Energy efficiency and color quality limits in artificial light sources emulating natural illumination

Real-Time Investigations and Simulation on the Impact of Lighting Ambience on Circadian Stimulus

Indoor lighting, incorporated with visual and circadian needs, is the upcoming goal of lighting designers. In tropical and subtropical regions, where more daylight is available, daylight harvesting is a prime source of ambient lighting indoors. This paper aims to study various cases of lighting ambience to investigate the circadian lighting capability in terms of the circadian stimulus (CS) of the system under consideration. The instances considered are simulation studies in an open office plan and real-time experimentations in a test workbench and a faculty cabin. Daylight integration was undertaken through controlled venetian blinds, tunable sources and a commercially available human-centric lighting system. The result and analysis show the influence of spectrally tunable light sources on CS rather than fixed light sources. Due to the varying CCT of tunable LED luminaire, circadian stimulation for an occupant can be easily incorporated without crossing the limits of vertical and horizontal illuminance, which may lead to visual discomfort. The findings from this study reveal that daylight–artificial light integration scheme with controlled shading and spectrally tunable source provides the optimal solution for glare-free, energy-effective and circadian entrainment, i.e. human-centric lighting (HCL). With the help of simulations, pre-evaluation will aid the lighting engineers in making a better choice among the various lighting-controlled schemes to implement HCL in indoor office spaces.

Sr[Li2Al2O2N2]:Eu2+-A high performance red phosphor to brighten the future

Innovative materials for phosphor converted white light-emitting diodes are in high demand owing to the huge potential of the light-emitting diode technology to reduce energy consumption worldwide. As the primary blue diode is already highly optimized, the conversion phosphors are of crucial importance for any further improvements. We report on the discovery of the high performance red phosphor Sr[Li2Al2O2N2]:Eu2+ meeting all requirements for a phosphor's optical properties. It combines the optimal spectral position for a red phosphor, as defined in the 2016 Research & Development-plan of the United States government, with an exceptionally small spectral full width at half maximum and excellent thermal stability. A white mid-power phosphor-converted light-emitting diode prototype utilising Sr[Li2Al2O2N2]:Eu2+ shows an increase of 16% in luminous efficacy compared to currently available commercial high colour-rendering phosphor-converted light-emitting diodes, while retaining excellent high colour rendition. This phosphor enables a big leap in energy efficiency of white emitting phosphor-converted light-emitting-diodes.

Optimizing indoor illumination quality and energy efficiency using a spectrally tunable lighting system to augment natural daylight

This article demonstrates the benefits of complementing a daylight-lit environment with a spectrally tunable illumination system. The spectral components of daylight present in the room are measured by a low-cost miniature spectrophotometer and processed through a number of optimization algorithms, carefully trading color fidelity for energy efficiency. Spectrally-tunable luminaires provide only those wavelengths that ensure that either the final illumination spectrum inside the room is kept constant or carefully follows the dynamic spectral pattern of natural daylight. Analyzing the measured data proves that such a hybrid illumination system brings both unprecendented illumination quality and significant energy savings.