Browsing by Subject "Color rendering index"

Now showing 1 - 7 of 7

Open Access
A bright cadmium-free, hybrid organic/quantum dot white light-emitting diode
(American Institute of Physics, 2012-12-06) Yang, X.; Divayana, Y.; Zhao, D.; Swee Leck, K.; Lu, F.; Tiam Tan, S.; Putu Abiyasa, A.; Zhao Y.; Demir, Hilmi Volkan; Wei Sun, X.
We report a bright cadmium-free, InP-based quantum dot light-emitting diode (QD-LED) with efficient green emission. A maximum brightness close to 700 cd/m2 together with a relatively low turn-on voltage of 4.5 V has been achieved. With the design of a loosely packed QD layer resulting in the direct contact of poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl) benzidine] (poly-TPD) and 2,2′,2″-(1,3,5-benzinetriyl)-tris(1- phenyl-1-H-benzimidazole) (TPBi) in the device, a ternary complementary white QD-LED consisting of blue component (poly-TPD), green component (QDs), and red component (exciplex formed at the interface between poly-TPD and TPBi) has been demonstrated. The resulting white QD-LED shows an excellent color rendering index of 95.
Open Access
Energy-saving quality road lighting with colloidal quantum dot nanophosphors
(Walter de Gruyter GmbH, 2014) Erdem, T.; Kelestemur, Y.; Soran-Erdem, Z.; Ji, Y.; Demir, Hilmi Volkan
Here the first photometric study of road-lighting white light-emitting diodes (WLEDs) integrated with semiconductor colloidal quantum dots (QDs) is reported enabling higher luminance than conventional light sources, specifically in mesopic vision regimes essential to street lighting. Investigating over 100 million designs uncovers that quality road-lighting QD-WLEDs, with a color quality scale and color rendering index ≥85, enables 13-35% higher mesopic luminance than the sources commonly used in street lighting. Furthermore, these QD-WLEDs were shown to be electrically more efficient than conventional sources with power conversion efficiencies ≥16-29%. Considering this fact, an experimental proof-of-concept QD-WLED was demonstrated, which is the first account of QD based color conversion custom designed for street lighting applications. The obtained white LED achieved the targeted mesopic luminance levels in accordance with the road lighting standards of the USA and the UK. These results indicate that road-lighting QD-WLEDs are strongly promising for energy-saving quality road lighting. © 2014 Science Wise Publishing & De Gruyter 2014.
Open Access
Metrics for light source design
(Springer, 2019-01) Erdem, Talha; Demir, Hilmi Volkan; Erdem, Talha; Demir, Hilmi Volkan
In this part of this brief, we summarize the metrics that need to be considered for designing light sources. We start with metrics on the shade of color and then continue with color rendering and photometry.
Open Access
Nanocrystal integrated light emitting diodes based on radiative and nonradiative energy transfer for the green gap
(IEEE, 2009) Nizamoğlu, Sedat; Sarı, Emre; Baek J.-H.; Lee I.-H.; Demir, Hilmi Volkan
Recently the photometric conditions for ultra-efficient solid-state lighting have been discussed [1-2]. These studies show that a luminous efficacy of optical radiation at 408 lm/Wopt and a color rendering index (CRI) of 90 at a correlated color temperature (CCT) of 3000 K are achievable at the same time. For this purpose light emitting diodes (LEDs) emitting in blue, green, yellow, and red colors at 463, 530, 573, and 614 nm with relative optical power levels of 1/8, 2/8, 2/8, and 3/8, are required, respectively [1-2]. Although InxGa1-xN material system is capable to cover the whole visible by changing the In composition (x), it is technically extremely challenging to obtain efficient green/yellow light emitting diodes especially at those wavelengths (i.e., at 530 nm and 573 nm, respectively) due to reduced internal quantum efficiency [2-4]. Furthermore, by using the (Al xGa1-x)1-yInyP quaternary alloy it is also possible to cover from 650 nm to 580 nm. However, the efficiencies significantly decrease towards green. Therefore, there exists a significant gap in the green-yellow spectral regions (known as "the green gap") to make efficient light emitting diodes. To address this green gap problem, we propose and demonstrate proof-of-concept nanocrystal (NCs) hybridized green/yellow light emitting diodes that rely on both radiative energy transfer and nonradiative energy transfer (i.e., FRET-Förster resonance energy transfer) for color conversion on near-ultraviolet (near-UV) LEDs.
