Robert Peter Scholl

A new kind of light‐generation mechanism: Incandescent radiation from clusters

A novel technique to generate hot refractory metal clusters is explained. A regenerative chemical cycle is used to form small clusters inside a microwave‐excited high‐pressure discharge which heats the clusters to 4700 K (rhenium) or 3800 K (tungsten). The discharge’s emission spectrum exhibits a strong continuum, which is the incandescent radiation of clusters. The spectral shapes of the continua and the positions of their maxima (Re: 550 nm; W: 700 nm) are characteristic of the refractory metal. A first theoretical description of the clusters’ radiation can be based on the Mie theory. Measurements of emission and absorption coefficients are performed to determine the optical properties and temperatures of the clusters. The existence of clusters with an average size of about 2.5 nm is proved by a laser scattering experiment. The properties of the cluster radiation, especially the continuous spectrum and the high luminous efficiency, are attractive for lighting applications.

Revealing the neural response to imperceptible peripheral flicker with machine learning

Lighting in modern-day devices is often discrete. The sharp onsets and offsets of light are known to induce a steady-state visually evoked potential (SSVEP) in the electroencephalogram (EEG) at low frequencies. However, it is not well-known how the brain processes visual flicker at the threshold of conscious perception and beyond. To shed more light on this, we ran an EEG study in which we asked participants (N=6) to discriminate on a behavioral level between visual stimuli in which they perceived flicker and those that they perceived as constant wave light. We found that high frequency flicker which is not perceived consciously anymore still elicits a neural response in the corresponding frequency band of EEG, con-tralateral to the stimulated hemifield. The main contribution of this paper is to show the benefit of machine learning techniques for investigating this effect of subconscious processing: Common Spatial Pattern (CSP) filtering in combination with classification based on Linear Discriminant Analysis (LDA) could be used to reveal the effect for additional participants and stimuli, with high statistical significance. We conclude that machine learning techniques are a valuable extension of conventional neurophysiological analysis that can substantially boost the sensitivity to subconscious effects, such as the processing of imperceptible flicker.

Low-pressure indium-halide discharges for fluorescent illumination applications

Low-pressure gas discharges of molecular radiators were studied for fluorescent lighting applications with a goal of reducing the energy loss due to the large Stokes shift in phosphors of conventional mercury-based fluorescent lamp technology. Indium halides (InCl, InBr, and InI) were chosen as the molecular radiators that generate ultraviolet to blue light emissions. The electrical characteristics and optical emission intensities were measured in discharges containing gaseous indium halides (InCl, InBr, and InI) as molecular radiators. The low-pressure discharges in indium halide vapor showed potential as a highly efficient gas discharge system for fluorescent lighting application.

Cluster lamp‐a new kind of light generation mechanism

Investigations on a new type of light generation mechanism have led to the development of the so called cluster lamp. Their operation is based on the regenerative formation and heating of small metal particles (clusters) in a microwave excited high intensity discharge. These lamps combine the excellent colour quality of incandescent lamps with the high efficiency of discharge lamps. Depending on the used filling, lamps with different colour temperatures for different application areas can be made.

Incandescent Radiation from 3500 K Hot Clusters

Hot refractory metal clusters have been produced by a novel experimental technique. A regenerative chemical cycle established in a high pressure microwave tungstenoxyhalide or rheniumoxide discharge leads to condensation of nanometer size tungsten or rhenium clusters with a mean temperature of about 3500 K or 4500 K, respectively. The clusters emit incandescent radiation with broad continuous spectra. The spectral shapes of the continua and the positions of their maxima (W 700 nm, Re 550 nm) are characteristic for the refractory metal. A first theoretical description of the clusters’ radiation can be based on the Mie theory. The existence of clusters with spherical shape and a mean size of about 2 nanometers has been proven by a laser scattering experiment. The properties of the cluster radiation especially the continuous spectrum and the high luminous efficiency are attractive for lighting applications.

A New Generation of Highly Efficient Light Sources

In the last 5 years a close co-operation between the Bonn-Rhein-Sieg University of Applied Sciences and the Philips Research Laboratories in Aachen has been established. In this article I want to report on the co-operation of the Department of Electrical Engineering, Mechanical Engineering and Technical Journalism with Philips. Besides a number of diploma theses on the field of water treatment with new discharge lamps, power electronics and modelling of electromagnetic field configurations, there is running also an activity on a new generation of highly efficient light sources based on molecular discharges.