Rigid endoscopes are optical systems characterized by high light losses and poor light transfer efficiencies below 20 %. We investigated this issue first by performing a photometric analysis of three state of the art endoscopes and second by carrying out an optical analysis by means of an optomechanical model with the optical design software LightTools (Synopsys). The light losses in the material and the critical interfaces of the optomechanical model are then analyzed by considering both the spectral power distribution of the light source and the light distribution that is coupled into the endoscope’s illumination optics. To improve the illumination optics of rigid endoscopes three approaches are presented in this work: a compound parabolic concentrator and a fiber cone are first developed as alternative coupling elements but only a minor improvement could be realized, because the present optical system is highly constraint by étendue law. Therefore, an immersion element is secondly introduced between coupling element and fiberbundle to reduce backscattering between the interfaces and to increase the overall light transfer efficiency. However, it turned out that a 10 % increased light transfer efficiency can be achieved only by selecting high numerical aperture fibers combined with the immersion element. Third, the influence of the initial coupling element’s geometry on the light distribution in the surgical field is investigated. The optical simulations show that by lengthening the coupling element’s truncated cone the light can be distributed more uniformly in the surgical field.
The rapid improvement of the LED-efficiency in the visible range and the availability of UVA-LEDs motivated us to
perform a feasibility study focused on developing a light module powered only with LED sources for photostability tests
in constant climate chambers. We first carried out a market analysis to identify suitable LEDs for this application.
Secondly, a new opto-mechanical light module was developed and optically simulated with the software LightTools®.
The geometrical distribution of all LEDs was optimized to provide uniform illumination at a given distance and
a spectral distribution according to the guideline ICHQ1b for photostability tests. Finally, an opto-mechanical prototype
was built up and measured. Both irradiance/illuminance measured values and spectral distribution were in very good
agreement with the optical simulation values. The uniformity too was better than predicted and within the 10% target
value. Nevertheless, in a further optimization, a 3D-textures pattern was added on the front size of the glass plate located
under the LEDs. According to the final optical simulation results this typical backlighting optimization provides an
additional improvement of the uniformity. In conclusion, we have demonstrated that LEDs can already provide an
efficient optical alternative to classical fluorescent lamps in this demanding industrial application field. But two few
UVA-LEDs with the right wavelength and power are available on the market. And none has undergone the reliability
tests required by this application (humidity, temperature, lifetime )
Within the framework of a project conducted together with an industrial partner, a self-disinfecting operation interface
with a glass panel is being developed. The concept of self-disinfection is based on the exploitation of the photocatalytical
effect induced by a TiO2-coating on the glass surface under UV(A) light, which would make the touch screen
antimicrobial. High-power UV-LEDs instead of conventional UV-lamps have been employed as light source.
The main goal and challenge of the optical design is to generate an efficient and preferably homogeneous UV field on
the TiO2-coated side while keeping the UV-LEDs concealed, i.e. invisible to the user. Therefore common backlighting
systems have been used as reference and modified to meet the concrete requirements. Primary analysis and optical
simulations have been performed with the software LightTools®. Several patterns for light redirection (i.e. 3D-spherical
texture, 3D-rectangular texture and 2D-circular serigraph) have been investigated, compared and evaluated. Finally the
pattern design which both fulfills all the predefined boundary conditions and simultaneously reduces the costs has been
chosen.
We developed a hollow light guide (HLG) model which allows to predict the best extractor combination for any given
HLG length and for typical constraints like mean illuminance values and uniformity. The HLG prototype we analysed
has a diameter of 30 cm, a 16 m length, 3M prismatic structures on the inner walls, curved light-reflecting surfaces with
different shapes working as light extractors. It is powered by a projector with a 400W HIT-lamp. Firstly, we
characterised extractors by their flux "consumption" and extraction. Then, we developed an analysis software to allow
real time acquisition of floor illuminance data by means of a cooled, calibrated photometric CCD camera. We thus
modeled the HLG as a lineal system of extractors. To evaluate both output flux and uniformity of the illuminance
distribution of an extensive set of solutions, we wrote a Simulation Software Extractor Position (SISEPO). SISEPO was
tested to optimise the extractor sequence of the initial HLG and a 15% improvement of the mean floor illuminance was
predicted. The corresponding measured values were in good agreement and also the measurements of the luminous
intensity distributions of the whole HLG-luminaire (EULUMDATA), carried out in individual segments of one meter
length, confirmed the improvement of the light extraction efficiency.
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