Energy Conservation Utilizing Wireless Dimmable Lighting Control in a Shared-Space Office Yao-Jung Wen Department of Mechanical Engineering, University of California, Berkeley
[email protected]
James Bonnell Department of Mechanical Engineering, University of California, Berkeley jbonnell@ berkeley.edu
Alice M. Agogino Department of Mechanical Engineering, University of California, Berkeley agogino@ berkeley.edu
Abstract – Overhead light fixtures in shared-space offices are typically grouped into banks, each of which is controlled by a single switch. Even in offices with daylight responsive systems, the luminaires are divided into zones controlled by one photosensor per zone. Too often, the geographically-defined “zone” does not correspond to occupied areas, and energy is wasted illuminating the unoccupied areas. Research has also shown that people have diverse preferences for lighting and that optimal personal lighting is highly correlated to productivity. Systems that deliver identical lighting can compromise personal preferences. Various researchers have pointed out that individual light control can increase both user satisfaction and energy efficiency. The main obstacles are the exorbitant initial cost of long-distance rewiring and the lack of efficient control. Leveraging the emergence of wireless sensor/actuator network technologies, we developed a module interfaced with a dimming ballast to enable individual, dimmable light control. As a pilot implementation, the modules were installed in a shared-space office with 19 luminaires without out-of-fixture rewiring. Occupants were allowed to set their preferences and given the ability to override current light settings through a dedicated webpage. A kiosk was set up by the entryway so occupants could easily select their preferred lighting when entering the space. A short term energy monitoring revealed a 46% energy savings even though there was no window in the office to facilitate daylight harvesting. The occupants were also satisfied with working under their preferred lighting.
1 INTRODUCTION A branch of research involving office lighting has been focusing on the impact of individual control of electric lighting on energy savings and user satisfaction. A variety of laboratory studies (Newsham et al. 2008; Newsham et al. 1998; Veitch et al. 2000) and field studies (Boyce et al. 2006; Jennings et al. 2000; Maniccia et al. 1998; Moore et al. 2002) have revealed positive results in energy savings and increased satisfaction if occupants are allowed to control the lights. These studies were typically conducted in carefully controlled environments with well designed lighting systems, room interiors, furniture locations, and number of occupants allowed to control the lights in order to extract pertinent information from the variables of interest. Built on the promising results concluded from published studies, our research emphasizes the more practical aspect of enabling individual lighting control that was seldom tackled in previous studies. Specifically, this paper targets lighting systems in shared-space offices and attempts to answer the following three questions. (1) How can a lighting system be converted into individually controllable lights with minimum effort and cost for offices in both legacy buildings and new constructions? (2) How to provide a control mechanism that can serve all the occupants in an office as opposed to only one or two subjects in the designed studies? (3) How will the energy savings and user satisfaction differ from those reported in the controlled laboratory and field studies? To answer the first question, this research adopted the emerging wireless sensor/actuator network technologies to mitigate the high retrofitting cost by replacing traditional wiring requirements with networked radio links. A wirelessenabled actuation module was developed for interfacing with dimming ballasts and easily integrated into regular lighting
systems. The second question was answered by taking advantage of the wired and wireless Ethernet, which exists ubiquitously in every office nowadays, such that all occupants could control each of the luminaires through a dedicated website from their own computers. A local server built exclusively with free open-source software bridged the wireless actuator network, the lighting system, and the occupants. The system requirement of the local server was no more than the capability of a common PC on the market. Although the local server currently coordinates individual lighting actuation, it is designed to easily incorporate additional lighting control technologies. A pilot implementation of the developed lighting system in a medium shared-space office with 19 troffers was realized to answer the third research question. From the observations and informal interviews of the real occupants who work in the office on a daily basis, the user satisfaction with individual controllable lighting was consistent with the findings in previous studies. Not only did we realize significant energy savings, but also increased user satisfaction through their ability to customize lighting for their specific current tasks.
