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Projection systems have found widespread use in conference rooms and other professional applications during the last decade and are now entering the home TV market at a considerable pace. Projectors as small as about one litre are able to deliver several thousand screen lumens and are, with a system efficacy of over 10 lm W-1, the most efficient di...
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... projectors-now commonly called 'beamers'-have found their place in almost each meeting room during the last ten years. In the last few years also, rear projection TV sets (see figure 3) have become important in the market and sales are growing rapidly. Short arc lamps are a key component for projection systems for achieving the highest efficiency for small projection display sizes. ...
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... trend in the field of digital data projection is the drastic reduction in projector size seen since the introduction of the UHP lamp. From figure 30 one can see that the lamp and driver volume has shrunk to 1/10 of its original size since 1996. In the same time frame, the volume of an average projector has reduced to one-third. ...
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... to the sharp edges of the foil, relatively low voltage is sufficient to extract electrons and create a breakdown within the UV enhancer. Subsequently, a capacitive discharge between the foil and the antenna produces UV light, which is conducted along the sealing by total internal reflection towards the main burner cavity, see figure 34. There the UV photons create electrons by photo-emission and a primary breakdown in the main cavity is induced. ...
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... metal wire close to the burner can modify the field distribution inside the burner and helps to lower the required restrike voltage. The field forming wire can be combined with the antenna around the UV enhancer, as indicated in figure 33. ...
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... figure 35 measurements of the required ignition voltage over time after switch-off are shown for different ignition aids. With the application of the antenna wire, the lamp can be ignited with voltages as low as 5 kV, after 50 s, which is a clear improvement compared with the standard situation without ignition aids. ...
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... the application of the antenna wire, the lamp can be ignited with voltages as low as 5 kV, after 50 s, which is a clear improvement compared with the standard situation without ignition aids. The measurement in figure 35 has been done without any cooling. If the projector provides lamp cooling after switch-off, the re-ignition times can be reduced further. ...
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... parabolic reflector shapes are preferred in combination with lens array optical integrators, while elliptical reflectors are ideally suited for combination with rod-type integrators. Figure 36 shows the size evolution of Philips UHP reflector lamps over the last few years. Several design considerations led to the reflector size reduction. ...
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... reflector has to cover as much as possible of this solid angle. Rays that do not hit the reflector are lost and generate heat in the system (red ray in figure 37). ...
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... design criterion for elliptical reflectors is the total length of the optical path. For compact projectors, where a major contribution is the distance between the first and the second focus d f 1f 2 (see figure 37), this length should be minimized. ...
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... finally, it should be ensured, that the burner is not unnecessarily heated by light that hits the front end of the burner. Both, light beams coming directly from the reflector and beams that are reflected back from filters or optics placed in the beam path, contribute to a heating of this already critical region of the burner (purple rays in figure 37). ...
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... smaller reflector sizes are made possible by an integrated reflector concept. By applying a dichroic coating on one hemisphere of a UHP burner ( figure 38) the visible part of the spectrum is reflected while the major parts of UV and IR are transmitted. Because the outer shape of the UHP burner is a perfect sphere the light is reflected back through the arc towards the uncoated side of the burner. ...
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... special dichroic coating successfully developed by Philips (see figure 39) survives the extreme thermal conditions on the UHP burner without damage for thousands of hours. The first products described below have a guaranteed life of 2000 h. ...
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... a set-up using a UHP burner (without its standard reflector) and a separate spherical mirror, where the burner is positioned exactly in the centre point of the spherical reflector, it is possible to adjust the reflected light such that it is superposed to the original arc. The spectra of the UHP lamp with and without this retro-reflection are shown in figure 43. The green curve shows the spectrum from the burner without the additional retro-reflection, whereas the red curve is obtained by using the spherical mirror. ...
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... Spectral needs come in a different flavor; instead of a good color rendering, a lot of light in some primary color regions is required. In the late 1990s, microdisplay technology imager technology including liquid crystal display (LCD), digital light processing (DLP) 18 , liquid crystal on silicon (LCOS), and ultra-high pressure mercury (UHP)type lamps 19 came almost simultaneously to maturity, causing a steep rise of the projection market. After 2010, laser-phosphor-based projectors 20, 21 entered the market, and a few years later, LED projectors passed the 1000 ANSI lm threshold thanks to thin film LED technology and higher étendue imagers [22][23][24] . ...
