Your questions answered: Designing a holistic lighting system
Codes, standards and research require lighting engineers to consider daylighting, high-quality lighting products, controls and commissioning in lighting designs to achieve a holistic design that meets the needs of the building occupants. Requirements for lighting become more complex with each edition of the energy conservation codes.
Codes and standards include ASHRAE Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings, the International Energy Conservation Code and California Title 24.
During the Aug. 8, 2019, webcast Lighting: Designing a holistic lighting system, some questions were left unanswered. Several of them are answered here.
- Sara Lappano, PE, LEED AP, Integral Group
- Sara Schonour, LC, Assoc. IALD, CannonDesign
Question: Can you please talk a little about integrating daylighting into electric lighting?
Sara Lappano: Designing photosensor dimming controls to work with the daylight distribution in a space is critical to achieving energy savings through daylighting. Also, keep in mind that the electric lighting must be effective on its on during times when sufficient daylight is not present for most applications.
Question: Is there any specific code or standard for stairwell lighting in high-rise buildings?
Sara Lappano: Yes, the energy codes reviewed during the webcast all have requirements for stairwell lighting, both in terms of allowable wattage as well as controls. They differ by code, so you should check the specific code that applies to your project (some require partial dimming on stairwell lighting when no occupants are present).
Question: Our team is having problems finding commissioning agents to certify projects. Do you have any recommendations?
Sara Lappano: ASHRAE offers a certification that commissioning professionals can get — BCxP (building commissioning professional certification). The ASHRAE website has directories of professionals with this certification.
Question: What’s a good rule of thumb for the maximum number of lumens for a 2– x 4-foot light fixture?
Sara Schonour: A good rule of thumb is 10,000 lumens for typical one-story ceiling heights (8 to 12 feet).
Question: How do you balance holistic design against tight budgets/value engineering exercises?
Sara Schonour: Our best strategy to achieve our design and protect our specifications from value engineering is to get lighting into the conversation early and educate the owner about the value of the lighting products/systems in the design. Data are often our best friend in these conversations — another reason we need more lighting research!
Question: Does contrast ratio take into account the fixture aperture size? Do two 1,000–lumen fixtures that are different sizes have a 1:1 ratio?
Sara Schonour: Contrast ratio is not about the brightness of the aperture — that’s more related to glare. Contrast ratio is the ratio (or relationship) between the light falling on a task or display and the general lighting in the area immediately surrounding it.
Question: How do you adjust your design to accommodate for daylight? How does daylight affect how you design different lighting layers?
Sara Schonour: Today’s tools for daylight analysis allow us to predict how much daylight will be available in a specific place at a specific time and we can harness that information to reduce electric lighting via control systems. In a best-case scenario, manipulating daylight is also possible by coordinating with the architecture and design team to optimize architectural forms, plan for potential glare and capture the positive energy benefits daylight allows — before the electric lighting system is even designed.
Question: Is there a standardized or preferable way to display code compliance and extra considerations regarding lighting in a floor plan?
Sara Lappano: Demonstrating energy code compliance in terms of lighting power density is typically done in table format rather than on plans because the reviewing authority may want to see the assumptions and math behind demonstrating compliance with watts/square foot limitations. Also, some jurisdictions require documentation through the U.S. Department of Energy’s COMcheck be included in drawings, which is a free tool that allows design teams to input building design characteristics (envelope and building systems) and then receive an output documenting whether the design is compliance with the applicable code.
Question: Which lighting code is the most efficient to comply with? California Title 24, International Energy Conservation Code or ASHRAE Standard 90.1?
Sara Lappano: The first question should be: “Which energy code is required for the jurisdiction where the project is located?” Then, if multiple options are available, the entire design team needs to discuss and decide on which code makes the most sense for the project. Each code has different requirements and they vary by which year the code was issued. No one code is really more energy–efficient or easier to comply with.
Question: As a younger engineer who has not seen much of his or her designs from AGi32 or ElumTools actually constructed, how different are the results from the model versus what is measured in the field?
