Tachistoscopes allow brief visual stimulation delivery, which is crucial for experiments in which subliminal presentation is required. Up to now, tachistoscopes have had shortcomings with respect to timing accuracy, reliability, and flexibility of use. Here, we present a new and inexpensive two-channel tachistoscope that allows for exposure durations in the submillisecond range with an extremely high timing accuracy. The tachistoscope consists of two standard liquid-crystal display (LCD) monitors of the light-emitting diode (LED) backlight type, a semipermeable mirror, a mounting rack, and an experimental personal computer (PC). The monitors have been modified to provide external access to the LED backlights, which are controlled by the PC via the standard parallel port. Photodiode measurements confirmed reliable operation of the tachistoscope and revealed switching times of 3 μs. Our method may also be of great advantage in single-monitor setups, in which it allows for manipulating the stimulus timing with submillisecond precision in many experimental situations. Where this is not applicable, the monitor can be operated in standard mode by disabling the external backlight control instantaneously.
- IEEE transactions on image processing : a publication of the IEEE Signal Processing Society
- Published about 8 years ago
Light emitting diode (LED)-backlit liquid crystal displays (LCDs) hold the promise of improving image quality while reducing the energy consumption with signal-dependent local dimming. However, most existing local dimming algorithms are mostly motivated by simple implementation, and they often lack concern for visual quality. To fully realize the potential of LED-backlit LCDs and reduce the artifacts that often occur in current systems, we propose a novel local dimming technique that can achieve the theoretical highest fidelity of intensity reproduction in either l(1) or l(2) metrics. Both the exact and fast approximate versions of the optimal local dimming algorithm are proposed. Simulation results demonstrate superior performances of the proposed algorithm in terms of visual quality and power consumption.
Pure green light emitting diodes (LEDs) are essential to realize an ultra-wide color gamut in the next-generation displays, as is defined by the Rec. 2020 standard. However, because the human eye is more sensitive to the green spectral region, it is not yet possible to achieve an ultra-pure green electroluminescence (EL) with sufficiently narrow bandwidth that covers >95% of the Rec. 2020 standard in the CIE 1931 color space. Here, we demonstrate efficient, ultra-pure green EL based on the colloidal two-dimensional (2D) formamidinium lead bromide (FAPbBr3) hybrid perovskites. Through the dielectric-quantum-well (DQW) engineering, the quantum-confined 2D FAPbBr3 perovskites exhibit a high exciton binding energy of 162 meV, resulting in a high photoluminescence quantum yield (PLQY) of ~92% in the spin-coated films. Our optimized LED devices show a maximum current efficiency (ηCE) of 13.02 cd A-1 and the CIE 1931 color coordinates of (0.168, 0.773). The color gamut covers 97% and 99% of the Rec. 2020 standard in the CIE 1931 and the CIE 1976 color space, respectively, representing the “greenest” LEDs ever reported. Moreover, the device shows only a ~ 10% roll-off in ηCE (11.3 cd A-1) at 1000 cd m-2. We further demonstrate large-area (3 cm2) and ultra-flexible (bending radius of 2 mm) LEDs based on the 2D perovskites.
A new type of visual display for presentation of a visual stimulus with high quality was assessed. The characteristics of an organic light-emitting diode (OLED) display (Sony PVM-2541, 24.5 in.; Sony Corporation, Tokyo, Japan) were measured in detail from the viewpoint of its applicability to visual psychophysics. We found the new display to be superior to other display types in terms of spatial uniformity, color gamut, and contrast ratio. Changes in the intensity of luminance were sharper on the OLED display than those on a liquid crystal display. Therefore, such OLED displays could replace conventional cathode ray tube displays in vision research for high quality stimulus presentation. Benefits of using OLED displays in vision research were especially apparent in the fields of low-level vision, where precise control and description of the stimulus are needed, e.g., in mesopic or scotopic vision, color vision, and motion perception.
Semiconductor quantum dots (QDs) have attracted extensive attention due to their remarkable optical and electrical characteristics. While the practical application of quantum dots and further the quantum dot composite films have greatly been hindered mainly owing to their essential drawbacks of extreme unstability under the oxygen and water environments. Herein, one simple method has been employed to enhance enormously the stability of CdxZn1-xSeyS1-y quantum dot composite film by a combination of CdxZn1-xSeyS1-y quantum dots and particular polyvinylidene Fluoride (PVDF), which is characteristic of closely arranged molecular chains and strong hydrogen bonds. There are many particular advantages in the quantum dot/PVDF composite films such as easy process, low cost, large area fabrication, and especially extreme stability even in the boiling water for more than 240 minutes. By employing the K2SiF6:Mn4+ as red phosphor, a prototype white LED with a color coordinates of (0.3307, 0.3387), Tc of 5568K, color gamut 112.1NTSC(1931)% at 20mA has been fabricated, and there is little variation under different excitation currents, indicating that the quantum dot/PVDF composite films fabricated by this simple blade-coating process make them ideal candidates for LCD backlight utilization via assembling white LED on a large scale owing to its ultra-high stability under the severe environment.
