Lighting efficiency – More than LEDs alone
As we become more energy efficient, lighting design is a great place to start in the built environment
- Know the three steps lighting design should always involve.
- Learn the importance for each role on a project team to understand lighting controls for a design.
- Understand the difference between task-ambient lighting design approach and a lighting controls design approach and which scenarios each would be applied.
Lighting Efficiency Insights
- Energy efficiency can be achieved in lighting design by paying attention to a few key factors.
- Lighting controls can reduce energy use by ensuring lights are turned on and off at specific times, or by reducing ambient light when daylighting can illuminate a space.
LED technology has increased efficacy of luminaires resulting in less energy being used to light buildings, however it is not enough to assume that simply using LED technology means that you are producing energy efficient and code compliant designs. Recent code updates have dramatically reduced the permitted connected lighting loads in response to improved equipment capabilities. Between 2016 and 2019, ASHRAE Standard 90.1, energy standard for sites and buildings except low-rise residential buildings, reduced permitted lighting power densities between 14% and 25%, the largest decrease since fluorescent technology replaced incandescent. Lighting efficiency is about more than using LED technology and calculating lighting power density. To embrace our quest for net zero and to reduce our energy footprint, we need to provide lighting designs that are both thoughtful and intentional. Lighting design should always involve three steps:
- Understand task and ambient illumination needs, as well as meeting any codes and standards that apply
- Specify lighting controls that work with the luminaires and with the occupants.
- Specify lighting equipment that is suitable for the environment and can be easily maintained or recycled.
The first fundamental approach to providing lighting efficient designs is using a task-ambient design approach. Task-ambient design starts by identifying what tasks will be performed, and if those tasks are limited to select areas of a room or occur throughout the room. Often, high-performance tasks that require higher illumination levels are contained to an area that is smaller than the entire room. Instead of illuminating the entire room to the higher illumination level needed for one task, energy can be saved if the higher illumination need is applied only to task performance areas.
Task-ambient designs can also be achieved using nonuniform fixture selections and placements, or through smaller dimmable control zones. Gone are the days of continuous arrays of recessed troffers applied throughout all spaces. Perhaps, the most easily identified example of task-ambient design is seen in laboratories. Laboratory workbenches and shelving require higher and more uniform illumination than corridors and aisleways; often having fixed locations with sinks, gas accessibility and utility connections. Laboratory workbenches typically have luminaires located over the edge to mitigate shadows. This lighting layout that produces 80-100 footcandles at 36 inches above finished floor on the benchtop, will typically produce 10-30 fc in the aisleways without the need for any additional fixtures in the aisles.
Even though these are generally sold as flexible work environments, task-ambient designs should also be used in open office spaces, with desktops spread uniformly through a space. The lighting is often much more uniform, yet like laboratories, these office spaces will sometimes have defined circulation zones, in which the same design approach may be taken. There is also a second layer to the task-ambient approach that is generally applied to open office lighting. This approach provides supplemental task lighting to give the occupant the ability to increase illumination for task specific needs, that are not the dominant task conducted. The majority of office tasks today are computer based, which has lowered the recommended illumination level from 50 fc at 30 inches aff to 30 fc at 30 inches aff. This does not mean that paper-based tasks no longer occur; however, the illumination needs for paper-based tasks are more limited, sporadic and best addressed through task lights that can be individually controlled as needed.
This also means that these fixtures should not be occupancy sensor controlled, turning on simply because someone is sitting in their chair. The best way to control these task lights are via dimmable vacancy sensors. The person who needs additional illumination must manually turn the light on and is able to adjust to their specific need. However, if they forget to turn off and leave their desk area, the light will automatically turn off. It is important to note that several European standards still require offices to be illuminated with 500 lux; if you are designing to these standards, there is no need for supplemental task lighting.
Understanding the recommended illumination needs for each space is fundamental to providing not only functional, yet energy efficient lighting layouts. Investigate if there are any corporate standards or industry standards related to lighting that must be followed. The Illuminating Engineering Society offers many recommended practices for specialty building types and provides guidance for common applications and exteriors. In these American National Standards Institute approved documents produced by the IES, the illumination tables provide recommendations for both rooms and tasks. When reviewing, be sure to take your time and read the tables – including footnotes. Understand how building occupants plan to utilize the rooms. Is the equipment fixed or is it flexible? Lighting designs tailored to space utilization and visual performance needs will not only conserve energy, this approach will also enhance occupant comfort. Quality lighting must balance brightness and uniformity within visual task areas to avoid an environment that causes eyestrain and fatigue (see Figure 2).