Open Access
Novel hybrid light emitting diodes with multiple assemblies of nanocrystals to generate and tune white light
(2007) Nizamoğlu, Sedat
Today approximately one third of the world population (about two billion people) in under-developed countries has no access to electricity and relies on unhealthy, costly and low-quality fuel-based lighting for home illumination. In the rest of the world, lighting consumes a large portion (20%) of the total electricity production, which significantly contributes to global warming problem. Also given limited resources, such large energy consumption needs to be reduced for sustainable economic growth. Solid state lighting provides remedy to these problems for the entire globe. Therefore, the advancement of white light emitting diodes (WLEDs) becomes a key point for development of human civilization. To this end, the strong demand for the development of high quality WLEDs around the globe motivates our research work on the investigation of white light generation with high color rendering index. In this thesis, we develop and demonstrate nanocrystal hybridized light emitting diodes with high color rendering index. By the hybridization of multiple layer-by-layer assemblies of CdSe/ZnS core-shell nanocrystals on blue and near ultraviolet (n-UV) InGaN/GaN light emitting diodes, we show white light generation with highly tunable optical properties such as tristimulus color coordinates, correlated color temperature, and color rendering index. Additionally, by using dual hybridization of nanocrystals in combination with conjugated polymers, we obtain white light sources with high color rendering indices exceeding the requirements of the future solid state lighting applications. In this thesis, we present design, growth, fabrication, experimental characterization and theoretical analysis of these hybrid white LEDs.
Open Access
Power conversion and luminous efficiency performance of nanophosphor quantum dots on color-conversion LEDs for high-quality general lighting
(SPIE, 2012) Erdem, Talha; Nizamoglu, Sedat; Demir, Hilmi Volkan
For high-quality general lighting, a white light source is required to exhibit good photometric and colorimetric performance along with a high level of electrical efficiency. For example, a warm white shade is desirable for indoors, corresponding to correlated color temperatures ≥4000 K, together with color rendering indices ≥90. Additionally, the luminous efficacy of optical radiation (LER) should be high, preferably ≥380 lm/W opt. Conventional white LEDs cannot currently satisfy these requirements simultaneously. On the other hand, color-conversion white LEDs (WLEDs) integrated with quantum dots (QDs) can simultaneously reach such high levels of photometric and colorimetric performance. However, their electrical efficiency performance and limits have been unknown. To understand their potential of luminous efficiency (lm/Welect), we modeled and studied different QD-WLED architectures based on layered QD films and QD blends, all integrated on blue LED chips. The architecture of red, yellow and green emitting QD films (in this order from the chip outwards) is demonstrated to outperform the rest. In this case, for photometrically efficient spectra, the maximum achievable LE is predicted to be 327 lm/W elect. Using a state-of-the-art blue LED reported with a power conversion efficiency (PCE) of 81.3%, the overall WLED PCE is shown to be 69%. To achieve LEs of 100, 150 and 200 lm/Welect, the required minimum quantum efficiencies of the color-converting QDs are found to be 39, 58 and 79%, respectively. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).
Open Access
Superior warm-White light-emitting diodes integrated with quantum dot nanophosphors for high luminous efficacy and color rendering
(Optical Society of America, 2011) Nizamoğlu, Sedat; Erdem, Talha; Sun, X. W.; Demir, Hilmi Volkan
Quantum dot nanophoshor hybridized warm-white LEDs are reported to exhibit high photometric performance of luminous efficacy exceeding 350 lm/Wopt and color rendering index close to 90 at correlated color temperatures <3000 K. ©2011 Optical Society of America.