technology, with more precise color binning, combined with sophisticated control techniques is already beginning to allow mood lighting features on a commercial scale. Lighting schemes may, for example, be switched easily from cool white lighting in an area used as a workplace, to a warm white lighting if that same area is later used for a social function.
Security lighting is likely to be an important application sector, where, by combining with motion sensors and ambient light sensors, for example, installations can combine both safety and power saving. Lighting in parking garages or car parks, for example, can be reduced dramatically if no one is detected in the vicinity. Lighting can clearly indicate to security personnel the presence of users or intruders.
Figure 2: LED lighting enables not only energy saving, but brings additional advantages of better control of lighting zones for comfort. Photo credit: Energy Smart Marketers
Although LED luminaires are considerably more efficient, with claims of up to 100 times the lifetime in some applications over traditional incandescent or fluorescent devices, they require specialized electronic control circuitry for thermal management and over-current protection. Essentially, LEDs convert most of the electrical energy they receive into heat rather than light. Therefore, without adequate thermal management, this heat can degrade the LED's life span and performance. The general design advice is relatively simple: keep the current through the LEDs constant and under the specified maximum.
Other articles in the Lighting TechZone focus on LED drivers, LED thermal management and over-stress control using current protection devices. A review of high brightness white LEDs, suitable for lighting applications, is also available in the TechZone.
The provision of 'platform-based' systems solutions is the underlying trend in the LED-based intelligent lighting market. Traditional electronics OEMs are creating subsystems of hardware and firmware to supply to building contractors and subcontractors. While mainstream LED manufacturers are, of course, dominating the market, supply chain partnerships are emerging, and systems and solutions are emerging from less likely sources. The driving attraction is the speed at which the lighting market is forecast to develop, combined with the requirement for increasingly sophisticated electronic control systems, and that lighting contractors are less likely to be able (or inclined) to build systems from scratch.
Electronics technology facilitates the ability to monitor and control all lights in an application, remotely or automatically, to turn them on or off, and to dim them; all of which is important. The ability to upgrade systems, adding new features and functionality, like many other modern electronics-based applications, is inherent in the digital programmability of electronics technology. In lighting applications, after the LED devices themselves, microcontrollers, wired and wireless networks, and sensors are proving to be the critical technologies to enable systems solutions.
Microcontrollers are ideal to take advantage of the unique characteristics of LED technology enabling the development of efficient, scalable and flexible designs for intelligent lighting. With digital control, designers can scale and easily adjust designs to suit specific applications. With a modular design using standard hardware and software elements, design reuse is maximized and design time is decreased. A digital approach also enables many innovative hardware features, such as soft start-up, delay, and PWM phase shifting, to be implemented in software, thereby keeping component count to a minimum.
Although traditional wired networks make sense in many buildings, new and affordable technologies such as mesh wireless networks have prompted innovative design opportunities in the commission of smart buildings. Wireless networks are also useful in refurbishing older buildings where adding or replacing wired networks might not be viable. ZigBee is proving to be a popular wireless protocol for lighting, particularly for applications requiring the control of large banks of uniform lighting zones.
Increasingly, lighting systems need to be connected to other networks via the Internet protocol (IP). In domestic applications, such systems could be controlled via a mobile digital device. Municipal or office buildings may also need to be controlled and monitored from a remote central location, as part of a smart city initiative, for example. In such cases, other Internet protocols may be more appropriate, such as the incoming 6LoWPAN, based on IPv6.
Integrating sensors into a lighting system requires some consideration. Providing power to the sensors may be straightforward in a new build, but more difficult in a retrofit situation. Battery power may suit devices that are required to perform simple tasks, such as detecting motion to indicate the presence of someone in a seldom-used room. Battery life might be 5 years in such situations.
Another option, being adopted in some of the smartest buildings around the world, is sensors powered by energy harvesting techniques. A growing range of companies are producing wireless products, such as sensors and switches, for managing HVAC and lighting energy consumption in buildings, based on the standard developed by the EnOcean Alliance. Powered by ambient sources of energy, such as light, heat, vibration and motion, the devices send radio signals via a wireless sensor network to automate energy conservation in buildings.
However, if sensors are required to provide instant updates on a constant basis, a permanent power source via a wired or power line network might be necessary.
For designers looking to enter the fast growing lighting market, there are a wide range of vendors and products to get started. Like any emerging sector, the vendor base is somewhat fragmented, with solutions based around different and multiple aspects of the overall system, including LED drivers, control circuitry, dimmers, connectors, microcontrollers and networking, as well as the LED specialists themselves.
