KEYWORDS: Light sources and illumination, LED lighting, Clouds, Light sources, Light emitting diodes, Lamps, Data modeling, Luminescence, Control systems, Visualization
In recent years, LED lighting became an indispensable alternative to conventional lighting systems. Sophisticated
solutions offer not only comfortable white light with a good color rendering. They also provide the possibility of
changing illuminance and color temperature. Some systems even simulate daylight over the entire day, some including
natural variations as due to clouds. Such systems are supposed to support the chronobiological needs of human and to
have a positive effect on well-being, performance, sleep-quality and health.
Lighting can also be used to support specific aims in a situation, like to improve productivity in activation or to support
recreation in relaxation. Research regarding suitable light-settings for such situations and superordinate questions like
their influence on well-being and health is still incomplete.
We investigated the subjective preferences of men and women regarding light-settings for activation and relaxation. We
supplied two rooms and four cubes with light sources that provide the possibility of tuning illuminance, color
temperature and deviation from Plackian locus. More than 80 individuals – belonging to four groups differing in gender
and age – were asked to imagine activating and recovering situations for which they should adjust suitable and pleasant
lighting by tuning the above mentioned light properties. It was shown that there are clear differences in the lighting
conditions preferred for these two situations. Also some combined gender- and age-specific differences became apparent.
Typically, light emission from light-emitting diodes (LEDs) occurs under a broad range of angles. On the other hand, for a lot of applications a more directed light emission is desired. This can be realized with the use of additional optical elements, like lenses. Still, this may provide some complications in case of light sources consisting of a plurality of individual LEDs, e.g., a panel light, which is expected to illuminate a target area homogenously. Instead of a homogeneous illumination, the use of lenses is prone to give reason for an inhomogeneous light distribution in which the emission from the individual LEDs is easily distinguishable. Therefore, there is a strong request for alternative strategies of beam shaping of LED light in LED-luminaires targeting both on a directed as well as homogeneous illumination of an area. In this contribution we discuss an alternative approach in this regard: Firstly, a collimator is designed, which strongly directs the light emitted from a single LED light source. Subsequently, a foil with an optical structure, that can be fabricated in a cost-effective way by soft-lithography and which diffuses the collimated light again, is applied on the collimator. The optical structure and the respective amount of light diffusion are designed in a way that the desired radiation patterns both from a single as well as a plurality of LED sources can be realized. In addition, we show that the realization of a desired radiation profile is not the only advantage of such an approach. A key benefit of this concept is the possibility to reduce the angle dependent inhomogeneity
For a systematic approach to improve the white light quality of phosphor converted light-emitting diodes (LEDs) for general lighting applications it is imperative to get the individual sources of error for color temperature reproducibility under control. In this regard, it is imperative to understand how compositional, optical and materials properties of the color conversion element (CCE), which typically consists of phosphor particles embedded in a transparent matrix material, affect the constancy of a desired color temperature of a white LED source. In this contribution we use an LED assembly consisting of an LED die mounted on a printed circuit board (PCB) by chip-on-board technology and a CCE with a glob-top configuration as a model system and discuss the impact of potential sources for color temperature deviation among individual devices. Parameters that are investigated include imprecisions in the amount of materials deposition, deviations from the target value for the phosphor concentration in the matrix material, deviations from the target value for the particle sizes of the phosphor material, deviations from the target values for the refractive indexes of phosphor and matrix material as well as deviations from the reflectivity of the substrate surface. From these studies, some general conclusions can be drawn which of these parameters have the largest impact on color deviation and have to be controlled most precisely in a fabrication process in regard of color temperature reproducibility among individual white LED sources.
