The feasibility of applying ultraviolet light-emitting diodes (UV-LED’s) as triggering sources of photo-catalyst based on titanium dioxide (TiO2) nano-coating specifically for water-cleaning process in an aquaponics system was designed and proposed. The aquaponics system is a modern farming system to integrate aquaculture and hydroponics into a single system to establish an environmental-friendly and lower-cost method for farming fish and vegetable all together in urban area. Water treatment in an aquaponics system is crucial to avoid mutual contamination. we proposed a modularized watercleaning device composed of all commercially available components and parts to eliminate organic contaminants by using UV-LED’s for TiO2 photo-catalyst reaction. This water-cleaning module consisted of two coaxial hollowed cylindrical pipes can be submerged completely in water for water treatment and cooling UV-LED’s. The temperature of the UV-LED after proper thermal management can be reduced about 16% to maintain the optimal operation condition. Our preliminary experimental result by using Methylene Blue solution to simulate organic contaminants indicated that TiO2 photo-catalyst triggered by UV-LED’s can effectively decompose organic compound and decolor Methylene Blue solution.
The distinguishable and non-distinguishable 6-bit (64) grayscales of green and red organic light-emitting diode (OLED) were experimentally investigated by using high-sensitive photometric instrument. The feasibility of combining external detection system for quality engineering to compensate the grayscale loss based on preset grayscale tables was also investigated by SPICE simulation. The degradation loss of OLED deeply affects image quality as grayscales become inaccurate. The distinguishable grayscales are indicated as those brightness differences and corresponding current increments are differentiable by instrument. The grayscales of OLED in 8-bit (256) or higher may become nondistinguishable as current or voltage increments are in the same order of noise level in circuitry. The distinguishable grayscale tables for individual red, green, blue, and white colors can be experimentally established as preset reference for quality engineering (QE) in which the degradation loss is compensated by corresponding grayscale numbers shown in preset table. The degradation loss of each OLED colors is quantifiable by comparing voltage increments to those in preset grayscale table if precise voltage increments are detectable during operation. The QE of AMOLED can be accomplished by applying updated grayscale tables. Our preliminary simulation result revealed that it is feasible to quantify degradation loss in terms of grayscale numbers by using external detector circuitry.
The feasibility of applying a five-inch diagonal white organic light-emitting diode (WOLED) as a desk lamp was experimentally investigated by quantitatively comparing its two-dimensional (2D) optical intensity profile to that of a traditional 3M desk lamp equipped with optical diffuser. The 2D optical distribution patterns as the function of vertical distances to a surface of a five-inch diagonal WOLED were obtained by using rapid rotating measurement technique consisted of a sample holder on a rotational stage and a fixed photo detector with optical power meter. The 2D optical intensity profile on a surface can be rapidly established in a relatively small space by recording the reading from the fixed photo detector as rotating the sample holder. This rapid measurement technique is suitable for practical application in quality engineering without larger space. A WOLED is a compact and thin lighting source with planar device structure without additional optical components. Its optical intensity profile on a plane is expected to be different from traditional lighting sources. The optical distribution pattern of a desk lamp requires a relatively large area on a surface with relatively uniformed intensity distribution. The quantitative analysis of the similarity between WOLED and 3M desk lamp was conducted by comparing the optimal zones defined as the area within 75% of the maximum intensity in 2D optical distribution pattern. Our preliminary result showed that the optimal zone of a five-inch diagonal WOLED at 45cm vertical distance is highly similar to that of the 3M desk lamp with optical diffuser.
A statistical distribution function capable of numerically characterizing the unique intensity distribution of a planar white organic light-emitting diodes (WOLED) was theoretically investigated by fitting our experimental data obtained by microscopic goniometer (MG) system associated with an energy analyzer to the normal distribution function with amplitude, average, and standard deviation as adjustable parameters. The WOLED is one of the upcoming lighting sources with planar device structure without additional optical components. The intensity characteristic of a lighting source is crucial for practical purpose. The procedure of an optical design usually requires proper numerical tools to satisfy specific application by adjusting parameters. Relatively uniform intensity distribution of a planar lighting source is needed for a specific lighting application such as back-lighting (BL) for liquid-crystal displays (LCD) in which Regular white LED's (WLED) and light-guide plate are assembled as a planar module. Our intensity measurement of a WOLED revealed a unique pattern in which the relative intensities near central area are higher than that near the edge of the emissive area. This unique intensity profile is similar to the feature of Gaussian distribution function. Our preliminary result of applying Gaussian distribution function to numerically characterize the intensity profile of a WOLED suggests that the unique intensity profile can be represented by single distribution function properly.