Sara Schonour: AGi32 and ElumTools are accurate in some ways, but not all. There are many variables inputted into the virtual environment (light loss factor is just one example) that will affect the output, so the old “garbage in, garbage out” adage applies. To dial down on accuracy, it’s important to tune each of those variables.
Question: What are the lighting code requirements for water and wastewater treatment plants?
Sara Lappano: The answer to this varies, since different jurisdictions adopt different energy codes. The authority having jurisdiction is ultimately the party that mandates which energy code should be followed for these types of facilities. Most of the energy codes do have some allowances and exceptions for industrial applications or scenarios where lighting is critical to the safety of occupants and personnel.
Question: During the fluorescent demonstration, the temperature averaged 3,500 Kelvin. In the LED lights, I saw 4,000 Kelvin. Is this correct?
Sara Schonour: Correlated color temperature is a design choice, highly dependent on the application and the material palate, and there is no hard and fast “right answer” for color temperature preference. In general terms, we typically see warmer CCTs (2,700 to 3,000 Kelvin) in residential applications, 3,000 to 4,000 Kelvin in education/corporate environments and 3,500 to 4, 000 Kelvin in most health care/science and technology applications.
Question: How does return on investment play into the process of designing lighting systems?
Sara Schonour: ROI can play a big part in justifying the first cost of LEDs, particularly when comparing to a legacy technology like fluorescent or incandescent, where the energy and maintenance benefits are clear. As research becomes more available, other metrics to measure ROI are emerging, related to patient release times in hospitals, increases in productivity, etc.
Question: What does an LED driver do?
Sara Schonour: The driver plays a similar role to a ballast in a fluorescent system. They do two jobs: They handle the higher voltage, alternating current to the low–voltage, direct current that LEDs typically run on, and they also protect LEDs from voltage or current fluctuations.
Question: What tool(s) do you use to calculate and track lighting power desity when using the space-by-space method of energy code compliance?
Sara Lappano: With the use of building information modeling, the calculation of allowable LPD using the space-by-space method is getting easier and less time–consuming. It is possible in some of these programs to assign ASHRAE space types to each room in the building, which can then be used to calculate the allowable LPD using the space by space method. Without BIM, this calculation is more of a manual effort, which is what we demonstrated in the webcast.
Question: What is your opinion on harmful blue light on humans and need to stay at 3,500 Kelvin for human well-being as opposed to just tossing in 5,000 K lighting?
Sara Schonour: The research on this topic is still emerging. In some cases, blue light can be helpful; in others, harmful. We need more concrete study on the subject before we can make sweeping decisions related to light and color and its effect on our bodies.
Question: What particular study or fact do you feel demonstrates the value of a holistic design?
Sara Schonour: A good example is a recent study from Sacramento Municipal Utility District that looks at the power of routine and the effect of light and color when used in populations that require strict routines to function. By considering not just the quality, color and type of light but also the timing and duration in the environment and the habits and needs of the individual, we’re really pushing the boundaries of traditional lighting design into a more holistic paradigm.
Question: How does the code affect space to mounting–height ratios?
Sara Lappano: Space–to–mounting height ratios are spacing guidelines provided by light fixture manufacturers to help design teams ensure lighting at the floor of a space is fairly even. These are not code requirements but are important to the “quality” of the lighting in a space. The energy code is generally focused on how much energy the lighting is using, not whether the lighting is even in a space. The energy code takes precedence over any manufacturer recommendations. In my experience, the design of lighting is a balancing act between providing a quality environment for occupants while also ensuring that the energy code is complied with. Lighting calculation software is frequently used to ensure both of these considerations are being met.
Question: If emergency lighting fixtures also being used for general illumination in the space, do these fixtures need to be used in LPD calculations?
Sara Lappano: Yes, emergency lighting that is normally on and is used for general illumination needs to be included in LPD calculations. Exit signs are not included in this, but the energy codes have requirements for how much power these signs are allowed to consume.