For a systematic approach to improve the white light quality of phosphor converted light-emitting diodes (LEDs) for general lighting applications it is imperative to get the individual sources of error for correlated color temperature (CCT) reproducibility and maintenance under control. In this regard, it is of essential importance to understand how geometrical, optical and thermal properties of the color conversion elements (CCE), which typically consist of phosphor particles embedded in a transparent matrix material, affect the constancy of a desired CCT value. In this contribution we use an LED assembly consisting of an LED die mounted on a printed circuit board by chip-on-board technology and a CCE with a glob-top configuration on the top of it as a model system and discuss the impact of the CCE shape and size on CCT constancy with respect to substrate reflectivity and thermal load of the CCEs. From these studies, some general conclusions for improved glob-top design can be drawn.
Color temperature constancy and color temperature maintenance are key issues in the context of the utilization of light-emitting diodes (LEDs) for general lighting applications. For a systematic improvement, it is imperative to understand how compositional, optical and thermal properties of the color conversion elements (CCE), which typically consist of phosphor particles embedded in a transparent matrix material, affect the constancy of a desired color temperature of a white LED source under operation. In particular, thermal stress, like a distinct thermal load of the CCEs under operation may also cause notable color shifts. In order to gain a better understanding of the thermal behavior of CCEs under operation, in this contribution we give by means of a combined optical and thermal simulation procedure a comprehensive discussion on the impact of different CCE shapes and sizes on their thermal responses.
Color constancy and color maintenance are key issues in the context of the utilization of light-emitting diodes (LEDs) for general lighting applications. For a systematic approach to improve the white light quality of phosphor converted LEDs and to fulfill the demands for color temperature reproducibility and constancy, it is imperative to understand how compositional, optical and thermal properties of the color conversion elements (CCE), which typically consist of a
phosphor particles embedded in a transparent matrix material, affect the correlated color temperature of a white LED
source. Based on a combined optical and thermal simulation procedure, in this contribution we give a comprehensive
discussion on the underlying coherences of light absorption, quantum efficiency and thermal conductivity and deduce
some strategies to minimize the temperature increase within the CCE in order to maintain acceptable color variations
upon device operation.
For a systematic approach to improve the white light quality of phosphor converted light-emitting diodes (LEDs) for
general lighting applications it is imperative to get the sources of error for color constancy under control. In this context,
it is essential to gain a deeper insight how the individual components of an LED package may contribute to color
deviation. Typically, both monochromatic and phosphor converted light-emitting diodes are finally encapsulated by a
pristine silicone layer in order to prevent mechanical damage of the LED packages. In this contribution we focus on the
shapes of such encapsulation layers and discuss, based on an optical simulation procedure, their impact on the color
temperatures of phosphor converted white LEDs as well as the ramifications of manufacturing imprecision of these
shapes on the constancy and reproducibility of a desired color temperature.
Key market requirements for white LEDs, especially in the general lighting and automotive
headlamp segments call for improved concepts and performance of white LEDs based on phosphor
conversion.
Major challenges are small emission areas, highest possible intensities, long-term color stability, and
spatial homogeneity of color coordinates. On the other hand, the increasingly high radiation power of
the blue LEDs poses problems for all involved materials. Various thick film coating technologies are
widely used for applying the color conversion layer to the semiconductor chip. We present novel
concepts based on Silicate phosphors with high performance in terms of spatial homogeneity of the
emission and variability of the color temperature. Numerical calculation of the optical properties
with the help of state-of-the-art simulation tools was used as a basis for the practical optimization of
the layer geometries.
At present, light-emitting diode (LED) modules in various shapes are developed and designed for the general lighting, advertisement, emergency lighting, design and architectural markets. To compete with and to surpass the performance of traditional lighting systems, enhancement of Lumen output and the white light quality as well as the thermal management and the luminary integration are key factors for success. Regarding these issues, white LEDs based on the chip-on-board (COB) technology show pronounced advantages. State-of-the-art LEDs exploiting this technology are now ready to enter the general lighting segments. We introduce and discuss the specific properties of the Tridonic COB technology dedicated for general lighting. This technology, in combination with a comprehensive set of tools to improve and to enhance the Lumen output and the white light quality, including optical simulation, is the scaffolding for the application of white LEDs in emerging areas, for which an outlook will be given.
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