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Spectrally tunable light sources for general lighting have recently attracted much attention as versatile solutions that can be used in humancentric lighting implementations provided with excellent color rendering and increased user perception. However, temperature and age-dependent color shifts and flux variations in the light-emitting diode (LED) emission are nonresolved challenges that need to be overcome in order to be used in final applications. We demonstrate two strategies that can be used to efficiently and precisely generate arbitrary spectral power distributions (SPDs) using multichannel LED engines. First, we introduce different methods to match a given SPD and select an algorithm (simulated annealing) in virtue of its speed (in the milliseconds range) and accuracy (color shifts Δu ′ v ′

We explore methods that efficiently replicate arbitrary spectra with both high precision and accuracy using multichannel light-emitting diode (LED) lighting systems. It is well known that LED-based light sources deteriorate over time and change their spectral output with varying operating junction temperatures. A simple open-loop approach to the spectral matching problem would bring about unbearable spectral and color inaccuracies. In the literature, different solutions have been studied that make use of integrated spectrometers as closed-loop feedback elements that warrant spectral awareness and self-correction. However, the prohibitive cost of small spectrometers (that generally involve CMOS-based gratings) constitutes a high barrier that prevents their integration into final lighting products. We demonstrate how a cost-effective colorimeter can be used not only to preserve the color point of the target spectrum but also to keep the spectral matching error extremely low (relative spectral error u ′ v ′

Lasers and laser systems are a mature technology, yet there is a long road ahead for innovation and enthusiasm. We review some of the 40 years of R&D and manufacturing of lasers at ELOP-Elbit Systems. Bulk solid state lasers, for designators and range finders, as well as fiber lasers, for directed IR countermeasures and laser radar applications are described. These two technologies provide and will continue to offer a vast number of products for security and defense applications. Current and future generations of laser products will have higher average power together with improved beam quality, better efficiencies, and superior robustness all in a more compact package.

This PDF file contains the errata for “OE Vol. 44 Issue 11 Paper 2159010” for OE Vol. 44 Issue 11

White LED spectra for general lighting should be designed for high luminous efficacy as well as good color rendering. Multichip and phosphor-type white LED models were analyzed by simulation of their color characteristics and luminous efficacy of radiation, compared with those of conventional light sources for general lighting. Color rendering characteristics were evaluated based on the CIE Color Rendering Index CRI, examining not only Ra but also the special color rendering indices Ri, as well as on the CIELAB color difference Eab for the 14 color samples defined in CIE 13.3. Several models of three-chip and four-chip white LEDs as well as phosphor-type LEDs are optimized for various parameters, and some guidance is given for designing these white LEDs. The simulation analysis also demonstrated several problems with the current CRI, and the need for improvements is discussed. © 2005

Although lighting systems powered by photovoltaic (PV) cells have existed for many years, they are not widely used, especially in lighting for buildings, due to their high initial cost and low conversion efficiency. One of the technical challenges facing PV-powered lighting systems has been how to use the dc power generated by the PV module to energize common light sources that are designed to operate efficiently under ac power. Usually, the efficacy of dc light sources is very poor compared to ac light sources. Rapid developments in LED lighting systems have made this technology a potential candidate for PV-powered lighting systems. This study analyzed the efficiency of each component of PV-powered lighting systems to identify optimum system configurations for different applications.

The spectral properties of commercially available halogen and LED-based MR16s were investigated. The metrics used to characterize the MR16s include the total luminous flux (TLF), correlated color temperature (CCT), color-rendering index (CRI), angular variation of CCT, and luminous efficacy. The halogen MR16s were included as a baseline for comparison with LED-based MR16s. Seven LED-based MR16s were investigated, including three constructed from 5-mm LEDs, and four constructed from high-power devices based on a larger die. It is shown that MR16s constructed from white LEDs are not suitable as a direct replacement for existing alternatives at this time, due to their low power efficiency and poor TLF. MR16s constructed with a single phosphor also have poor CRIs and undesirable CCTs. An MR16 with an extra phosphor in the red region of the spectrum shows improvement in CRI and a lower CCT than the other LED-based MR16s. All of the LED-based MR16s had a variation of CCT that was larger than those of the halogen devices.

An optical model for simulating light extraction efficiency of a GaN-based LED chip is presented. We propose the introduction of a periodic sharpening structure on the interface between the sapphire and the n-GaN of a GaN-based LED to obtain as high as 78% light extraction efficiency.