Several traditional microcontroller specialists, for example, are providing modules, reference designs, and development kits for LED lighting schemes. These include Cypress Semiconductor, NXP, and Texas Instruments. Some systems solutions providers are from an analog and power background, such as Analog Devices, Allegro, National Semiconductor, and Power Integrations. Expanding into the systems solutions from a multi-technology base is TE Connectivity (AMP).
It has been widely reported that retrofitting solid state lighting into traditional systems is proving difficult in terms of maintaining the performance and efficiency associated with LED lighting schemes designed from scratch. Some companies have chosen only to offer solutions for new or replacement systems.
TE Connectivity, for example, is focusing its Nevalo platform on new system designs. The kit includes light modules, drivers with constant-current output, circuit-protection devices, dimming-control circuitry, optics, wiring systems, and software tools for thermal management evaluation and price vs. performance analysis. Users have a choice of more than 60 LED light modules in form factors for common lighting applications.
Texas Instruments offers a broad suite of microcontroller-based solutions for LED lighting design and control systems, plus demonstration platforms and development kits. Its TMS C2000™ Piccolo microcontroller DC/DC LED Developer’s Kit enables lighting designers to differentiate their designs with advanced features such as dimming, color tone adjustment, power line communication and fault detection. (Figure 3) The kit comes complete with the necessary open source hardware and software needed to start designing energy-efficient LED lighting systems for smart buildings.
Figure 3: Texas Instruments' TMS320C2000™ DC/DC LED Lighting Developer's kit.
In addition to the starter kits, TI offers a wide range of discrete components for OEMs to build their own systems, as well as partial solutions, combining controller, driver, and power factor correction circuitry.
TI has also just launched a sub-1GHz 6LoWPAN wireless network solution, aimed at providing a gateway for remote, low-cost wireless sensor networks, such as building lighting schemes, to connect to the Internet. It provides a wireless extension of wired IPv6 infrastructures, and, by operating in the sub-1GHz band, offers longer wireless range at lower power levels than traditional 2.4GHz-based 6LoWPAN offerings.
Cypress Semiconductor, meanwhile, offers support for a different lighting protocol. The DMX512 protocol allows designers to control complex lighting networks of controllers and dimmers in industrial buildings. Called EZ-Color™, Cypress Semiconductor's design solution for high-brightness (HB) LED intelligent lighting systems supports the control of up to 16 LED channels. The tool's proprietary firmware and optical feed back algorithms help designers ensure consistent color across multiple arrays of LED devices, and its PrISM modulation technology reduces low-frequency flicker and radiated EMI.
Cypress's PowerPSoC, shown in Figure 4, is an embedded power controller which aids system integration. It contains four channels of internal current sense amplifiers rated at 6 MHz, four 2 MHz hysteretic controllers independently configurable as buck, boost, or buck-boost, and four low-side n-FETs rated at 1 A, 32 V each, plus a 32 V internal input regulator.
Figure 4: A demonstrator lighting control solution using Cypress Semiconductor's PowerPSoC® High Brightness LED Controller and Power line Communication (PLC) solution
More recently, Cypress has announced support for the Power Line Communication protocol in its lighting applications with a combined power line transceiver and microcontroller solution. Based on existing copper power networks, and using a bus topology, it can be used to communicate data for control purposes, and is easily reconfigurable. Systems can be configured with capacitive touch sensitive panels or with a PC-based graphical user interface for intuitive and easy operation of complex systems.
This article has outlined how the intelligent lighting market is expanding fast in commercial, business, industrial as well as domestic applications, taking advantage of the benefits of solid-state lighting, specifically LEDs. It has outlined the important systems elements of digitally controlled lighting systems and considered illustrative examples of some of the wide range of systems solutions and partial solutions currently available. You can obtain more information by exploring the links provided to articles and vendor pages in the Lighting TechZone of the Digi-Key website.
- TechZone Lighting article: //www.digikey.com/articles/techzone/2011/aug/improving-the-efficiency-of-led-light-emission
- TechZone Lighting article: //www.digikey.com/articles/techzone/2011/aug/whiter-brighter-leds
- TechZone Lighting article: //www.digikey.com/articles/techzone/2011/sep/highoutput-led-module-systems-approach-for-downlighting-ssl
- Texas Instruments Lighting articles: http://www.ti.com/ww/en/lighting/index.htm