Lighting insights:

• A lot of information about codes and standards, specifically ASHRAE 90.1, is touched on as it relates to energy-efficient lighting systems.
• What’s the difference between CRI and CCT?

During this Aug. 25, 2022, webcast on “Lighting and lighting control design,” many questions remained. Here are several answers from the experts.

Lighting designers must consider many factors when specifying lighting systems and lighting controls for nonresidential buildings, including the owner’s project requirements. Elements that designers must be aware of that will be touched on are:

• Lighting construction budget.
• Code requirements.
• Desired light source, color temperature, color rendering index, etc.
• Desired luminaire type and style.
• Illumination levels, minimum foot-candle levels, maximum foot-candle levels, maximum to minimum foot-candle ratios, etc.
• Desired controls systems.
• Special requirements such as emergency lighting, daylighting harvesting, dark skies, etc.
• Sustainability goals.
• Commissioning requirements.
• Training requirements.
• Operations and maintenance requirements.

Presenters:

• Michael Chow, PE, CEM, CxA, LEED AP BD+C, principal, Metro CD Engineering LLC, Columbus, Ohio
• Tony Staub, PE, LC, lighting design lead/electrical project engineer, Specialized Engineering Solutions, Omaha, Nebraska

What’s the best way to apply “lessons learned” after completing a design you will never see in day-to-day use, and without knowing what the shortcomings of the design are?

Michael Chow: Functional testing/commissioning is required by ASHRAE Standard 90.1: Energy Standard for Buildings Except Low-Rise Residential Buildings. The lighting designer or electrical engineer should work with the commissioning agent to implement the functional testing forms and requirements. The completed forms could be reviewed with the lighting designer or electrical engineer.

Also, the lighting designer or electrical engineer can require post-occupancy testing. This is required for the optional U.S. Green Building Council LEED Enhanced Commissioning credit.

LEED requires that lighting be separately metered. The lighting designer or electrical engineer can use this data and compare it to the energy model or anticipated lighting usage to determine if the actual data matches the design data. If not, perhaps the lighting controls need to be revalidated or re-commissioned.

How do you specify a lighting control system while keeping the spec open to multiple manufacturers?

Tony Staub: Using a performance-based specification including a detailed sequence of operations is my method. By defining what the system must be capable of, you can meet the needs of the project without selecting one system.

Can you please elaborate more on “daylight harvesting”?

Tony Staub: Daylight harvesting is simply reducing artificial lighting levels (and associated energy) while sufficient daylight is available within a space.

Other than saying the code requires it, how do you sell a client on a controls system who only wants toggle switches on the wall and doesn’t want a complicated system? And by that, I mean code minimum dimming, daylight controls and sensors.

Tony Staub: This is highly dependent on the client and the application of the building.

What standards say about the warranty period and battery backup (in hours) of essential lightings fixtures?

Michael Chow: Standards usually do not address the warranty period. NFPA 101: Life Safety Code Section 7.9 requires emergency lighting must remain illuminated for at least 90 minutes. Illumination levels are allowed to decline to an average of 0.6 foot candles (fc), with a 0.06-fc minimum, at the end of the 90-minute period. It is critical that the lighting designer or electrical engineer consult with the code official before during the design phase. Code officials may interpret the required illumination levels differently and may lead to increased construction costs and delays if the code official interpretation is not determined during the design phase.

Color rendering index (CRI) gives higher level of color rendering?

Tony Staub: Theoretically, though CRI is limited in application. CRI is developed using eight reference colors and includes no metric for saturation. In short, a higher CRI should provide better color rendering on average, though that may not be true for specific colors. TM-30 provides additional information, which can be used to better understand the color qualities of a light source.

How does CRI compare to color temperature?

Tony Staub: CRI and correlated color temperature (CCT) are measures of different things, though there is some relationship. CRI compares how light sources render a set of colors as compared to a reference point. Changing CCT would change those reference points slightly, but CRI would still apply in the same way. In short, there is very little relationship between the two.

Isn’t “auto on” a non-energy-conserving spec?

Michael Chow: Occupancy sensors automatically turns on the lights when it detects the presence of a person in its field of detection (usually a major and a minor field) and turns the lights off when no one is present. A feature of occupancy sensors is that they automatically turn on and turn off when occupancy is detected in either the major or minor sensor coverage areas. It can be programmed to turn on or off only part of the lights during occupancy — some of this is code required. This strategy is also called partial ON/partial OFF control.

A vacancy sensor can be more energy efficient compared to occupancy sensors. Vacancy sensors will keep the lights off in a room/area unless they are activated manually with a vacancy sensor. This can also be advantageous as a room occupant may not always want artificial lighting. This allows the occupant to control if artificial lighting is present or not. Vacancy sensors turn the lights off when no one is present. This strategy is known as manual ON control.

You talked about CRI, but any thoughts on TM-30 or just CRI+R9?

Tony Staub: I personally believe and hope that TM-30 will continue to gain popularity, as I believe there are a number of TM-30 metrics which could be used in lieu of CRI for more impact.

If ASHRAE 90.1 can be used in lieu of International Energy Conservation Code, does it matter how far back the latest adopted version is?

Michael Chow: IECC for jurisdictions that have adopted the IECC. Use the ASHRAE 90.1 version issued two years before IECC version. However, check with the state and local lighting codes as they may have adopted another version of ASHRAE 90.1 as acceptable.

Can mechanical systems use different energy code from the electrical energy code?

Tony Staub: No. The same energy code must be used by the entire design team, including not only the mechanical team but also the architectural team. In fact, there are some code provisions that require the participation of multiple disciplines, such as the “Additional Efficiency Package Options” in the IECC 2018.

Can ultraviolet (UV) lighting be used in retail settings?

Tony Staub: A good UV design can be used in most space types. For a retail space with daily hours, a system set up to provide pulsed UV to disinfect overnight may be a good solution.

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