2 ENERGY SAVINGS VS. LIGHTING PREFERENCES Buildings are responsible for more than one-third of the total primary energy consumption in the US, while two-thirds of a buildings energy needs are electrical (The Interlaboratory Working Group 2000). Lighting accounts for 25% of the primary energy use in commercial buildings, and thus dominates the possibility of energy savings (The Interlaboratory Working Group 2000). 25-40% potential savings may be achieved by means of modern lighting control technologies (Mills 2002), such as daylight harvesting, load shedding, scheduling, etc. It is common to almost all of the lighting control technologies to divide an office space into zones and enforce identical control on luminaires in the same zone. The definition of the zone may be determined by how the luminaires are electrically wired or by similar amount of daylight received. It has been widely acknowledged that people have diverse preferences in lighting, and the ideal lighting condition may vary significantly from person to person (Tregenza et al. 1974; Veitch et al. 2000). Studies also reveal that lighting satisfaction is highly correlated to the mood and productivity of the occupants (Dilouie 2003), and people do appreciate, and even demand, a certain degree of lighting control over the environment in which they work, no matter how smart the lighting system may be (Boyce et al. 2006; Dilouie 2004). This makes it extremely hard to design the lighting for a shared-space office that satisfies all the occupants while still maximizing energy efficiency. Patents exist for individual control of lighting fixtures via various communication technologies including power line and infrared (Hakkarainen et al. 1997; Lansing et al. 2000; Mier-Langner et al. 2002; Ranganath et al. 1995). Also, several researchers have shown that it was not only energy efficient but also highly satisfactory to the occupants when allowing individual lighting control in offices (Embrechts et al. 1997; Moore et al. 2003; Newsham et al. 1998). Although this approach is a solution to find the equilibrium point between energy efficiency and occupants’ lighting preferences, no concrete idea has been proposed as to how to make the transition from laboratory setting for one or two subjects to practical applications. The main challenges lie in the cost and complexity of rewiring and lack of efficient mechanisms for delivering personalized lighting. This research leverages the emerging wireless sensor network technologies, and demonstrates a concrete idea of facilitating individual light control while minimizing the retrofitting effort through an implementation of a shared-space office with 19 luminaires. During this work a stand-alone system was developed for enabling individual lighting control; however, the ultimate intention is an automatic lighting system where the luminaires can be individually controlled for increased occupant satisfaction, concurrently utilizing energy efficient control strategies such as daylight harvesting, loadshedding, etc.
3 WIRELESS SENSOR AND ACTUATOR NETWORK TECHNOLOGIES The idea of ‘Smart Dust’ wireless sensor networks was first proposed by a research team in UC Berkeley in 1999 as a futuristic mesh network comprised of dust-sized processing and communication units based on MEMS technology (Pister et al. 1999). While truly miniature platforms are still under development, millimeter-scale ‘motes’ and the surrounding network technologies are maturing over the past years, and are now commercially available (Crossbow Technology Inc. 2007; Moteiv Corporation 2005). Several generations and variations of smart motes exist, yet all consist of a microcontroller with limited memory and a wireless communication unit. These units can be configured with a variety of sensors and deployed in high-density, distributed sensor networks. Recently, researchers have expanded initial
implementations involving data gathering alone, to a mixture of sensing and actuation within the same mote network (Akyildiz et al. 2004). Wireless technologies have been considered as a promising solution for advanced building operation systems to circumvent costly installation and rewiring, particularly in legacy buildings (Kintner-Meyer et al. 2004). Researchers have attempted to apply wireless sensor networks in place of the traditional ceiling-mounted photosensors while retaining similar or even higher energy savings than conventional daylight responsive systems (Granderson et al. 2004; Singhvi et al. 2005; Wen et al. 2004; Wen et al. 2006). Recently, a few researchers are focusing their attention towards interfacing this wireless network technology with emerging high efficiency lighting actuation mechanisms (O'reilly et al. 2005; Teasdale et al. 2006; Wen et al. 2006). This research is in its very early stages, and not many results have been reported to the authors’ best knowledge. The wireless mote platforms used in our research are the Tmote Sky manufactured by Moteiv Corporation as shown in Fig. 1. Each mote contains an 8MHz microcontroller, a 2.4GHz IEEE 802.15.4 wireless transceiver, several 12-bit ADC (analog-to-digital converter), DAC (digital-to-analog converter) and general I/O (input-output) ports (Moteiv Corporation 2006). They are loaded with TinyOS (Levis et al. 2005), an operating system specialized for wireless embedded sensor networks, with customized programs specifying their behavior suitable for this research.
Fig. 1. Tmote Sky wireless platform (Moteiv Corporation 2006).
