The general V(λ) mismatch index, f1′ , of a photometer quantifies the deviation between its determined relative spectral responsivity, srelλ , and its nominal responsivity, the spectral luminous efficiency function for photopic vision, V(λ). LED-based light sources now dominate in general lighting, displacing incandescent and fluorescent lamps. Furthermore, the calibration of photometers will very likely see the replacement of the reference CIE standard illuminant A with CIE reference spectrum L41. The article evaluates the consequences. Should we also change the definition of the general V(λ) mismatch index? Based on performance criteria, the individual indices are evaluated using various datasets with the help of statistical analyses. As a result, the authors can conclude that the current definition works very well even under changed calibration and application conditions and does not need to be changed. Other evaluated indices for a new index definition perform only slightly better in some cases, but do not generate generally better properties.

Imaging Luminance Measuring Device (ILMD) based luminous intensity distribution measurement systems are an established method for measuring the luminous intensity distribution (LID) of light sources in the far field. The advantage of this system is the high-resolution acquisition of a large angular range with one image. For the uncertainty budget, the mathematical description of the system can be divided into photometric and geometric contributions. In the following, we will present a Monte-Carlo approach to analyse the geometric contributions which are the uncertainty of measurement direction and measurement distance. Therefore, we set up a geometric system description based on kinematic transformations that describes the connection between detector and light source position. To consider all relevant input quantities we simulate the adjustment and measurement process. Finally, an analysis of the geometric input parameters is shown.

In this work, we present a method to describe the model of a goniophotometer for uncertainty analysis by state-of-the-art Universal Robotic Description Format (URDF). The parameters of the kinematic chain model are determined by measurements of the geometric properties of the goniophotometer. The uncertainties of the pose are determined using Monte Carlo (MC) simulations of the kinematic chain. The measured geometric uncertainties are input the MC simulations. The proposed framework enables high level description of kinematic chains for MC simulations of measurement systems. Furthermore, the uncertainty of the total system is demonstrated over the MC trials to prove a sufficient amount of MC trials. The results of this generic approach are evaluated against an existing model and the uncertainty determination of the same goniophotometer.

This work presents, summarizes and validates a fast, accurate and general measurement and modeling technique to obtain spectral near field data of LED systems in order to improve the optical design process of modern high quality LED systems. It requires only a minimum of goniophotometric near field measurements as well as no time-consuming angularly resolved spectral measurements. The procedure is named physically motivated basis spectra (PMBS) as its main assumption is that each piece of angularly and spatially varying spectral information can be described as the weighted sum of its physical basis spectra such as the individual semiconductors or a phosphor. Based on detailed spectral information regarding the goniophotometric measurement setup, the spectral model is obtained by solving a simple system of linear equations using the obtained near field measurements. The complete process is validated and applied to different state-of-the-art LED systems. The obtained results can be used directly in state-of-the-art ray tracers.

In this work, we propose a method to indirectly measure the complete angle-dependent light intensity distribution (LID) of lamps and luminaires, using a goniometer, a white screen and a luminance camera. The goniometer permits an accurate variation of two angles in spherical coordinates by moving the Device Under Test (DUT). We take several camera images of the reflexion of the DUT on the screen with different viewing angles, correct the perspective distortion of each image using planar homography and finally merge the set of images using the geometrical information of the system. We designed and measured a special DUT, which produces known LIDs and photometrical values, and compared the results with conventional scanning methods, in order to validate the proposed method and to estimate their measurement uncertainty. Using the suggested process, higher resolutions and lower measurement times can be obtained.

Precise spectral and colorimetric simulations in commercial ray tracing software require realistic light source models, which provide spectral information as a function of angle and spatial dimension. We describe and validate a general workflow to create hyperspectral LED models as a linear combination of spectral models. The workflow only requires user defined precisions and rayfiles obtained with different optical filters. The rayfiles are transformed into histogram based models, whose precision is evaluated by normalized cross-correlation values of their intensity distributions in the near-, mid- and far field. Additionally, the concept is evaluated with a spatial and spectral well defined test device.

To simulate and optimize optical designs regarding perceived color and homogeneity in commercial ray tracing software, realistic light source models are needed. Spectral rayfiles provide angular and spatial varying spectral information. We propose a spectral reconstruction method with a minimum of time consuming goniophotometric near field measurements with optical filters for the purpose of creating spectral rayfiles. Our discussion focuses on the selection of the ideal optical filter combination for any arbitrary spectrum out of a given filter set by considering measurement uncertainties with Monte Carlo simulations. We minimize the simulation time by a preselection of all filter combinations, which bases on factorial design.

