Michael P. Royer

Light Therapy for Seniors in Long Term Care

OBJECTIVES To investigate the effects of light therapy on cognition, depression, sleep, and circadian rhythms in a general, nonselected population of seniors living in a long term care facility. DESIGN A double-blind, placebo-controlled trial. SETTING The experiment took place at a long term care facility in Pennsylvania. PARTICIPANTS Study participants (15 treatment, 13 placebo) were residents receiving either personal care or skilled nursing care. INTERVENTION Treatment consisted of approximately 400 lux of blue light administered for 30 minutes per day, Monday through Friday, for 4 weeks. The placebo was approximately 75 lux of red light generated from the same device. MEASUREMENTS Behavioral assessments were made using the MicroCog Assessment of Cognitive Functioning, Geriatric Depression Scale, and Profile of Mood States. Daytime sleepiness was evaluated using the Epworth Sleepiness Scale. RESULTS Three of the 4 composite scores from the MicroCog as well as the mean Tension/Anxiety score from the Profile of Mood States showed a significant treatment versus placebo effect. CONCLUSION Blue light treatment led to significant cognitive improvements compared with placebo red light and may be a promising environmental intervention to reduce cognitive symptoms in elderly, long-term care residents.

A Test of the S/P Ratio as a Correlate for Brightness Perception using Rapid-Sequential and Side-by-Side Experimental Protocols

Abstract An experiment was performed to: 1) Test the hypothesis that the ratio P*(S/P)0.5 can be used to predict the perception of spatial brightness, and 2) directly compare the rapid-sequential and side-by-side evaluation modes for assessing spatial brightness. The two evaluation modes produced comparable results. Though the side-by-side method has in the past been questioned by others, the data herein illustrates that it is neither faulty nor invalid. Red, green, and blue LEDs were employed to create four light settings that were permutations of two S/P ratios (1.7 and 2.6) and two luminance levels (24 and 30 cd/m2). The S/P ratios corresponded to the practical extremities of CCT (2900 and 7200 K) and were structured to have their chromaticity on the blackbody locus. At equal luminance there was no difference in the perception of brightness, irrespective of CCT. At unequal luminance, but when the ratio of P*(S/P)0.5 was set to 1:1, brightness perception was predicted by luminance. These data suggest that spatial brightness perceptions at photopic light levels are unrelated to the S/P ratio of the illumination. These results are consistent with the “prime color” theory of vision that is rooted in the trichromatic nature of human vision.

Spatial Brightness Perception of Trichromatic Stimuli

Abstract An experiment was conducted to examine the effect of tuning optical radiation on brightness perception for younger (18–25 years of age) and older (50 years of age or older) observers. Participants made forced-choice evaluations of the brightness of a full factorial of stimulus pairs selected from two groups of four metameric stimuli The large-field stimuli were created by systematically varying either the red or the blue primary of an RGB LED mixture. The results indicate that light stimuli of equal illuminance and chromaticity do not appear equally bright to either younger or older subjects. The rank-order of brightness is not predicted by current models of human vision or theories of brightness perception including scotopic to photopic or cirtopic to photopic ratio theory, prime color theory, correlated color temperature, V(λ)-based photometry, color quality metrics, linear brightness models, or color appearance models. Age may affect brightness perception when short-wavelength primaries are used, especially those with apeak wavelength shorter than 450 nm. The results suggest the need for the further development of a metric (or metrics) to predict brightness perception and that age should be included as a variable in such models.

Human perceptions of colour rendition vary with average fidelity, average gamut, and gamut shape

An experiment was conducted to evaluate how subjective impressions of a light source’s colour quality depend upon the details of the shifts it causes in the colour appearance of illuminated objects. Twenty-eight participants each evaluated 26 lighting conditions in a 3.1 m by 3.7 m room filled with objects selected to cover a range of hue, saturation, and lightness. IES TM-30-15 Fidelity Index (Rf) values ranged from 64 to 93, IES TM-30 Gamut Index (Rg) values ranging from 79 to 117, and IES TM-30 red chroma shift (Rcs,h1) values ranging from −19% to 26%. All lighting conditions had the same nominal illuminance and chromaticity. Participants were asked to rate each condition on eight point scales for saturated–dull, normal–shifted, and like–dislike, as well as classifying the condition as one of saturated, dull, normal, or shifted. The findings suggest that gamut shape is more important than average gamut area for modeling human preference, with red playing a more important role than other hues. Average fidelity alone is a weak predictor of human perception, especially CIE Ra. Nine of the top 12 rated products had a CIE Ra value of 73 or less, which indicates that the criteria of CIE Ra ≥ 80 may be excluding many preferred light sources.

