A custom-mixed LED spectrum rated at just 80 CRI helped people in their 70s and 80s sort colors more accurately than a daylight reference rated 97, according to a study published Oct. 13 in Optics Express. The result does not mean the lower score was an advantage in itself. The spectrum was tuned for aging eyes, the researchers say.
The research, from Fudan University in Shanghai with two Opple Lighting employees among its eight authors, starts from a familiar problem. As the eye's lens yellows with age, it filters out short-wavelength light. Ra and TM-30, the color metrics specifiers use, are calculated with a fixed standard observer that makes no allowance for lens aging, even though the CIE's own 2006 physiological model includes an age parameter.
Modeling aging eyes
The team modeled the color response of aging eyes and created two metrics. One estimates how much lost color discrimination a spectrum recovers for an older viewer; the other measures color fidelity against a 32-year-old's perception. They screened 11,541 candidate spectra from a 16-channel LED luminaire, all at 5000 K with Ra of at least 80.
Two candidates were tested against a simulated D50 daylight reference with Ra of 97. P1 prioritized discrimination at Ra 80. P2 balanced discrimination and fidelity at Ra 90. When the authors re-ranked every candidate using the conventional standard observer, P1 lost its top position. The spec-sheet favorite and the aging eye's favorite can be different lights.
Color-sorting results
Participants aged 70 and older, with a mean age of 81.7, sorted colored caps from the Farnsworth-Munsell 100 Hue test in a viewing booth at 300 lux. Mean error scores fell from 79.2 under the reference to 62.4 under P1 and 65.0 under P2, and both drops were statistically significant. Color discrimination improved for 26 of 34 participants, or 76.5%, under P1 and 22 of 34, or 64.7%, under P2. The gap between the two optimized spectra was not significant.
Asked whether fruits and vegetables looked natural, 28 participants said yes under P1, compared with 26 under both the reference and P2. That two-person difference proves little, but it suggests the lower Ra cost P1 nothing in perceived naturalness.
Limits and product questions
The sample was small. People with advanced cataracts, glaucoma, or macular degeneration were excluded, removing many residents a memory care designer lights for. Chromaticity between the reference and test lights was not perfectly matched, and the naturalness question was a simple yes or no. The authors also warn against reading 300 lux as a recommendation.
Opple financially supported the study, according to the paper's disclosures. The paper names no product, but a news release distributed through Optica, the journal's publisher, says Opple is now working to translate the findings into lighting products. That makes the work early product development as much as academic research. The underlying data is available only on request, so independent replication matters.
The method requires at least four independently controlled LED channels. Multichannel color-mixing fixtures rarely appear in a care facility bid. Most products sold as tunable in healthcare and senior living adjust color temperature across two channels, which would not reproduce these spectra. That gap is an interpretation, not a claim in the paper.
For lighting people in senior living and healthcare, the study raises a pointed question. The industry's color metrics make no allowance for aging eyes, and a growing share of building occupants are well past middle age. If a tuned spectrum can help residents read a medication label or judge whether food has spoiled, the debate shifts to how quickly that evidence reaches specifications and product lines, and whose products get there first.