... The results range from 30 to 400 µm 2 · sr, decreasing with increasing n. These numbers are much lower than the etendue of typical projection systems using liquid-crystal display (LCD), digital light projection (DLP) and LED based luminescent concentration techniques, which are around 8 to 25 mm 2 · sr [36,37]. The low etendue arises from the combination of a small emission angular range, and the micron size of arrays. ...
In this work, we study plasmon antenna array lasers for solid-state lighting (SSL). Optically pumped plasmon antenna array lasers can provide benefits suitable for SSL including efficient pump-light absorption, high brightness, and good directivity. However, applying lasers in SSL is difficult because of speckle formation. To overcome this issue, we propose two types of lasers based on patchworks of small plasmon lattices with different lattice constants, tessellating an extended surface. The premise is that they could ultimately form a blue-LED pumped broad-area directional emitter with reduced coherence to suppress speckle. An important question is whether different patches couple when assembled together, and how this affects spatial and spectral profiles. In this paper, we show measurement results on the plasmon patchwork lasers, and discuss their modelling and potential application as low etendue and speckle free sources in SSL.
... Single spectral lines containing a high UV-part below 380 nm are visible. No continuum is present in the spectrum ( [103]). At 200 W about 50% of the nominal operation power are coupled into the lamp. ...
This thesis presents the analysis of microwave plasma frequency-dependence based on the investigation of multi-physical parameters.
Fundamentals of a microwave plasma and high-frequency technology are explained. Frequency-dependent effects on the base point impedance are presented in combination with the description of the used measuring hardware.
Development of a bi-static network for the main plasma states (ignition and operation) is presented on the example of two high-pressure lamps at 2.45 GHz. Networks of both lamps are custom-built during the course of this thesis. An efficacy of 135 lm/W is achieved exceeding the efficacy of most LEDs.
Frequency-dependent electrical properties are analyzed by reflection measurements of three different prototypes (argon plasma jet, phosphor-coated lamp and hollow glass cylinder filled with xenon) for the first time. A novel and simple lumped element and 3D-model are developed for the fitting of the plasma. A series resonance circuit substitutes the frequency-dependency of the capacitive plasma. The models are extended for S21 measurements by a novel developed transmission prototype. A simple frequency-dependent capacitor lumped element model fits the transmission parameters of the plasma. The novel core/cone3D-model is capable of fitting the plasma in an FEM simulator by only using the conductivity.
A significant influence of the frequency on the spatial properties of all prototypes is measured for the first time by a simple CMOS camera and a custom image registration routine. The spatial extension is inversely proportional to the frequency. Optical measurements identify the participating ion species. Influence of the frequency on single spectral bands are presented in an in-depth analysis using optical emission spectroscopy. A proportionality of the frequency and the energy density in the microwave plasma is revealed. This is supported by the thermal measurements. The plasma jet rotational temperature is determined by the hydroxyl band at 310nm and shows a maximum values of 1350 K at only 15 W.
... There are a few applications, however, where gas-discharge lamps, like UHP and Xenon lamps, are still superior. Especially arc lamps can provide a small source with high brightness and are used in applications like digital projection [1], automotive lighting and special spot lights, e.g. for arena lighting. The main drawbacks of these lamps are a short life time, the use of mercury (in some cases) and limited lumen maintenance over life-time (ageing) as well as catastrophic failure. ...
The concept of a high-luminance light source based on luminescent conversion of LED light and optical concentration in a transparent phosphor is explained. Experiments on a realized light source show that a luminous flux of 8500 lm and a luminance of 500 cd/mm² can be attained using 56 pump LEDs at 330 W electrical input power. The measurement results are compared to optical simulations, showing that the experimental optical efficiency is slightly lower than expected. The present status enables applications like mid-segment digital projection using LED technology, whereas the concept is scalable to higher fluxes.
... UV enhancers are also well-established ignition aids in HID lamps for video projecting systems, e.g. UHP lamps [23]. For automotive HID lamps an outer-bulb discharge is often used as ignition aid [1,[4][5][6][7]. ...
This paper considers the ignition of mercury-free high-intensity discharge (HID) lamps for car headlights. Due to safety reasons, these lamps need to have a fast run-up phase which is ensured, amongst other things, by a high Xe pressure of roughly 15?bar (cold) in the discharge vessel. The high Xe pressure causes an increased ignition voltage compared with former mercury-containing automotive HID lamps or low-pressure lamps used for general-lighting applications.
