CRI Modulation: Future Lighting Control Strategy?

CRI Modulation

Craig DiLouie

LED lighting has made a new dimension of lighting control, colour tuning, widely available. By mixing separately dimmable arrays of warm- and cool-white, saturated colours (RGB+A), or a mix of the two, correlated colour temperature (CCT) can be tuned manually or automatically based on various application needs.
Besides CCT, the source’s colour rendering index (CRI) can be raised or lowered within a given range. The maximum depends on the source, while the minimum depends on the designated CCT. This is accomplished by gradually reducing the red component of a red, blue, green and either yellow or amber mix.

While the primary benefit of modulating CCT is aesthetics, the primary benefit of modulating CRI is energy savings. As CRI declines, luminous efficacy increases. This creates a potential energy savings opportunity in spaces that must remain illuminated at full output and constant CCT while unoccupied.

David L. Bay, LC, corporate engineer for Osram Sylvania, sees airport concourses as a potential application for this novel control strategy. The lights must remain on and at full output at night for safety, though for much of the night large parts of the concourse may be unoccupied. CCT must be maintained because changing CCT would be objectionable from an aesthetic point of view.

In this application, the lighting in the main circulation spaces would be zoned to operate at full output and specified CCT and CRI. Lighting in peripheral areas would be separately zoned, with CRI reduced based on occupancy or a schedule.

“CRI modulation would be suitable for applications with certain characteristics,” Bay says. “Notably, applications where maintaining high lux levels for safety or other reasons is important, and where the space is granularly occupied at different times of the day.”

Actual energy savings would depend on the application, though Bay believes at least 10% would be typical, and up to 25+% has been demonstrated. Another question is whether occupants would find a change in CRI objectionable.

In 2005, the Massachusetts Institute of Technology (MIT) conducted a study in an open office and two private office spaces at the institute’s Media Lab. The researchers wanted to know how far CRI could be reduced before occupants noticed the change and/or found it objectionable.

Eight OSRAM SYLVANIA LED panels were installed in the ceiling of the open office and two each in the private offices. These LED panels were colour tunable and of an experimental design. CCT was maintained at 5000K, light levels at about 30 footcandles. The study participants —13 graduate students with no prior knowledge of the study — were asked to perform tasks in the spaces. While they were working, CRI was adjusted over a period of three seconds from 89 to 68. Shortly afterwards, a pop-up questionnaire appeared on their screen asking what activity they were doing and whether they noticed the change.

Three hundred and twenty of these queries received responses; of these, 203 responses (63%) indicated a change had not been noticed. Changes were more likely to be noticed when occurring in the immediate area or simultaneously in the immediate and peripheral areas. Changes were least likely to be noticed when they occurred solely in a peripheral area.

“Experience suggests CRI modulation within an occupied space will not be well accepted,” Bay notes. “The concept of CRI dimming is currently founded on modulating CRI of unoccupied spaces adjacent to occupied spaces.”

CRI modulation was considered a good potential if not practical strategy at the time of the study. LED technology has made significant advances since then, making it practical. Still, Bay notes, the requirements of colour-mixing LEDs and granular zoning pose a cost that challenges economic viability. As LED technology continues to progress, however, CRI modulation may become viable from an economic as well as a technological standpoint.

Bay sees CRI modulation being paired with another potential control strategy, which is using LED general lighting as an indicator. For example, peripheral lighting in a private office could automatically adjust to become red when the occupant is on the phone, both saving energy while indicating the occupant should not be disturbed. This potential has many applications.

“Colour tuning has opened a vast potential in lighting design and application, and we are just beginning to pioneer,” Bay says. “While these applications focus on aesthetics with some interest in circadian health, this extraordinary emerging dimension of lighting control may also be used to maximize energy savings.”

Craig DiLouie, LC is acting education director for the Lighting Controls Association.

This article was reprinted with permission of the Lighting Controls Association,



Related Articles

Changing Scene

  • Magic Lite & EFC Release Student Scholarship

    January 18, 2023 Magic Lite was thrilled to have participated in the 2022 EFC Scholarship Program and recently present the Magic Lite Future Leaders Award of $2,500 to Anthony Faustin of Sherbrook University in Montreal. As successful applicant, Anthony demonstrated leadership amongst his peers as well as in his community, and showed true entrepreneurial spirit… Read More…

  • Ascot Capital Group Announces a Change in the Presidency and the Appointment of Rob Nadler as President

    January 18, 2023 Rob Nadler, Stanpro’s Executive Vice-President will be promoted and assume the role of President of Ascot’s “General & Emergency Lighting Group – Stanpro, AimLite & Beluce” effective June 1, 2023. Rob joined Stanpro in 2001 and was instrumental in its tremendous growth over the past 20 years, including the organic acceleration of the business, the… Read More…


  • LIT Design Awards Light Art Project Winner: Integral Group

    LIT Design Awards Light Art Project Winner: Integral Group

    December 19, 2022 Prize(s) Winners in Light Art Project Company Integral Group Lead Designers Ellie Niakan + Catherine Chan Photo Credits Catherine Chan Completion Date December 21, 2021 Project Location New Westminster, British Columbia, Canada Although appearing as solitary, trees are connected to one another through vast underground systems known as mycorrhizal networks. Through these hidden systems—a symbiotic relationship between plants… Read More…

  • LIT Lighting Design Awards: Capital Park Landscape, Victoria, BC

    LIT Lighting Design Awards: Capital Park Landscape, Victoria, BC

    December 5, 2022 Located in one of Victoria’s most historic neighborhoods, the Capital Park Mixed-Use Development is made up of seven buildings stretching across three lots and is responsible for nearly an entire city block of Victoria’s downtown core. The project took place over the span of three phases and eight years. The first phase… Read More…

New Products

  • JSBT Tapered Switchable White Surface Mount Disk Light

    JSBT Tapered Switchable White Surface Mount Disk Light

    January 27, 2023 JSBT SlimBasics™ Tapered LED Disk Light Series comes in 4″ and 6″ sizes and provides even illumination where you need it most. Designed to provide good lighting quality, while also being budget friendly, the JSBT is the lowest total install cost LED solution for residential spaces. The matte white aluminum housing is… Read More…

  • 2″ Purist™ luminaires

    January 27, 2023 Meticulously designed, Purist was created with versatile light, beam, adjustability, and finish options that allow you to illuminate your environment in your light. 2″ Apertures (1.25″ with Pinhole trims). Up to 1500 lumens per lamp. 25° Vertical tilt. 2700K-4000K Color temperatures. 3000K-1800K Warm dimming. 15°-65° Beam Spreads. Wall Wash Available. For more… Read More…