4 SYSTEM ARCHITECTURE The system is comprised of luminaires equipped with wireless-enabled actuation modules interfaced with dimmable ballasts, a local server in charge of controlling and monitoring the lights, and client web browsers for bridging the occupants and the system. The system architecture is shown in Fig. 2. The information flow is bi-directional between the client web browsers and the local server and between the local server and the luminaires. The route from client web browser through the local server to the luminaires is for actuation activities, while that from the luminaires via the local server to web browsers is for status feedback.
Fig. 2. Lighting system architecture.
The occupants may set/resume their preferred light levels or interact with the lighting system real time through a designated web page, which can be accessed via any web browser or network-enabled devices such as desktop PCs, laptops and PDAs. The multi-functional local server is composed of a web server, database, lighting control program, and wireless mote base station. The web server provides the web control interface to the client-side browsers and bridges the control application program. It also communicates with the database for authentication of the users in order to prevent the system from being tampered with by unauthorized users. The control application program parses the requests from client-side and responds accordingly. It stores the occupants’ preferred settings in the database, retrieves the users’ preset settings from the database, and generates and passes actuation command packets to the mote base station. In the meantime, it also processes the packets forwarded from the mote base station. The incoming packets contain status reports from the individual actuation modules, which are then logged into the database and compared against the expected status of the system. The actuation module connected to the dimming ballast is integrated with a wireless mote platform. The mote processes the received wireless packets and translates the actuation commands into 0-10VDC voltage signals to dim the lights or toggle the relay on the actuation module to turn the lights on or off. The mote also periodically sends back its own actuation status to the base station.
5 PROTOTYPE HARDWARE AND SOFTWARE Several key hardware and software elements were developed for realizing the system. The hardware is the mote-based actuation module, and the software includes the construction of the local wireless server, the web interface, and the embedded software on each mote to determine the behavior of each actuation module.
5.1 MOTE-BASED ACTUATION MODULE The actuation module was developed with two objectives in mind: to enable the self-configuring wireless communication capability of the luminaires and to minimize the retrofitting cost and complexity. The resulting prototype used in the implementation is shown in Fig. 3. The actuation module is installed between the dimming ballast and the mains via five wires, eliminating any need for out of fixture re-wiring. The 277V line is stepped down, rectified, and regulated to the voltages that are required to power the mote and dim or toggle the light, as depicted in the block diagram shown in Fig. 4. Since the mote is always powered, the limited-energy issue typical with other wireless sensor networks powered by batteries is non-existent.
Fig. 3. Mote-based actuation module.
Fig. 4. Block diagram of the actuation module. The mote platform sitting on the actuation module is programmed to listen to the network for actuation commands, report back its current actuation status to the local server, and coordinate with other motes to form a multi-hop network. Upon receiving an actuation command addressed to it, the mote transforms the specified dimming level to an analog signal with the onboard DAC. This signal is then amplified to a 0-10V voltage signal to set the level of the dimming ballast. If the command indicates to switch the fixture on or off, the mote will instead toggle the relay on the module with its general I/O port. The mote also periodically generates packets containing its current status and sends them back to the base station on the local server. The purpose for the status feedback is twofold: to monitor the actuation status, and hence energy usage of the entire system, and to reinforce the wireless network links and compensate for lost or corrupted actuation packets during wireless transmission. Furthermore, the motes will autonomously configure themselves into a network by identifying their parent mote in the route to the base station as soon as they are powered up. The network is dynamic and periodically updated to avoid bad or interrupted communication links.
5.2 LOCAL SERVER The local server is an integration of five subcomponents: a database, a web server, a control application program, a watchdog function, and a mote base station. Each of the elements was implemented with free open source software in view of zero-overhead, compatibility, and scalability. The database is linked to the control application program, and stores user accounts, user lighting presets, and actuation and status feedback history for each actuation module. The web server serves as a bridge between the users and the control application program. The graphical user interface is in the form of a website, and only users with records in the database table will be granted access to the user interface in order to prevent unauthorized access to the lighting controls. Through this web interface occupants can specify their preferred light settings, resume one of their presets, or override the current setting. A secondary script runs parallel to the main application serving as a watchdog function. Should any of the remote parts of the system (such as the primary login screen) not report at their regular interval, the system administrator will be emailed immediately. While this script serves strongly as a debugging agent for the purposes of this implementation, the functionality can easily be expanded, as will be mentioned in the future work section. The mote base station is composed of a mote plugged into the USB port of the computer and listening to the wireless network. This base station serves as the bridge between the wireless actuator network and the control application program. The control application program is the center of the system where the actuation requests are processed and actuation commands are issued. The main task of this program is to take in the actuation requests, which could be in the form of user presets or real-time overriding, from the client-side website, retrieve necessary information from associated tables in the database, and translate the request into actuation command packets for wireless transmission. Each time an actuation command is generated, a corresponding entry will be logged into the associated table in the database. In order to account for possible interruption or corruption of the wireless network communication, the program also listens to the status feedback from the actuation motes, compares the status to the most recent actuation history, and resends the actuation
packet if any inconsistency is detected. In addition, the program parses the users’ preferred settings and stores the presets into the proper table in the database, which can then later be retrieved when the occupants request to resume their presets. In addition to the current setup for coordinating individual lighting control, the server was designed to be ready for future extension into a fully automatic lighting system. The mote base station also listens to and forwards messages from other sensors and actuators which can be expanded to include photosensors, occupancy sensors, etc. Additional lighting management strategies, including daylight harvesting, scheduling, occupancy sensing, load shedding, etc. can reside in the control application program.
