Solid-state lighting has made tremendous progress this past decade, with the potential to make much more progress over the coming decade. In this article, the current status of solid-state lighting relative to its ultimate potential to be “smart” and ultra-efficient is reviewed. Smart, ultra-efficient solid-state lighting would enable both very high “effective” efficiencies and potentially large increases in human performance. To achieve ultra-efficiency, phosphors must give way to multi-color semiconductor electroluminescence: some of the technological challenges associated with such electroluminescence at the semiconductor level are reviewed. To achieve smartness, additional characteristics such as control of light flux and spectra in time and space will be important: some of the technological challenges associated with achieving these characteristics at the lamp level are also reviewed. It is important to emphasise that smart and ultra-efficient are not either/or, and few compromises need to be made between them. The ultimate route to ultra-efficiency brings with it the potential for smartness, the ultimate route to smartness brings with it the potential for ultra-efficiency, and the long-term ultimate route to both might well be color-mixed RYGB lasers.

Toward Smart and Ultra-Efficient Solid-State Lighting

Light quantity (intensity and photoperiod) and quality (spectral composition) affect plant growth and physiology and interact with other environmental parameters and cultivation factors in determining the plant behaviour. More than providing the energy for photosynthesis, light also dictates specific signals which regulate plant development, shaping and metabolism, in the complex phenomenon of photomorphogenesis, driven by light colours. These are perceived even at very low intensity by five classes of specific photoreceptors, which have been characterized in their biochemical features and physiological roles. Knowledge about plant photomorphogenesis increased dramatically during the last years, also thanks the diffusion of light-emitting diodes (LEDs), which offer several advantages compared to the conventional light sources, such as the possibility to tailor the light spectrum and to regulate the light intensity, depending on the specific requirements of the different crops and development stages. This knowledge could be profitably applied in greenhouse horticulture to improve production schedules and crop yield and quality. This article presents a brief overview on the effects of light spectrum of artificial lighting on plant growth and photomorphogenesis in vegetable and ornamental crops, and on the state of the art of the research on LEDs in greenhouse horticulture. Particularly, we analysed these effects by approaching, when possible, each single-light waveband, as most of the review works available in the literature considers the influence of combined spectra.

/pdf/light-quality-manipulation-to-control-plant-growth-and-1whgw2s1bb.pdf

Light-Quality Manipulation to Control Plant Growth and Photomorphogenesis in Greenhouse Horticulture: The State of the Art and the Opportunities of Modern LED Systems

In this study, a comprehensive review focusing on key strategies of energy saving and climate control technologies for greenhouses is presented. Following the brief and concise assessment of existing greenhouse systems in terms of their role in total energy consumption; cost-effective, energy-efficient and environmentally friendly technologies are analyzed in detail for potential utilization in greenhouses for notable reductions in energy consumption and emission levels. The technologies considered within the scope of this research are mainly renewable and sustainable based solutions such as photovoltaic (PV) modules, solar thermal (T) collectors, hybrid PV/T collectors and systems, phase change material (PCM) and underground based heat storage techniques, energy-efficient heat pumps, alternative facade materials for better thermal insulation and power generation (heat insulation solar glass, PV glazing, aerogel and vacuum insulation panel, polycarbonate sandwich panels), innovative ventilation technologies using pre-heating and cooling (high performance windcatchers) and efficient lighting systems. The findings from the research clearly reveal that up to 80% energy saving can be achieved through appropriate retrofit of conventional greenhouses with a payback period of 4–8 years depending on climatic conditions and crop type.

Renewable and sustainable energy saving strategies for greenhouse systems: A comprehensive review

Solid‐state lighting is advancing toward higher power, higher brightness, and smaller size to cope with the market competitiveness, and laser‐driven solid‐state lighting technology is springing up owing to its super‐high brightness and compactness. These developments put forward new requirements for color conversion materials (i.e., phosphors). Here, the state‐of‐art achievements in laser phosphors are summarized, and the topics of luminescence saturation, light extraction efficiency, and light uniformity encountered in laser lighting technology are discussed. Several typical types of color converters, such as single crystal, phosphor ceramics, phosphor‐in‐glass, phosphor films, and quantum‐well light‐emitting diodes, are comparatively overviewed and discussed. The cutting‐edge applications of high‐brightness white laser light in lighting, displays, healthcare, and communications are summarized. The challenges and outlook in laser‐driven solid‐state lighting and some empirical rules for designing novel laser phosphors are highlighted.