Despite the excellent optical features of fully inorganic cesium lead halide (CsPbX3) perovskite quantum dots (PeQDs), their unstable nature has limited their use in various optoelectronic devices. To mitigate the instability issues of PeQDs, we demonstrate the roles of dual-silicon nitride and silicon oxide ligands of the polysilazane (PSZ) inorganic polymer to passivate the surface defects and form a barrier layer coated onto green CsPbBr3QDs to maintain the high photoluminescence quantum yield (PLQY) and improve the environmental stability. The mixed SiNx/SiNxOy/SiOypassivated and encapsulated CsPbBr3/PSZ core/shell composite can be prepared by a simple hydrolysis reaction involving the addition of adding PSZ as a precursor and a slight amount of water into a colloidal CsPbBr3QD solution. The degree of the moisture-induced hydrolysis reaction of PSZ can affect the compositional ratio of SiNx, SiNxOy, and SiOyliganded to the surfaces of the CsPbBr3QDs to optimize the PLQY and the stability of CsPbBr3/PSZ core/shell composite, which shows a high PLQY (~81.7%) with improved thermal, photo, air, and humidity stability as well under coarse conditions where the performance of CsPbBr3QDs typically deteriorate. To evaluate the suitability of the application of the CsPbBr3/PSZ powder to down-converted white-light-emitting diodes (DC-WLEDs) as the backlight of a liquid crystal display (LCD), we fabricated an on-package type of tri-color-WLED by mixing the as-synthesized green CsPbBr3/PSZ composite powder with red K2SiF6:Mn4+phosphor powder and a polymethylmethacrylate-encapsulating binder and coating this mixed paste onto a cup-type blue LED. The fabricated WLED show high luminous efficacy of 138.6 lm/W (EQE = 51.4%) and a wide color gamut of 128% and 111% without and with color filters, respectively, at a correlated color temperature of 6762 K.
This paper proposes a wide color gamut approach that uses white and emerald lighting units as the backlight of the liquid crystal display. The white and emerald backlights are controlled by the image to be displayed. The mixing ratio of the white and the emerald lighting is analyzed so that the maximal color gamut coverage ratio can be achieved. Experimental results prove the effectiveness of the wide color gamut approach using white and emerald backlights.
We present a backlight module (BLM) employing a photoluminescent quantum-dot microstructure array for flexible/curved liquid crystal displays (LCDs). Differently sized quantum-dot (QD) BLMs were prepared based on the theoretical spectral model and microstructure fabrication process. A 27-inch curved prototype showed a wide color gamut of 122.79% under the National Television Systems Committee standard while achieving high brightness of over 4000 cd/m2 and brightness/color uniformity of 85.21%/9.2 × 10-3. An LCD monitor prototype equipped with the proposed BLM was also assembled and tested, which showed higher visual performance when compared with a common commercial monitor. This method produces QD BLMs without the need of additional optical elements, and has good compatibility with traditional processes.
A phosphor-in-glass (PiG) with red and green phosphors using Nd-doped glass as a host matrix was fabricated to produce a white light emitting diode (wLED) with a wide color gamut. The Lu3Al5O12:Ce3+and CaAlSiN3:Eu2+contents were adjusted to achieve white emission for liquid crystal display (LCD) applications. The silicate glass was doped with varying concentrations of Nd2O3to modify the photoluminescence spectra of the wLED, by the hypersensitive absorption of the Nd3+:I9/24→G5/24,G27/2transition. The color coordination, the color rendering index, and the color co-related temperature of the PiG-mounted LEDs were modified by the introduction of Nd3+. The color gamut of the wLED was monitored and found to have effectively improved with the Nd3+-doped silicate glass.
A new light lab facility has been commissioned at Rochester Institute of Technology with the research goal of studying human visual adaptation under temporally dynamic lighting. The lab uses five-channel LED luminaires with 16 bits of addressable depth per channel, addressed via DMX. Based on spectral measurements, a very accurate multi-primary additive color model has been built that can be used to provide “colorimetric plus” multi-primary channel intensity solutions optimized for spectral accuracy, color fidelity, color gamut, or other attributes. Several spectral tuning and multi-primary solutions are compared, for which accuracy results and IES TM-30-15 color rendition measures are shown.