The increase in ignition voltage can be limited if the electric field in front of the electrodes is raised by an uplifting of the electrical conductivity along the outer wall of the inner bulb either by a conductive layer on its surface or by a dielectric barrier discharge (DBD) within the outer bulb. This paper considers on the one hand conventional antennas deposited by physical vapour deposition (PVD) and on the other hand a combination of these antennas with a DBD within the outer-bulb operated in 100?mbar Ar as ignition aids. In both cases the antenna potential and antenna width are varied. Additionally, the effects of antenna thickness and antenna material are investigated.
The ignition voltage, ignition current and light emission during ignition are measured on a nanosecond timescale. Furthermore, for the very first time, the ignition process is recorded in four consecutive intensified charge-coupled device images using a high-speed camera system with a time resolution in the range of nanoseconds.
It was found that antennas strongly reduce the ignition voltage of automotive HID lamps. Active antennas reduce the ignition voltage significantly more than passive antennas, proportional to the conductance of the antenna. Combining conventional antennas with an outer-bulb discharge reduces the ignition voltage from 19?kV without any ignition aid to the intrinsic ignition voltage of the lamp below 10?kV, in the best case.
... Another source of radiation in a high pressure discharge could be the 'molecular radiation' that is emitted by excimers, which is a primary source of radiation in UHP discharge lamps at p 200 bar [23]. However, the excimers are created in three-body collisions of excited states with atoms in a ground state, thus their density should be roughly proportional to the square of pressure. ...
Energy losses due to radiation in an LTE arc plasma in argon are investigated in the temperature range from 5000 to 15 000 K. Calculations of the radiation transport require us to know the absorption spectra; for that purpose, free–free, bound–free and bound–bound transitions are taken into account. The energy losses due to resonance transitions with large absorption coefficients are analyzed. The transport of visible radiation with small absorption coefficients is calculated by accurate integration over a whole spectrum. The resonance radiation transport in LTE plasma is described by the Biberman–Holstein equation, which is usually used in non-equilibrium plasma. As the temperature grows, radiation processes become the main channel of energy losses. It is shown that, despite the resonance radiation being trapped, the energy losses due to resonance radiation escape can achieve 10% of the total radiation losses.
... It was expected that the larger diameter of 8 mm required higher input power for ignition due to higher dielectric losses of the glass and due to the higher distance from the inner coaxial line to the burner [6]. Therefore the larger diameter was chosen for simulation so both lamps could be ignited and operated using the same matching network. ...
... Visible in the spectrum are single lines containing a high UV-part below 380 nm. Since the lamp is built for higher power levels in the 400 W-area and driven at about 50 % of its normal operation power no continuum is present in the spectrum [6]. This is due to a lower than nominal pressure inside the burner. ...
High-intensity discharge lamps can be driven by radio-frequency signals in the ISM frequency band at 2.45 GHz, using a matching network to transform the impedance of the plasma to the source impedance. To achieve an optimal operating condition, a good characterization of the lamp in terms of radio frequency equivalent circuits under operating conditions is necessary, enabling the design of an efficient matching network. This paper presents the characterization technique for such lamps and presents the design of the required matching network. For the characterization, a high-intensity discharge lamp was driven by a monofrequent large signal at 2.45 GHz, whereas a frequency sweep over 300 MHz was performed across this signal to measure so-called small-signal hot ${S}$-parameters using a vector network analyzer. These parameters are then used as an equivalent load in a circuit simulator to design an appropriate matching network. Using the measured data as a black-box model in the simulation results in a quick and efficient method to simulate and design efficient matching networks in spite of the complex plasma behavior. Furthermore, photometric analysis of high-intensity discharge lamps are carried out, comparing microwave operation to conventional operation.
... This ignition aid is widely used in HID lamps for video projecting systems, e.g. UHP lamps [21]. A UV enhancer is a small volume in the vicinity of the pinch filled with a noble gas atmosphere and sometimes with mercury [21]. ...
... UHP lamps [21]. A UV enhancer is a small volume in the vicinity of the pinch filled with a noble gas atmosphere and sometimes with mercury [21]. By applying the ignition voltage a capacitive glow discharge in the UV enhancer is ignited and produces UV photons. ...
... The UV radiation of the deuterium lamp is able to enter the inner bulb where it produces free electrons by the photo-electric effect similar to a UV enhancer [21]. Photons with a wavelength of λ 270 nm are required to release photo-electrons at the tungsten electrodes with an average work function φ = 4.5 eV. ...
This work considers the ignition process of mercury-free high-intensity discharge lamps used for car headlights. These lamps have to run-up fast. This is achieved with a high xenon pressure of about 15 bar (cold) in the inner bulb. The high filling-gas pressure causes an increased ignition voltage compared with lower-pressure lamps used in general-lighting applications.