Color Conversion Materials for High-Brightness Laser-Driven Solid-State Lighting

The aim of this review is to present the progress in preparing phosphorescent particles based on the reported research. We highlight the recent progress on SrAl 2 O 4 : Eu, Dy particles by describing the advantages and disadvantages of the different synthesis methods. This long-lasting material combines several favorable attributes: is stable, efficient, and less toxic that their predecessors. For that, large attention has been paid to the development of an efficient preparation method of SrAl 2 O 4 doped powders, including sol-gel method, hydrothermal synthesis, laser synthesis, combustion synthesis and solid state reaction. However, many of these techniques are not compatible with large-scale production and with the principles of sustainability. Industrial processing of highly crystalline powders usually requires high synthesis temperatures, typically between 1300 and 1900 °C, with long processing times, especially for solid state reaction. As a result, the average particle size is typically within the 20–100 µm range. This large particle size is limiting for current applications that demand sub-micron particles. The microstructure and size which are controlled through adjusting the experimental conditions have a great influence in the final photoluminescence response. Therefore, much effort has been devoted to exploring new strategies to obtain sub–micrometric particles, avoiding stringent, intricate, tedious, costly, or inefficient preparation steps and intrinsic toxicity or elemental scarcity. Moreover, persistent luminescent nanomaterials have attracted great interest to their potential application in solar cells, biological labeling and imaging and security encode. In addition, we describe the challenges and future of phosphorescent materials in regard to their synthesis, properties and applications. Finally, some further suggestions have been also addressed to enhance its photoluminescence response from the perspective of the synthesis. We believe that such a review can accelerate the developments of SrAl 2 O 4 -based materials.

Long lasting phosphors: SrAl2O4:Eu, Dy as the most studied material

Light energy is an important factor for plant growth. In regions where the natural light source (solar radiation) is not sufficient for growth optimization, additional light sources are being used. Traditional light sources such as high pressure sodium lamps and other metal halide lamps are not very efficient and generate high radiant heat. Therefore, new sustainable solutions should be developed for energy efficient greenhouse lighting. Recent developments in the field of light source technologies have opened up new perspectives for sustainable and highly efficient light sources in the form of LEDs (light-emitting diodes) for greenhouse lighting. This review focuses on the potential of LEDs to replace traditional light sources in the greenhouse. In a comparative economic analysis of traditional vs. LED lighting, we show that the introduction of LEDs allows reduction of the production cost of vegetables in the long-run (several years), due to the LEDs׳ high energy efficiency, low maintenance cost and longevity. In order to evaluate LEDs as an alternative to current lighting sources, species specific plant response to different wavelengths is discussed in a comparative study. However, more detailed scientific studies are necessary to understand the effect of different spectra (using LEDs) on plants physiology. Technical innovations are required to design and realize an energy efficient light source with a spectrum tailored for optimal plant growth in specific plant species.

LEDs for energy efficient greenhouse lighting

Photodarkening of Yb-doped aluminosilicate fibers by continuous wave 488 nm irradiation was investigated. The irradiation induced significant excess loss in the UV-visible spectroscopy (VIS) region in Yb-doped aluminosilicate fibers while pure aluminosilicate fibers showed negligible induced loss. Ultraviolet-VIS-near infrared spectroscopy revealed an absorption peak at 220 nm in unexposed Yb-doped aluminosilicate fiber preforms. The observed peak was attributed to Yb-associated oxygen deficiency centers (ODCs) and proposed as a precursor of the photodarkening. The proposed model was supported by measurements on oxygen loaded Yb-doped aluminosilicate fibers. In these, the photodarkening could be significantly reduced, which we attribute to a smaller number of ODCs following oxygen loading.

Photodarkening in Yb-doped aluminosilicate fibers induced by 488 nm irradiation

Abstract Contemporary white light-emitting diodes (LEDs) are much more efficient than compact fluorescent lamps and hence are rapidly capturing the market for general illumination. LEDs are also replacing halogen lamps or even newer xenon based lamps in automotive headlamps. Because laser diodes are inherently much brighter and often more efficient than corresponding LEDs, there is great research interest in developing laser diode based illumination systems. Operating at higher current densities and with smaller form factors, laser diodes may outperform LEDs in the future. This article reviews the possibilities and challenges in the integration of visible laser diodes in future illumination systems.

https://www.degruyter.com/downloadpdf/j/aot.2013.2.issue-4/aot-2013-0031/aot-2013-0031.xml

Lighting with laser diodes

In response to the Comment, we show that Engholm et al. [Opt. Lett. 33, 1216 (2008)] misinterpret the absorption peak at 230 nm and reach mistaken conclusions that contradict their experimental results. Differences in compositions and fabrication details mean that their results are only marginally relevant to our experiments [Opt. Lett. 32, 1626 (2007)]. The excitation of electrons to a charge-transfer band around 230 nm in Yb-doped aluminosilicate glasses leads to conversion from Yb, which, in our opinion, is more likely to account for photobleaching rather than photodarkening.

Reply to comment on “Photodarkening in Yb-doped aluminosilicate fibers induced by 488 nm irradiation”

Photodarkening in highly Yb-doped aluminosilicate and phosphosilicate fibers, under 488 nm irradiation, is presented. Both irradiation-induced excess loss and post-irradiation temporal loss evaluations reveal that Yb-doped phosphosilicate fiber is highly resistant to photodarkening.

488 nm irradiation induced photodarkening study of Yb-doped aluminosilicate and phosphosilicate fibers

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