A novel application of smart human centric lighting within the scope of energy efficiency and comfort assessment criteria

Abstract

his study investigates the impact of human centric lighting (HCL) in an open plan office environment at Istanbul Technical University. The research involved sixty participants in the first phase and twenty-four in the second phase. The primary objective was to evaluate individualized lighting solutions that comply with Circadian Stimulus (CS) and Equivalent Melanopic Lux (EML) metrics. During the first phase, single Correlated Color Temperature (CCT) Light Emitting Diode (LED) sources were used, while the second phase explored the effects of different CCTs. Preliminary findings indicated potential for energy-efficient lighting modifications, with phase two concentrating on optimizing lighting quality and ensuring comfort criteria were met. In the design development phase, the lighting design process was thoroughly outlined, including summaries of circadian lighting metrics, simulation tools, energy considerations, and the research plan for the circadian lighting open plan office. The study ensured that the design aligned with recommended thresholds for EML and CS, maintaining horizontal and vertical illuminance levels consistent with recommendations from the Illuminating Engineering Society (IES) for visual tasks. Based on the simulation study, two different light distribution curve luminaires, Direct Suspended Linear (L1) and Direct and Indirect Suspended Linear (L2), were chosen for the study. Additionally, threshold suspended mounting heights of 1.5m (L1) and 2.3m (H3), and one Optimum Luminaire Height (OLH) of 1.8m (L2) above the finished floor were defined for the lighting luminaires. The experimental aspect involved assessing changes in lighting levels, psychological comfort, and performance at three main target heights (H1, H2, H3) for both lighting scenarios (L1 and L2). Participants were asked to complete visual cognitive performance tests, proofreading tasks, and the Karolinska Sleepiness Scale (KSS) test across six different lighting scenarios during the first phase to assess the impact of lighting level changes on psychological comfort, and four different lighting scenarios during the second study phase. The experiment aimed to explore human-centered lighting conditions alongside physiological comfort conditions, using questionnaires (Q1 and Q2) to gather data on error quantities (E) and time periods (t) as measurement scales, alongside participants' preferences based on their comfort criteria. Key results indicated that participants' performance and visual perception varied significantly across different lighting conditions and heights. The performance evaluation compared participants' results between heights H1, H2, and H3 for both L1 and L2 scenarios. Significant p-values indicated differences in performance and psychological comfort based on lighting levels, luminaire positions, and light distribution beams. Notably, the performance of participants was significantly influenced by age, with distinct differences observed between age groups 20-30, 30-40, and above 40. Phase one of the study evaluates the lighting mounting height for human-centered lighting. A single CCT of 3800K was investigated to determine its influence on visual comfort and visual test responses. The scenarios of L1H3 and L2H2 were identified as the most successful. The most favorable scenario was observed in L1H3, both in terms of performance and participant preferences. Conversely, the results for L2H2 indicate that while participant performance was successful, their preference was lower compared to L2H3. Although L2H3 was preferable, L2H2 was selected for evaluation in phase two with CCTs of 2700K, 3800K, and 6000K. Phase two of the study focused on varying CCTs to investigate their influence on visual comfort and circadian response. L1 was assessed with a constant CCT of 3800K, while L2 examined CCTs of 2700K, 3800K, and 6000K, set at operation rates of 75%, 60%, and 40% of the total luminaire output, respectively. These configurations aimed to meet the minimum CS requirement of 0.3. Regarding EML values, L1 had an EML set at 358, while L2 exhibited varied results: 275.5 for 2700K, 293 for 3800K, and 319 for 6000K. The findings from phase two indicated dissatisfaction with the lighting set at 6000K, while warmer CCTs of 2700K likely had a positive impact due to the lower dimming rate meeting CS and EML requirements, resulting in higher illuminance levels on the desk compared to 3800K and 6000K scenarios. Participants clearly preferred higher heights (H3) for appealing lighting conditions, confirming the strong correlation among subjective evaluations of lighting scenarios such as color pleasantness, lighting satisfaction, and lighting heights. Overall, the study suggests that individualized lighting systems tailored to open plan office environments can enhance worker satisfaction and meet HCL requirements. Using consistent survey questions across different lighting concepts can help identify specific factors influencing CCT preferences. In conclusion, integrating individualized lighting systems in open plan offices aligns with HCL requirements, ensuring worker satisfaction and potentially improving performance. The findings provide insights for enhancing office lighting environments, emphasizing the importance of considering both energy efficiency and occupant comfort.