The Role of Presented Objects in Deriving Color Preference Criteria from Psychophysical Studies

ABSTRACT  Although it is a critical component of any measure of color rendition, a standardized set of color samples can seldom perfectly match a real space or a real set of observed objects. This means that there will always be some level of mismatch between predicted and observed color shifts. This article explores how the color distortions of three object sets that could be used in experiments compare to the color distortions predicted using the color evaluation samples of IES TM-30-15 (TM-30). The experimental object sets include those from a recent experiment [Royer and colleagues 2016], a set of produce (10 fruits and vegetables), and the X-Rite ColorChecker Classic. This numerical analysis focuses on the range of differences between viewed and characterized color shifts—using the TM-30 fidelity index (Rf), the TM-30 gamut index (Rg), and an alternative to Rg based on ΔC in CIECAM02—over a set of 344 spectral power distributions. The differences depended on the average chroma and spectral features of the sample set. The substantial range of differences shown for the produce and the ColorChecker means that design criteria for color rendition derived using these sample sets are less reliable. Specifiers should carefully consider how average measures of color rendition are applied to real spaces, and experimenters should carefully select experimental objects to avoid mischaracterizations.

Lumen Maintenance and Light Loss Factors: Consequences of Current Design Practices for LEDs

Abstract Light loss factors are used to help lighting systems meet quantitative design criteria throughout the life of the installation, but they also carry ancillary consequences, such as influencing first cost and energy use. As the type of light sources being specified continues to evolve, it is an appropriate time to evaluate the methods used in calculating light loss factors and understand the broad effects of performance attributes like lumen maintenance. Because of the unique operating characteristics of light emitting diodes (LEDs) and lack of a comprehensive lifetime rating—as well as the problematic relationship between lifetime and lumen maintenance—determining an appropriate lamp lumen depreciation (LLD) factor for LED products is difficult. The IES recommends using an LLD of not greater than 0.70 when quantity of light is an important design consideration. This approach deviates from the typical practice for conventional sources of using the ratio of mean to initial lumen output and may misrepresent actual performance, increase energy use, and inhibit comparisons between products. This article discusses the complications related to LLD and LEDs, compares the performance of some conventional and LED products, and examines alternatives to the current recommended approach for determining LLDs for LED products.

What Is the Reference? An Examination of Alternatives to the Reference Sources Used in IES TM-30-15

ABSTRACT This article documents the role of the reference illuminant in the IES TM-30-15 method for evaluating color rendition. TM-30-15 relies on a relative reference scheme; that is, the reference illuminant and test source always have the same correlated color temperature (CCT). The reference illuminant is a Planckian radiator, model of daylight, or combination of those two, depending on the exact CCT of the test source. Three alternative reference schemes were considered: (1) either using all Planckian radiators or all daylight models, while maintaining the CCT match of the test and reference; (2) using only one of 10 possible illuminants (Planckian, daylight, or equal energy), regardless of the CCT of the test source; (3) using an off-Planckian reference illuminant (that is, a source with a negative Duv). No reference scheme is inherently superior to another, with differences in metric values largely a result of small differences in gamut shape for the reference alternatives. Though using any of the alternative schemes is more reasonable in the TM-30-15 evaluation framework than it was with the CIE Test Color Method, the differences still ultimately manifest only as changes in interpretation of the results. Reference illuminants are employed in TM-30 to provide a familiar point of comparison, not to establish an ideal source.

IES TM-30-15 Is Approved—Now What?

Address correspondence to Michael P. Royer, Pacific Northwest National Laboratory, 620 SW 5th Ave., Suite 810, Portland, OR 97204, USA. E-mail: michael.royer@pnnl.gov

Human perceptions of colour rendition at different chromaticities

An experiment was conducted to evaluate how perceptions of a light source’s colour quality depend upon colour rendition and chromaticity. Thirty-four participants each evaluated 50 lighting scenes in a 3.7 m by 5.5 m room filled with objects. The lighting scenes included five chromaticity groups, with 10 systematically-varied colour rendition conditions repeated in each group. Participants, who chromatically adapted to each chromaticity group, were asked to rate each scene on eight point scales for saturated-dull, normal-shifted and like–dislike (preference), as well as choosing whether they found the scenes to be acceptable or unacceptable. The findings suggest that colour rendition perceptions can vary with chromaticity, with an interactive effect of correlated colour temperature and Duv. The same IES TM-30-15 measures, Fidelity Index (IES Rf), Gamut Index (IES Rg) and hue-angle bin 16 (Red) Local Chroma Shift (IES Rcs,h16), could be used to effectively model perceptions within each chromaticity group, and provided suitable performance for the overall set of 50 conditions. The differences in ratings between the chromaticity groups were substantially smaller than the range in ratings for the 10 colour rendition conditions within each group, allowing the same acceptability-based criteria of IES Rf ≥ 75, IES Rg ≥ 98 and −7% ≤ IES Rcs,h16 ≤ 15% to be applied to all chromaticity groups.

Correspondence: In support of the IES method of evaluating light source colour rendition

Fil: Tonello, Graciela Lucia del Carmen. Consejo Nacional de Investigaciones Cientificas y Tecnicas. Centro Cientifico Tecnologico Tucuman. Instituto de Investigacion En Luz, Ambiente y Vision; Argentina