Assessing the Effects of Illuminance and Correlated Color Temperature on Emotional Responses and Lighting Preferences Using Virtual Reality

This paper presents a novel approach to assessing human lighting adjustment behavior and preference in diverse lighting conditions through the evaluation of emotional feedback and behavioral data using VR. Participants (n= 27) were exposed to different lighting (n=17) conditions with different levels of illuminance and correlated color temperature (CCT) with a randomized order in a virtual office environment. Results from this study significantly advanced our understanding of preferred lighting conditions in virtual reality environments, influenced by a variety of factors such as illuminance, color temperature, order of presentation, and participant demographics. Through a comprehensive analysis of user adjustment profiles, we obtained insightful data that can guide the optimization of lighting design across various settings

Subjective preference of light colour and LED lighting

The main objective of this work is to investigate the subjective preferences for lighting environments under different LED spectral power distributions (SPDs) and to analyse the different existing colour quality descriptors in order to recommend the best descriptor. An additional aim of the work is to find out the correlated colour temperature (CCT) and illuminance levels that users prefer for LED lighting. The experiments were conducted in lighting booths and in office rooms, where the subjective preferences for different LED light spectra were studied. In the lighting booth experiments, seven different LED SPDs were studied at CCTs of 2700 K, 4000 K and 6500 K at 500 lux. The study showed that the observers preferred the LED SPDs which increased the object chroma and colourfulness values (calculated in CIECAM02-UCS). Also, the preferred LED SPDs had higher values of reference-based metrics (such as colour quality scale (CQS) colour preference scale) and higher values of area-based metrics (such as CQS colour gamut scale or gamut area index (GAI)). The observers preferred the light sources at CCT of 4000 K and 6500 K over the CCT of 2700 K. The work was continued by simulation work and user acceptance studies to find out the simplified LED SPDs that the observers would prefer. The simulation results suggested that it is possible to generate simplified LED SPDs that have CQS Qp and CQS Qg values similar to those of the preferred complex SPDs that were generated by 9 to 11 different types of LEDs. The user acceptance studies conducted in the lighting booths also showed that the simplified LED SPDs using three different types of LEDs were preferred over complex LED SPD. Later, similar simplified LED SPDs were also studied in office rooms, and it was found that the observers preferred simplified LED SPDs over fluorescent lamp. The three different LED SPDs at each CCT of 4000 K and 6500 K were studied in the office room experiments. The observers preferred most the LED SPDs with high CQS Qp and CQS Qg or GAI values and least the LED SPDs that had the lowest CQS Qp and CQS Qg values. Also, the light sources (having high CQS Qp and CQS Qg) with negative Duv values were more preferred over light sources with positive Duv values maintaining the Duv values within the limit of ±0.0054. Moreover, for the office lighting, the observers preferred CCT of 4000 K over CCT of 6500 K at 500 lux. It was also found that the observers preferred the illuminance level of 500 lux over 300 lux. The results of the experiments conducted in the lighting booths to test the performance of different fidelity metrics showed that the CIE CRI, CRI2012 and CQS provide similar predictions for LED light sources that do not enhance the object chroma. It was found that the best prediction of colour fidelity was provided by CQS for LED light sources that enhance object chroma

User acceptance studies for LED office lighting: light spectrum and correlated colour temperature