Taking time to understand space utilization within the built environment is instrumental for the second energy conservation design approach – lighting controls. Lighting controls offer the largest opportunity for energy savings. Lighting controls are also the most difficult and overlooked aspect of lighting construction documentation. Due to the plethora of driver types, control protocols, proprietary addressable systems and lack of standardized componentry with LED technology and the associated control devices and systems, it is next to impossible to document a fully detailed control riser, device placement and competitive bid specification identifying all apparatuses.
If you rely on manufacturers or manufacturer reps to prepare your control specifications and wiring diagrams, you should realize that you are providing a proprietary bid package. The most effective method to offer a competitive bid package is to provide a performance specification. This requires clear communication of all critical components and how the system is to function. Remember to coordinate and communicate any interconnections with other building systems, such as the mechanical building automation system and audio-visual systems. This involves differentiating between primary triggers and overrides, which cannot be achieved simply by showing control devices on a plan. The most effective way to communicate performance is through schedules and verbiage – a written sequence of operation for each control zone.
For instance, “occupancy sensor turns lights on and off; daylight harvesting photocell overrides intensity maintaining 30 fc on desktops.” The way each and every luminaire is controlled is integral to a lighting design, and every professional lighting designer should develop a documentation system that clearly communicates how each luminaire is controlled. Lighting controls must be understood by multiple project team members, not just the electrical contractor who needs to install them.
Lighting controls should be presented alongside lighting designs for client buy-in. This is often the best time to seek client feedback for how they intend to utilize the space. If the end user does not understand how the system is designed to work and what adjustability it has; the system will not be fully utilized at its optimum.
2. Electrical engineers
The electrical engineer will need to understand the lighting controls to assure the circuiting is aligned with the control zones and how the emergency lights are controlled. If the lighting designer specifies control zones, these are groupings of luminaires that all act together. One zone may be comprised of one or more relay. One circuit may feed multiple relays, yet one relay cannot be fed from multiple circuits. When emergency lights are controlled, there are typically two methods that can be used and must always be UL924 compliant. One method control uses a UL924 compliant transfer device that switches the luminaire from a normal circuit to an emergency circuit. Another type of UL924 compliant switching device senses the unswitched normal circuit, and when this transmits down the control signals are bypassed leaving the emergency circuit on.
3. Control manufacturer/reps
The vendor must understand the desired performance of the lighting control system, the approved luminaire driver types, and the reflected ceiling plans in order to provide accurate pricing and shop drawings. Field programmable systems often include a field technician who travels to the job site to program and startup the system. This technician is often not the person who curates the shop drawing submittals; however, the technician will be relying on the shop drawings during field startup. Therefore, it is important that the sequence of operation provided in bid documents is reiterated and thoroughly examined during the shop drawing submittal and review process.
4. Commissioning agents
The commissioning agent will need to understand how the system is meant to perform under all conditions. This understanding allows them to establish proper testing methods to assure the system is functioning as designed before owner occupancy and training.
Understanding and respecting the important role that each member plays in the process helps guide the production of clear and concise constructions documentation.
Understanding luminaire construction is also important when balancing luminaire efficacy and performance. For instance, a luminaire without a lens will produce more delivered lumens per watt than a luminaire without a lens. That does not mean that luminaires without lenses should be used. LED modules are very bright point sources that are not comfortable for direct viewing. If you need to close your eyes to be comfortable, it does not matter how much more efficient the luminaire is – it is not working effectively. An indirect fixture used where no occupant will have a direct view may not need a lens to prevent glare yet may require a lens in order to create a batwing distribution for more even illumination with fewer fixtures. This also does not mean that only fixtures with lenses should be used. There are other ways to conceal direct views and improve photometric distribution through housing, reflectors and even the LED array design.
As we look to increase lighting efficiency and decrease our carbon footprint, it is also important to keep life cycle efficiency in mind. Can the driver and LED arrays be field replaced, or is a whole new fixture needed when it reaches end of life? LEDs do not last forever. They will produce less light over time and need to be replaced. The published life for LED performance luminaires is when these are expected to dim to 70% of their initial delivered lumens, while the published life for LED decorative luminaires is when these are expected to dim to 50% of their initial delivered lumens. Lighting maintenance impacts our carbon footprint, making this important to specify luminaires that are suitable for the environments the products are placed within. Temperature extremes, water, vibration and impacts can all shorten the expected life of luminaires that are not designed for these conditions. It will not matter if the luminaire has field serviceable LEDs and drivers if the luminaire, itself, does not last long enough to be serviced. Reducing facility maintenance makes for happy clients and a happy planet.