Optimizing angular or spatial colour homogeneity has become an important task in many general lighting applications and first requires a valid description of illumination colour homogeneity. We analyse different frequently used methods to describe colour distributions in theory and with measurement data. It is described why information about chromaticity coordinates, correlated colour temperature and global chromaticity coordinate distances are not sufficient for describing colour homogeneity perception of light distributions. We present local chromaticity coordinate distances as expandable and easy implementable method for describing colour homogeneity distributions that is adaptable to the field of view by only one intuitive, physiological meaningful parameter.

We present a high power density UV LED module for a wavelength of 395 nm with an optical power density of 27.3 W/cm2. The module consists of 98 densely packed LED chips soldered onto an Al2O3 ceramic board. Thermal and optical measurements were conducted. The module was cooled by a forced air heat sink for the characterization experiments. A room temperature liquid gallium alloy was used as thermal interface material between substrate and heat sink with a TiN barrier layer to prevent corrosion. Further a technology to replace Al2O3 ceramics by aluminum as substrate is presented. An initial characterization shows that aluminum with a dielectric layer for electrical insulation is a competitive substrate material for efficient heat removal.

We present a high power density UV-LED module for a wavelength of 395 nm with an optical power density of 13.1 W/cm(2). The module consists of 98 densely packed LED chips adhesively bonded to an Al2O3-ceramic board. Thermal simulations and measurements as well as optical measurements were conducted. The module was cooled by a forced air heat sink for the characterization experiments. A surface micro cooler with water as a coolant is proposed to improve thermal performance of the module. To drive the LED module, we developed an efficient current source powered directly from AC mains supply with integrated power factor correction using a single switching component.

LaPO4:Ce,Tb as a nanoscale phosphor is prepared via a microwave-accelerated synthesis in ionic liquids. The underlying approach results in non-agglomerated nanocrystals, 912 nm in size, and exhibiting quantum yields of 70 % (Tb-related emission) and 90% (Ce/Tb-related emission). Based on the underlying concept of synthesis, application-oriented aspects are focused. Driven by the addition of oleylamine, first, phase transfer from the polar phase of synthesis to non-polar alkanes can be initiated. As a second aspect, dispersions of the title compound in ethanol are applied for ink-jet printing of transparent luminescent layers on polymer substrates. Finally, ethanolic dispersions of LaPO4:Ce,Tb are used to realize a fully transparent dielectric barrier discharge (DBD) lamp as a prototype of a "luminescent window". ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008).

Xe excimer DBD operate in a filamented or homogeneous mode depending on several parameters, e.g. the electrical excitation. The need of a pulsed excitation for homogenous discharge is well known from literature. However, the role of the electrical excitation to homogenize the DBD is not complete understood. In this work the transfer from filamented to homogenous mode is investigated for sub-microsecond pulses. Measurements of the gap voltage and plasma current show the influence of reignition for a homogeneous operation. The correlation between short time NIR images and current measurements point out that filamentation is depending on current density during ignition. It is shown that the filaments wide up with increasing current, like in an arc discharges. The filament expands with increasing ignition current and form a 2-dimensional pattern which goes finally over to a complete homogeneous discharge. It can be shown, that the current density through the ignited area is constant and a threshold current density for homogenous discharges can be defined depending on the strength of reignition and Xe pressure. The constant current density in the ignited area explains the transition from filamented to homogenous mode. This shows that current during ignition is the critical electrical parameter and not the rise time of the lamp voltage. To display the dependency of threshold current density and reignition, sub-microsecond pulses with a negative lamp voltage undershoot are shown. The threshold current lowers with increasing reignition. This behavior could be explained with accumulated remaining charges on the barriers from the last excitation pulse. Based on the need of a high current during ignition a novel DBD pulse gear with enforced reignition is presented with good system efficiency.

In a DBD it is not possible to measure the electrical values of the plasma directly. To determine them it is necessary to separate the capacitive from the real current component within the gap. To overcome this problem Liu and Neiger have published an analytical method to determining the plasma values from the lamp voltage and current. This method is very complex and needs some simplification to differentiate and integrate the voltage and current values over time so that a real time analysis is not possible. Based on this model, Roth and Schwarz developed an electrical setup to measure the inner values directly. We have developed this method further and have now the possibility to determine the plasma voltage, current for pulsed operation. Based on this measurement method we have developed an electrical model to describe the role of space charges inside the gap. With the model it is possible to amount the electrical field of space charges integrated as voltage ucharge. The difference between the determined voltage ucharge and the measured gap voltage describes the effective exciting voltage uexcite. Examples of sinusoidal and pulsed excitation show that this model could describe the development of space charges correctly. The new defined ignition voltage uexcite,max shows, despite the old definition of ugap,max, no dependence on the voltage waveform and describes the behavior of preionization correctly.