5.3 WIRELESS NETWORK DESIGN Two separate wireless network routing mechanisms are implemented for the outgoing versus the incoming communications. The outgoing traffic, the actuation messages from the base station to the actuation motes, adopts a flooding mechanism. This is a broadcast-based mechanism where the message originating from the base station will be sent to specific motes, but all other motes will concurrently act as relay stations, forwarding the message until it reaches its intended destination(s). This mechanism allows not only one-to-one but also one-to-many and one-to-all communication. This results in efficient message sending to groups of motes with a single command packet. The incoming traffic utilizes a unicast, tree-based mechanism. This is a robust unicast communication model with hopby-hop acknowledgement for the status messages to be sent from each actuation mote back to the base station. A routing tree is established upon system power-up, and periodically updated based on network conditions to maintain the most efficient route for message passing to the base station. The base station initiates the configuration of the routing tree by broadcasting a beacon periodically, at which point the actuation motes will try to identify and update their parents accordingly. An intermediate mote along the route will acknowledge to its child when receiving a packet and forward the packet to its parent towards the root of the virtual tree: the base station. An unacknowledged packet will be resent from the child to its parent. This mechanism establishes a multi-hop wireless mesh network for efficient low power communications and extended ranges beyond the capabilities of one mote alone.
6 PILOT IMPLEMENTATION The prototype system was implemented in a shared-space office in an educational research building over 20 years old. The office contains a hallway, a group meeting area and a work area with 12 personal workstations. The 817 square foot office space was lit by 19 2-lamp fluorescent light troffers originally configured to be controlled by a single switch. The office was located in the interior of the floor, and hence had no windows. This helped in simplifying this pilot implementation by not having to consider the light contribution from daylight. Extending the system to account for, and harvest daylight, will be discussed in section 8. The implementation method was designed around minimizing the amount of costly retrofitting, while still achieving full functionality. Retrofitting simply included replacing the original ballasts with dimming ballasts, installing the motebased actuation modules in the troffers, and replacing the original T12 lamps with T8 tubes. Two professional electricians, who belong to the staff in charge of campus-wide lighting maintenance, were recruited for the retrofitting task. Both electricians had worked with dimming ballasts before, but neither of them had prior experience with this particular motebased actuation module. It took each of the electricians roughly one hour to complete retrofitting of the first luminaire, but the retrofitting time reduced to about 20 minutes per troffer for each electrician after they got up to speed and had developed their own method for installing the module. The wires used on the actuation modules were color coded to match the color of the wires used for typical dimming ballasts and power lines to avoid confusion and enhance the ease of installation. The local server was set up at the far back of the office, while the main log-in screen was hosted on a kiosk located directly on the inside of the single entryway to the office space. The location of the server was initially chosen for convenience based on where a pre-existing server was available, however, this location proved particularly advantageous since it was adjacent to a location where power measurements for the whole room could be taken. The server position enabled the base mote to be about three feet from the floor with line of sight to almost all of the luminaires. Since all of the user interfaces were implemented with a mixture of Java and HTML with PHP scripting, the kiosk at the entryway simply had to have browsing capabilities. The kiosk was a touch screen computer running a generic web browser. To minimize the disruption in adopting the new system, a simple one-click login method was used in the interface. A sample of this screen can be seen in Fig. 5.