The feasibility of applying multiple white organic light-emitting diodes (WOLED) to establish specific planar illuminative patterns for general lighting without secondary optical components was experimentally investigated in smaller scale by using a single-axis automatic optical measuring system. Regular white light-emitting diodes (WLED) usually require secondary optical components to transform its point-source optical characteristics into specific planar illuminative pattern for general lighting application. WOLED has become a potential planar lighting source due to its unique device structure. The lighting source in our experiment consists of three WOLED's mounted side-by-side with changeable tilting angle. This adjustable lighting source with three planar WOLED's may be feasible for forming required illuminative pattern without using secondary optical components. Our preliminary experimental result measured from a 3-WOLED source with specific tilting angle in smaller scale suggests that a relatively uniform illuminative area can be established in practical mean without secondary optical components.
KEYWORDS: Light sources and illumination, Near field optics, Optical testing, Organic light emitting diodes, Optical design, Light emitting diodes, Control systems, Solids, Glasses, LED lighting
The far-field optical distribution characteristics of a planar white organic light-emitting diode (WOLED) source with 10x10mm2 emissive area were experimentally investigated and compared to that of a near point-source white light-emitting diode (WLED) as control by using an automatic 2-axis optical measuring system in hemi-spherical space. WOLED has become a potential planar lighting source due to its single device structure consisted of multiple organic layers sandwiched by cathode and anode electrodes on glass substrate. The far-field optical distribution profiles and characteristics of a planar lighting source are crucial for optical design work in specific application. The far-field optical distribution characteristics of a planar WOLED source is expected to be unique and different compared to that of a near point source WLED. Our experimental result indicates that the far-field optical distribution function measured from near point-source WLED is close to that predicted by an ideal Lambertian source. The far-field optical distribution function measured from the planar WOLED source with 10x10 mm2 emissive area reveals slightly different characteristics around normal direction from that of the near point-source WLED.
The thermal conductivity of the organic light-emitting material in a white organic light-emitting diode (WOLED) was
precisely estimated by solving two-dimensional transient heat transfer equation and fitting experimental data. A WOLED
usually operates in relatively high current mode to maintain higher brightness for lighting application. A practical
solution for heat dissipation is crucial for properly applying WOLED in lighting application. Thermal conductivity of a
material is a critical parameter for developing heat dissipation solution. A typical WOLED consists of several thin
organic light-emitting layers with similar thermal characteristics sandwiched by anode and cathode. These organic layers
can be regarded as a single organic light-emitting material for simplifying thermal analysis. The thermal characteristic of
the organic light-emitting material can be represented by an effective or equivalent thermal conductivity in analytical
model. The analytical model of temperature distribution was obtained from solving two-dimensional transient heat
transfer equation with simplified bi-layer structure. The effective thermal conductivity of the thin-film organic
light-emitting material can be precisely estimated by fitting analytical temperature distribution function to the
experimental data. Our preliminary investigation indicates that the thermal conductivity of the organic light-emitting
material is estimated between 0.28 and 0.29 w/m°C, similar to well-known organic compounds.
The optical distribution of a white organic light-emitting diode (WOLED) with 10x10mm2 emitting area was
experimentally investigated and profiled by using a microscopic goniometer associated with energy analyzer in which
the optical power on focusing spot in emitting area can be independently analyzed. Its optical distribution profile can be
established by the interrelation between the relative intensity and position around emitting area. WOLED has become a
potential planar lighting source due to its unique device structure consisted of multiple organic layers sandwiched by
cathode and anode electrodes on glass substrate. The optical distribution of a WOLED planar lighting source is ideally
expected to be uniform distribution around emitting area. Our experimental result measured from two independent
WOLED samples reveals a unique distribution in which the relative intensity in central area is higher than that near the
edge around emitting area. Its optical profile is similar to Gaussian distribution rather than uniform distribution as
observed by naked eyes. It is also indicated that the optical profile of a WOLED planar lighting source is analogous to a
point lighting source in microscopic point of view.
The dynamical degradation process of operating organic light-emitting diode (OLED) was proposed and investigated by
non-destructive reflectivity measurements using a p-polarized He-Ne laser as probing tool. The intrinsic OLED
degradation mechanism mainly depends on intermediate layers at organic/electrode interfaces. The optical behavior of
these interfacial dielectric layers and corresponding optical parameters may be capable of representing OLED
degradation in macroscopic aspect. Optical parameters defined as optical constants (n, k) and thickness (d) were obtained
from fitting our experimental data to a theoretical model including interfacial dielectric layers with (n, k, d) as adjustable
parameters. Our experimental results revealed that the change of the reflectivity spectra obtained from static and operated
OLED was observable. The tendency of change in reflectivity spectra can be used as qualitative and dynamical aspect of
degradation of operating OLED. The dynamical degradation process can be quantitatively modeled by inspecting the
variation of optical parameters. This dynamical aspect may also include time-dependent information of degradation as
operating OLED. Our data-fitting results indicated that optical constants of intermediate layers have a trend to increase
as OLED from static to turn-on status. The thickness of intermediate layers obtained from data-fitting ranged from 0.2 to
14nm, satisfying our expectation. The reflective spectra obtained from basic OLED with ITO/Alq3/LiF/Al structure
revealed a clear dip located around 61.5° incident angle from ITO glass side as OLED in turn-on status. It indicated that
surface plasma resonance may occur even in OLED layer structure.
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