During the last decade, lighting technology based on light-emitting diodes (LEDs) has advanced rapidly and is paving the way for the application of LED lighting in offices. Two experiments were carried out to study user preference for different LED light spectra and correlated colour temperature (CCT), and to determine user acceptance for LED office lighting. In a lighting booth experiment, twenty one different LED spectral power distributions (SPDs) were realised considering colour quality scale (CQS) gamut area scale Qg, CQS Colour preference scale Qp, feeling of contrast index (FCI) along with the CIE colour rendering index (CRI) at the CCTs of 2700K, 4000K, and 6500K. The observers evaluated the lit scenes under different light spectra at 500 lux for different factors such as brightness, visual comfort, and pleasantness. The observers preferred the LED SPDs which had higher values of a reference-based metric (Qp) or higher values of an area-based metric (Qg). The chromaticity difference (Duv) values also influenced the user preference of the light spectra. The observer preferred the CCT of 4000K and 6500K to the CCT of 2700K at 500 lux. The findings of the lighting booth experiment were used as the base line for the office room experiment where six different LED SPDs were realised at the CCTs of 4000K and 6500K considering Qp, Qg, and FCI. The observers evaluated the lit environments under different SPDs for brightness, visual comfort, glare, and pleasantness of colour of light along with other lighting aspects at illuminance levels of 300 lux and 500 lux. At 4000K, the observers preferred the LED light spectra which had higher values of Qp and Qg to the fluorescent lamps in the office environment at 500 lux. The preferred LED SPDs had negative Duv values, whereas the fluorescent lamp had positive Duv values. The observers preferred the CCT of 4000K to 6500K, under which the observers felt more comfortable and found the colour of light more pleasant than under 6500K at 500 lux. It was also found that the lit environment should be able to provide good quality lighting for visibility and the observers should feel visually comfortable in that lit environment if the illuminance level is varied. The results indicate the need to develop LED light spectra for office lighting considering Qp and Qg with negative Duv values within the recommended limit. As the Duv values affected the observers' preferences, colour of white light should be characterised not only by CCT but also by Duv values

A revised Kruithof graph based on empirical data

Kruithof’s graph identifies combinations of illuminance and correlated color temperature (CCT) alleged to yield pleasing visual conditions for interior lighting. Though in research terms the support provided by Kruithof is insufficient, it is widely cited as a design rule and has been the focus of many experimental studies despite evidence against Kruithof since at least 1990. The current article examines the trends displayed in those studies considered to provide credible evidence: these do not support Kruithof. For pleasant conditions, these data suggest only avoiding low illuminances and do not favor any CCT

Aging-In-Place Home Modification: LED Lamp Color Temperature Preference Among Adults

This study evaluated LED color temperature preference and effectiveness in a task light setting for older adults with a comparison to younger adults. Test subjects included visually active adults, male and female, from 19 years to 96 years of age. The researcher tested one hundred participants from several test sites. The researcher ascertained conclusions based on the correlations of age, gender, visual acuity, time of day, and visual medical conditions to LED preference. A tunable lamp with four correlated color temperatures (CCT/K), 2700K, 3500K, 4100K, and 5000K was analyzed using timed and graded, reading and number comparison tasks. Lumen output between the correlated color temperatures was adjusted for consistency to prevent illuminance (lumens) from effecting the outcome. Test subjects choose a preferred correlated color temperature and completed a subjective survey accessing the preferred comfort level. Results indicated the test subjects performed better with the 4100K correlated color temperature. Regarding personal preference of correlated color temperature by test subjects on average: the 4100K correlated color temperature was preferred first (36%), the 3500K correlated color temperature was preferred second (28%), the 5000K was preferred third (24%), and the 2700K was preferred least (12%). A significant difference was discovered between men and women with men, on average, taking longer to complete the reading and number matching tasks than women

Personal control of correlated color temperature of light:Effects on thermal comfort, visual comfort, and cognitive performance

Recent studies have suggested that thermal and visual comfort are correlated, although the causality underlying this correlation is unclear. Personal control of correlated color temperature (CCT) provides individual visual comfort, but its effects on other parameters such as thermal comfort and cognitive performance remain underexamined. Therefore, we investigated if personal control of CCT can, on top of visual comfort, enhance thermal comfort and cognitive performance in office scenarios while exposed to mild cold (17 °C) using a 2x2 within-subject design. Sixteen participants were initially exposed to CCT of either 2700 K or 5700 K for 70 min. In the subsequent 70 min, participants either had free control of CCT or no control. As expected, personal control of CCT improved visual comfort and mitigated perceived eye-related symptoms. However, it did not significantly affect thermal comfort for either antecedent CCT. When the antecedent CCT was 5700 K, personal control of CCT increased alertness and physiological arousal, improved the planning and verbal cognitive performance, but, unexpectedly, decreased performance on mental spatial manipulation tasks. Additional analyses then explored the role of the psychological and personalization effects of personal control by controlling for the actual CCT. These suggest that control benefited visual comfort, eye-related symptoms, perceived task performance, pleasure, alertness and physiological arousal. This study is one of the first studies to demonstrate that visual comfort does not causally affect thermal comfort. Personal control of CCT benefits visual appraisals and eye-related symptoms, sometimes improves alertness, but differentially influences cognitive performance depending on the task type.</p