The occupants, who were mostly graduate students and researchers, were given a half-hour presentation that walked them through how to create a user profile, set lighting preferences, and override current light settings with the full web interface. This was made available to any computer within the lab space after logging in as an authorized user. As soon as the occupants created their profile, their name showed up automatically on the kiosk machine along with their custom named locations. For this initial deployment, to minimize the complexity of conflicting lighting preferences in overlapping space, the light controls for any given light were considered additive. Should any conflict arise, the greater of the two values would be used. The assumption in this method is that people will be more willing to accept working under a brighter, rather than a dimmer lighting condition. Optimizing conflicting personal preferences is a non-trivial research question beyond the scope of this implementation. Related research tackling this problem is under development and will be briefly discussed in the later section.
Fig. 5. Section of In/Out kiosk screen.
7 IMPLEMENTATION RESULTS In order to rigorously determine the energy consumption and the usage patterns, a customized power measurement instrument was installed exclusively for this purpose. The measurement was processed and entered into the system database. This power measurement instrument was calibrated against a high-fidelity ELITEproTM power meter by Dent Instruments for the first three weeks after the system was up and running. The power consumption of the lighting system during the period February 10, 2008 to March 20, 2008 was analyzed to determine savings. Fig. 6 shows the average hourly usage pattern of the office, where the percentage of usage means the percentage amount of time in each hour during the analyzed period when the office was occupied by at least one person. The average hourly power consumption of the new lighting system is shown compared to all on/off operation with the same ballast in the histogram in Fig. 7. This theoretical all on/off operation was determined using the same office light usage data, but assuming that the lamps were operated only all on (rated as the full energy consumption of the ballast) and off (zero power). In this sense, the comparison is taking into account the overhead of the motes and the actuation module in each of the retrofitted troffers. The input power of the ballasts used in this calculation is the maximum power of the new dimming ballast instead of the less energy-efficient non-dimmable ballasts that this system replaced. This choice was made to eliminate the difference in efficiencies between the old and new ballasts. The usage data is also presented in average hourly format in Fig. 8. The calculated power consumption comparison by hour can be seen in the histogram in Fig. 9. The savings from enabling individual control of lights and personal preference setting in this case is 46%. The occupants of the office knew beforehand that the lighting system would be retrofitted, but didn’t know exactly how it was going to be operated and configured. In other words, the introduction of this system was totally new to them. Since the number of people working in this office and using it on a daily basis was fixed and limited, a rigorous human satisfaction test was not conducted. However, according to the preference settings and informal interviews with the occupants, they all showed appreciation for, and actively took advantage of being able to set their own preferred lighting. Some users with strong energy awareness explicitly expressed their admiration for being able to conserve energy by turning off unnecessary lights in unoccupied areas.
Fig. 6. Office percent usage by day of week.
Fig. 7. Power consumption comparison by day of week.
Fig. 8. Office percent usage by hour.
Fig. 9. Power consumption comparison by hour.
8 DISCUSSION AND FUTURE WORKS The 46% energy savings gained in the pilot implementation appears to be larger than studies conducted by other researchers (Embrechts et al. 1997; Moore et al. 2003; Newsham et al. 1998). This may be because approximately onethird of the office was a group meeting area, which was not in use as often as the personal workstations in the rest of the office. This large area can now be unlit as compared to the pre-retrofit configuration. Also, the occupational nature of the users led to some extended periods of non-use during the day. Nonetheless, the most important implication of this savings is that enabling individual light control does have the tendency of saving significant amounts of energy while improving occupants’ satisfaction working under their preferred lighting. Daylight responsive systems have gradually gained popularity in modern buildings for saving up to 40% of electrical consumption (Jennings et al. 2000; Li et al. 2001; Tong et al. 2002). More and more affordable daylight responsive products have been on the market, encouraging their adoption in legacy buildings. Buildings equipped with daylighting