In this paper the possibility is investigated to reduce the ignition voltage by optimizing a dielectric-barrier discharge (DBD) in the outer bulb working as ignition aid. A special outer bulb was built up allowing gas exchange and adjustment of the gas pressure. For diagnostic purposes different electrical and optical methods are used, namely the recording of ignition voltage, ignition current and light emission by a photo-diode signal on nanosecond time scale as well as short-time photography by a intensified charge-coupled device camera.
It was found that the DBD mainly generates a potential distribution within the lamp which supports ignition by an increase in the E-field in front of the electrodes and the wall. It is shown that this effect is distinctly more effective than UV radiation potentially emitted by the DBD.
... Discharge lamps containing mercury at pressures greater than 100 bar (referred to as VHP-Hg discharges) are used commercially in data projectors and television projection systems, because they produce extremely bright 'white' light [1]. Typically, the discharge is contained in a very thick-walled burner of fused silica with an arc gap of around 1 mm. ...
... As noted by Wharmby [2], molecular absorption, bremsstrahlung and atomic radiation play an important role in very high-pressure lamps. All these phenomena have been included in the calculation of the local absorption coefficient to solve equation (1) in the ray-tracing model, and the results are in good agreement with the spectra measured by Wharmby in his experiments. As an illustration, figure 7 shows the comparison of the model with the experimental measurements for the Hg 365 nm spectral line. ...
... Since all the lamps studied have the same dimensions, the ray-tracing model is performed once only, and it is used by the three discharges described in table 2. We first describe the results from the dc discharge and then compare them with results from the two mw discharges. Figure 8 shows the side-on intensity of two spectral lines for the dc discharge, compared with the experimental measurements obtained from optical emission spectroscopy [1,2]. ...
Discharge lamps containing mercury at pressures above 100 bar are
commercially used in data projectors and television projector systems.
Due to their small size, these lamps are difficult to investigate
experimentally, but spectral measurements, combined with radiation
transport calculations, have provided useful information on the visible
spectrum. However, classical spectral line broadening theory is
inadequate to describe the UV portion of the spectrum, so
self-consistent modelling of these discharges is not possible at
present. This paper discusses the differences between discharges
containing electrodes and discharges sustained by a microwave (mw)
electromagnetic field, on the basis of the experimentally measured
temperature profile in an electroded discharge, and a temperature
profile computed from a 1D power balance model for a microwave
discharge. A model based on the ray-tracing method is employed to
simulate the radiation transport in these lamps. The model has been
validated by comparing the emission spectrum from dc discharge lamps
with those obtained experimentally. The output flux, luminous flux,
luminous efficacy, the correlated colour temperature, the chromaticity
coordinates and photometric curves of the lamp were then obtained. These
results were also compared with those of a theoretically calculated
temperature profile for the same lamp, excited by microwave power in the
TM010 mode.
... To apply optical absorption spectroscopy a powerful broadband ultra-high performance (UHP) lamp [30] (Philips 228 L4) is positioned behind the YAG lamp on the elongation of the optical axis. This backlight exhibits a high radiance within the visible spectral range and a temporarily very stable emission. ...
Presently, most high intensity discharge (HID) lamps contain mercury to generate a high pressure buffer gas and thereby an appropriate power input into the arc. Due to its toxicity, the replacement of Hg is of particular interest in recent research on HID lamps. Up to now, the emission coefficient of an atomic Hg double line is widely used to determine the plasma temperature Tpl in HID lamps. Tpl is needed to calculate the total density of atoms and ions of elements inside these lamps. A combination of optical emission and broadband absorption spectroscopy allows us to evaluate Tpl independently of Hg emission lines. The method is required for a determination of Tpl if the Hg line intensity within the investigated lamp is too low, is superimposed by other lines or if environmental-friendly Hg-free lamps are developed.
Within this work, phase-resolved plasma temperatures are determined in front of the electrode of Hg-containing MH lamps by emission spectroscopy at atomic Hg lines. Above all, temperatures are measured by a combination of emission and absorption spectroscopy at atomic rare earth lines, namely Dy and Tm. A comparison of Tpl determined by both methods agree within an error margin of <10%. Total phase-resolved rare earth atom densities are obtained by means of the measured ground state densities and Tpl. The combination of emission and absorption spectroscopy is also applied to the bulk plasma of lamps where the intensity of the Hg emission lines is too low for plasma temperature measurements or Hg is absent. It provides the partial rare earth pressure and by comparison with thermodynamic data cold spot temperatures within the lamps.
