Osram Sylvania

This study explores the possibility to dynamically modulate lighting spectra in a continuous manner such that luminous intensity remains constant but color rendering properties fluctuate as a function of time. The objective is for these changes to be subtle enough to not be consciously noticed by retail shoppers, but still stimulating enough so that colorful packaging designs will fluctuate in appearance so that shoppers' eyes may be subconsciously drawn randomly toward products just outside of a shopper's focus of attention. In this way, it is proposed that use of strategically modulated lighting conditions can, on average, increase shoppers' spatial range of browsing. An exploratory eye tracking study with 35 subjects was conducted. Results suggest a gender specific effect and demonstrate how lighting conditions can be used to partially neutralize this gender specific difference.

The main contribution of this study is to show the effect of light-emitting diode (LED) modelling in the design of offline drives. The authors propose the use of a source voltage and resistance model (SVRM), consisting of a threshold voltage source in series with the characteristic resistance, for the modelling of the LED. The offline drive used for the analysis is the flyback converter operating in discontinuous conduction mode. The equivalent circuit is analysed by superposition and the AC circuit is analysed with phasors. The analysis has proven that the flyback converter can be modelled as a current source feeding the output capacitor in parallel with the load. Likewise, the analysis demonstrated that the current ripple is always greater than the voltage ripple when an LED is used as a load. In order to validate the theoretical analysis, a design methodology for the flyback converter with the SVRM as a load was developed. The designed circuit was simulated in Spice and implemented in a prototype. Experimental results using an LED as load are compared with the same circuit using a simple resistance as load. The experimental results confirm the theoretical analysis with an error of <6.6%.

In this study, we report the fabrication, characterization, and modeling of a zigzag nanorod-structured graded-index antireflection coating fabricated by the oblique angle deposition (OAD) method. The optical properties of the reported coating were engineered by sculpting its composition and morphology using OAD, and the coating was designed to work with high-index, YAG:Ce ceramic phosphor plates. The coating enhances the normal-direction transmission of the phosphor plate over the broad visible-light spectrum. At 764 nm, the transmission is enhanced by 7.82%, compared to a potential maximum enhancement of 8.53%. For 633-nm light incident at 5°, the reported coating was measured to induce scattering loss of no greater than 1.27%. We developed a mathematical model that can use the OAD morphology information, developed from the film growth mechanism, as input parameters to simulate the optical properties of the nanostructured coatings. A finite-difference time-domain (FDTD) simulation was able to capture the polarization-dependent, antireflective performance of the coating, and the simulated transmission spectrum was in good agreement with both the measured spectrum and the spectrum calculated using the measured effective refractive indices in a transfer matrix formulation. In addition, the FDTD model was applied to predict the scattering losses. The simulation supports the experimental results and shows that the coating induces very weak scattering loss.

LEDs, which are rapidly replacing the traditional light sources for general illumination, present unique challenges with respect to flicker, due to their different electrical behavior in the circuits in which they are embedded. Since the present-day electrical systems are AC, there is potential for LED output to be time varying, because driver electronics are almost always employed and because driver and mains are not ideal. For flicker, time varying light is not an issue if it is not perceived by humans. The human perception aspect introduces enormous complexities, but large body of psychophysics research over many decades has shed much light on this. There now exist well known and recognized standards which provide for the measure and quantification of flicker. This paper offers a general technical perspective on flicker with discussions of each of these topics. (C) The Author(s) 2019. Published by ECS.

Light extraction from luminescent materials, where luminescence generated in a high refractive index medium must be coupled to a lower index medium, is a complex problem with significant ramifications for efficient LED and phosphor converted LED lighting. We derive thermodynamic arguments which show that light transmission for incident Lambertian light through arbitrary structured or non-structured surfaces is always limited by the ratio of incident to output etendues. Numerical simulations of various strongly scattering surfaces in the wave-optic regime are made to confirm the surface extraction results. The results are also extended to arbitrary angular radiance distributions of incident light as in Lenef, et al. [Opt. Lett., 39, 3058 ( 2014)], but also generalized to cases of restricted angular output emission. Furthermore, we show how cavity effects and scattering are both needed to overcome the thermodynamic surface extraction limits. Examples of both surface scattering and a converted LED with volume scattering are given. Finally, a derivation of the Lambertian light transmission theorem is developed from scalar wave-optics to highlight the physics of the thermodynamic result and to provide limits of applicability of the surface extraction limit. (c) The Author(s) 2018. Published by ECS.