systems incorporating dimmable lights are prime candidates for adding this additional level of control for individual occupants. Not only can energy savings be increased, but occupants’ satisfaction in personalized lighting conditions leads to higher productivity. All of this can be done with minimal additional hardware cost. The objective of this paper, and the pilot implementation, is not trying to commercialize the system or the actuation modules, but to demonstrate a framework and the potential, feasibility, and acceptance of enabling individual lighting control in an operational setting. The entire implementation cost roughly $4,500 excluding development, software programming and labor time. Thus, it may be too early at this stage to discuss the payback time as most of the advanced energy efficient lighting systems can. All of the hardware components chosen in the implementation were well suited, yet not necessarily the best and the most efficient choices due to the availability and price of the small-quantity orders. There definitely is room for better selection of components, more compact packaging and design, and greatly reduced unit price once the system is ready for marketing. This system was implemented in an office without daylight, but savings on top of the 46% can be achieved once it is integrated with a daylight responsive system. This is the ongoing research for next implementation, and two methods to account for daylight are under investigation. One way is to integrate the system with a conventional daylight responsive system that has one photosensor mounted in the ceiling for each zone. The challenge here lies in the calibration of the photosensor, given that there is no single reference illuminance once individual control of the lights is enabled. The other method is to rely on desktop-mounted sensors adopting the same wireless sensor network technology as an extended research of (Granderson et al. 2004; Wen et al. 2004; Wen et al. 2006). We believe this is actually the right path for expanding the new lighting system. Given that a mote sensor will eventually be reduced to an unnoticeable size predicted by the tiny wireless platform researchers (Pister et al. 1999), it is affordable to redundantly deploy them on desktops or integrate them with decorations, PC monitors, etc. The sensed illuminance will be more close to the occupants’ lighting perception, and the local server of the system can easily incorporate the sensor information and automatically dim the lights to meet occupants’ preferences. Furthermore, the response model of the system during normal operation can be incorporated into the current watchdog function. This will enable the system to be self-diagnosing, and be able to track pending failures in any of the system components, notifying the appropriate party to initiate necessary maintenance before the fault occurs. It is well known that people have diverse and possibly conflicting preferences for lighting (Tregenza et al. 1974; Veitch et al. 2000). This poses a challenge when enabling individual overhead light control in shared-space offices. Leveraging the individually controllable lights, these conflicts could be better resolved as opposed to identically dimmed lighting in a zonal configuration. While the current system is equipped with the aforementioned simple algorithm, a more advanced algorithm looking into how to balance conflicting preferences under individually dimmable lighting is currently under development. This research formulates the task into an optimization problem that minimizes the total energy usage while constraining the light settings to meet each person’s preferences. This approach currently shows promising results and will be integrated into the new lighting system for verification.
ACKNOWLEDGEMENTS The authors would like to acknowledge the Chancellor's Advisory Committee on Sustainability (CACS) of University of California at Berkeley for partially funding this research. We acknowledge the PEC Tool Lending Library for kindly loaning us the ELITEproTM power meter. We thank Raul Abesamis, Elaine Ito, Medardo Largoza, and Sal Castro of the Physical Plant – Campus Service of UC Berkeley for supporting green energy projects and providing their retrofitting and consulting services for free. We also wish to thank Dr. Jessica Granderson for her advice, and Alireza Lahijanian for helping with the hardware assembly for the implementation.
REFERENCES Akyildiz IF, Kasimoglu IH. 2004. Wireless sensor and actor networks: Research challenges. Ad Hoc Networks 2(4): 351-367. Boyce PR, Veitch JA, Newsham GR, Jones CC, Heerwagen J, Myer M, Hunter CM. 2006. Occupant use of switching and dimming controls in offices. Lighting Research and Technology 38(4): 358-376. Crossbow Technology Inc. 2007. Product reference guide - end to end solutions for wireless sensor networks. Accessed 2008 March 10.
