8 LIGHTING CONTROLS 8.1 Overview

ADVANCED LIGHTING GUIDELINES 2003 EDITION 8. LIGHTING CONTROLS 8 LIGHTING CONTROLS Controls are an excellent way to reduce lighting energy while enhancing lighting quality. Occupancy sensors can eliminate wasted lighting in unoccupied spaces. Daylighting controls or advanced load management can reduce lighting demand when energy is most expensive. And manual dimmers, which allow occupants to adjust light levels to their preference, are becoming more affordable. Lighting controls have been shown to reduce lighting energy consumption by 50% in existing buildings and by at least 35% in new construction. More discussion of potential savings is provided later in this chapter. In the past, the common light switch was the primary means of controlling lighting in buildings. However, specifiers are starting to implement more advanced controls due to a reduction in the cost of control hardware and other technological developments. This is resulting in very significant energy savings while offering occupants something in return—better control of their lighted environment. Today, lighting controls are entering a new era, where they will be considered not just for saving lighting energy but as a real amenity for the people for whom buildings are built. This chapter is organized into six sections. The first section (8.1) addresses user and energy-saving issues related to controls. The next five sections deal with specific control technologies: switches and dimmers (8.2), occupancy sensors (8.3), daylighting controls (8.4), building-level controls (8.5) and other controls strategies (8.6). 8.1 Overview The positive benefits of controls depend on both the occupants and building managers understanding how the lighting systems and controls work. This section describes lighting control issues that specifiers must be knowledgeable about if controls are to be used as intended. 8.1.1 Occupant Needs Lighting controls are intended to fulfill two, potentially conflicting, objectives: (1) reduce lighting energy costs and (2) maintain or improve occupant satisfaction and comfort. Except for the most humble of lighting controls—the manual wall switch—lighting controls have historically had little to offer the building occupants. In the past, the occupants' lighting control needs were thought to be adequately served if they could turn their lighting on or off when arriving or leaving work. In the modern work environment, this attitude is no longer sufficient. Changing visual needs are now the norm rather than the exception and controls can help to meet this variety of needs. For example: • With the widespread use of computers in the workplace, lighting needs and preferences may change from hour to hour and from day to day. Mixed tasks may require different lighting conditions. If occupants have the ability to easily change lighting conditions according to task or even mood, lighting controls can add to occupant comfort and satisfaction. (See section 4.3 for more about design considerations to meet changing visual needs.) • Modern office workers move around more, since they do not stay in one job as long as they used to and also because workplaces are rearranged more frequently. A flexibly controlled lighting system can accommodate a high relocation or "churn rate." (Refer to section 4.3.2 for further discussion of workplace flexibility needs.) • A new development in the workplace is the concept of "hot-desking" or “hoteling” where one workstation may serve a number of different people from day to day and week to week. Again, this requires a flexible lighting system that can provide different light levels for different tasks and workers’ needs. This is described in more detail in section 4.3.2. 8-1 ADVANCED LIGHTING GUIDELINES 2003 EDITION 8. LIGHTING CONTROLS • Furthermore, as the median age of workers increases, an increasingly large proportion of older workers may want and need higher levels of illumination. Although sensitivity to glare also increases with age, older workers generally need more light, especially for viewing paper tasks with small type. (The effects of aging on vision are discussed in section 2.1.6; design strategies to reduce glare are provided in section 4.3.2.) While building managers are used to paying attention to the thermal comfort of workers, paying attention to visual comfort is somewhat new. Since the human visual system is so adaptable, workers are less likely to complain about lighting. However, good lighting contributes to overall interior environmental quality, and many employers are realizing that a better environment leads to many benefits, including helping them retain employees. Most people don’t think about lighting or lighting controls unless the lighting is so bad that they can’t perform their work. To be acceptable to building occupants, automatic controls must not disrupt normal working activities. A user must be able to control his or her lighting without affecting others. Users should be able to adapt their lighting according to personal preference and need. The use of lighting controls should be intuitive and obvious. While most users will not notice a 15–25% gradual change in illumination, abrupt changes in light level are distracting and should be avoided, especially for occupants performing stationary tasks. 8.1.2 Building Operation Cognizant building managers use the building lighting control system as a tool to control building operation costs. Since lighting energy is a substantial fraction of electric energy in many buildings, improved lighting controls can have a major positive impact on building energy consumption and peak demand. Savings from lighting controls may come from: • Reduced electric lighting use • Reduced peak demand charges • Downsizing HVAC equipment (reduced first cost) • Reduced HVAC operating costs • Lower maintenance costs • Productivity improvements Lighting also affects other building loads, especially HVAC. The usual “rule of thumb” is that every watt saved in lighting saves an additional 1/4 watt in avoided HVAC energy (see also section 4.4.3 – Economic Analysis of Lighting Systems). Lighting controls must be compatible with existing lighting equipment (luminaires, lamps, ballasts and wiring) and not cause premature equipment failure. Since lighting controls components are usually obtained from multiple vendors, the specifier must be knowledgeable about the interactions between lighting controls and lighting equipment. Sometimes these interactions are surprising—for example, specifying the wrong type of ballast may cause premature failure of lighting contact relays. (Chapter 6 discusses light sources and ballasts; chapter 7 discusses luminaires.) Controls must be reliable and work correctly virtually all the time. An occupancy sensor that misbehaves even once a week (by turning off lights in an occupied room, for example) may be disabled by a disgruntled occupant. A daylight sensor that dims lights too much as clouds move past will be distracting, causing occupant complaints, and may be disabled. Most controls require commissioning to ensure that they operate according to design intent and are properly adapted to local conditions. With occupancy sensors, the time delay and sensitivity should be adjusted for each workspace; for example, the sensitivity should be set higher in spaces with little occupant movement (such as offices where keyboard entry is the main task). With automatic daylighting controls, the sensitivity to changes in daylight must be set for local room conditions. Initial commissioning may be done by a professional or by the facility management staff, but for best 8-2 ADVANCED LIGHTING GUIDELINES 2003 EDITION 8. LIGHTING CONTROLS performance, occupants should be involved in fine-tuning control system operation according to their preference. Since furniture, occupants and activities often change, lighting controls must be flexible and reconfigurable. If a lighting control is hard to adjust or requires frequent “programming” it will probably not be used effectively. Adjustments and tuning of lighting controls should be accessible and understandable to personnel authorized to make such adjustments. Sensors should not require undue maintenance or drift significantly. Access to photosensors for cleaning should be considered in the specification and design of the system. Controls that have visible indicators or annunciators are useful to informing building personnel as to whether equipment is functioning properly. 8.1.3 Control Selection Guidelines This section provides an overview of general control strategies and devices, as well as several useful tables to evaluate which strategies and devices are appropriate for various space types. For a more detailed discussion of specific control strategies and devices, see sections 8.2 through 8.6. Control Strategies There are several general strategies for using lighting controls to reduce operating costs and improve lighting system functionality: 1. Occupancy Sensing: Turning lights on and off according to occupancy as detected with occupancy sensors. Appropriate for unpredictable occupancy patterns. Section 8.3 covers occupancy sensing in detail. 2. Scheduling: Turning lights off according to program using programmable relays, timers and other time clock devices. Appropriate for predictable occupancy patterns. Advanced scheduling strategies are discussed in section 8.5.2. 3. Tuning: Reducing power to electric lights in accordance with the user needs at the time. Tuning may be accomplished with dimming devices, but bilevel

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