DiLouie C. 2003. Lighting and productivity: Missing link found? Accessed 2007 October 1. DiLouie C. 2004. Personal lighting control can increase worker satisfaction and motivation. Accessed 2008 March 7. Embrechts R, Bellegem CV. Increased energy savings by individual light control. In Proc Right Light 4. 1997. Copenhagen. p 179-182. Granderson J, Wen Y-J, Agogino AM, Goebel K. Towards demand-responsive intelligent lighting with wireless sensing and actuation. In Proc IESNA (Illuminating Engineering Society of North America) 2004 Annual Conference. 2004; Tampa, FL. Hakkarainen SP, MacAdam RL, Miller SC, Rowbottom I, Spira JS; Lutron Electronics Co., Inc., assignee. 1997 June 10. Remote control system for individual control of spaced lighting fixtures. US patent 5637964. Jennings JD, Rubinstein FM, DiBartolomeo D, Steven L B. 2000. Comparison of control options in private offices in an advanced lighting controls testbed. Journal of the Illuminating Engineering Society 29(2): 39-60. Kintner-Meyer MCW, Conant R. Opportunities of wireless sensors and controls for building operation. In Proc 2004 ACEEE Summer Study on Energy Efficiency in Buildings. 2004 August 22-27. Pacific Grove, CA. p 3.139-3.152. Lansing AT, MacAdam RL, Mayo N, Miller SC, Reiss RA, Rowbottom I, Spira JS; Lutron Electronics, Co., Inc., assignee. 2000 March 14. System for individual and remote control of spaced lighting fixtures. US patent 6037721. Levis P, Madden S, Polastre J, Szewczyk R, Whitehouse K, Woo A, Gay D, Hill J, Welsh M, Brewer E, Culler D. 2005. Tinyos: An operating system for sensor networks. In: Weber W, Rabaey JM, Aarts E, editors. Ambient intelligence. New York: Springer Berlin Heidelberg. p 115-148. Li DHW, Lam JC. 2001. Evaluation of lighting performance in office buildings with daylighting controls. Energy and Buildings 33(8): 793-803. Maniccia D, Rutledge B, Rea MS, Morrow W. Occupant use of manual lighting controls in private offices. In Proc Illuminating Engineering Society of North America 1998 Annual Conference. 1998. New York, NY. p 490-512. Mier-Langner A, Kuchar JE; Genlyte Thomas Group, LLC, assignee. 2002 April 11. Addressable system for light fixture modules. US patent 7027736. Mills E. 2002. Global lighting energy savings potential. Light and Engineering 10(4): 5-10. Moore T, Carter DJ, Slater A. 2002. A filed study of occupant controlled lighting in offices. Lighting Research and Technology 34(3): 191-205. Moore T, Carter DJ, Slater A. 2003. A qualitative study of occupant controlled office lighting. Lighting Research and Technology 35(4): 297-314. Moteiv Corporation. 2005. Tmote sky brochure. Accessed 2008 June 6. Moteiv Corporation. 2006. Tmote sky datasheet. Accessed 2007 November 13. Newsham GR, Aries MBC, Mancini S, Faye G. 2008. Individual control of electric lighting in a daylit space. Lighting Research and Technology 40(1): 25-41. Newsham GR, Veitch JA. 1998. Individual control over office lighting: Perceptions, choices and energy savings. Construction Technology Updates. O'Reilly F, Buckley J. Use of wireless sensor networks for fluorescent lighting control with daylight substitution. In Proc Workshop on Real-World Wireless Sensor Networks. 2005 June 20-21. Stockholm, Sweden.
Pister KSJ, Kahn JM, Boser BE. 1999. Smart dust: Wireless networks of millimeter-scale sensor nodes. Ranganath K, Kurnia A; MTI International, Inc., assignee. 1995 November 28. Distributed control system for lighting with intelligent electronic. US patent 5471119. Singhvi V, Krause A, Guestrin C, James H. Garrett, Jr., Matthews HS. Intelligent light control using sensor networks. In Proc 3rd international conference on Embedded networked sensor systems. 2005. San Diego, California, USA. ACM. Teasdale D, Rubinstein F, Watson DS, Purdy S. 2006. Final report: "Adapting wireless technology to lighting control and environmental sensing". The Interlaboratory Working Group. 2000. Scenarios for a clean energy future: Interlaboratory working group on energy-efficient and clean-energy technologies. Report nr NREL/TP-620-29379; ORNL/CON-476; LBNL-44029. Tong DW, Sing LK, Chung TM, Leung CS. 2002. Potential energy saving for a side-lit room using daylight-linked fluorescent lamp installations. Lighting Research and Technology 34(2): 121-132. Tregenza PR, Romaya SM, Dawe SP, Heap LJ, Tuck B. 1974. Consistency and variation in preferences for office lighting. Lighting Research and Technology 6(4): 205-211. Veitch JA, Newsham GR. 2000. Preferred luminous conditions in open-plan offices: Research and practice recommendations. International Journal of Lighting Research and Technology 32(4): 199-212. Wen Y-J, Agogino AM, Goebel K. Fuzzy validation and fusion for wireless sensor networks. In Proc ASME International Mechanical Engineering Congress. 2004; Anaheim, CA. Wen Y-J, Jessica G, Agogino AM. Towards embedded wireless-networked intelligent daylighting systems for commercial buildings. In Proc IEEE International Conference on Sensor Networks, Ubiquitous, and Trustworthy Computing. 2006; Taichung, Taiwan. IEEE Computer Society.
