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35 results on '"Krames, M. R."'

4. Colour gamut size and shape influence colour preference.

Author

Wei, M., Houser, K. W., David, A., and Krames, M. R.

Subjects
PSYCHOLOGY of color, PSYCHOLOGICAL tests, SIZE, GEOMETRIC shapes, PSYCHOLOGICAL techniques, PSYCHOLOGY
Abstract

Two psychophysical experiments were conducted to investigate the effect of colour gamut size and shape on colour preference. In the first, two side-by-side booths were designed to resemble a retail setting with clothing; in the second, a single booth was designed to resemble a restaurant setting, but also included a mirror to permit the observer's evaluation of skin tone. These settings were illuminated with two sets of sources, where, compared to a fixed reference, one set created modest chroma enhancement and the other set created greater increases in object chroma. Within each set, gamut shape varied, meaning different hues were saturated, even though, on average, the spectra created the same average increase in chroma. When objects were unfamiliar, as with the fabrics, all chroma-enhancing spectra were preferred to the fixed reference regardless of the gamut shapes. When familiar objects were present, such as food, observers were more discerning about changes in chroma and hue. We conclude that a graphic of gamut shape is an important adjunct to average measures of colour fidelity and gamut. [ABSTRACT FROM AUTHOR]

Published
2017
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5. Long wavelength (λ∼1.5 μm) native-oxide-defined InAlAs-InP-InGaAsP quantum well heterostructure laser diodes.

Author

Caracci, S. J., Krames, M. R., Holonyak, N., Ludowise, M. J., and Fischer-Colbrie, A.

Subjects
*OXIDATION, *INDIUM compounds, *HETEROSTRUCTURES
Abstract

Studies the native oxidation of indium compound employed to fabricate long wavelength indium compound quantum well heterostructure laser diodes. Applications of native oxide process; Preparation of the sample; Discussion on the results of the study.

Published
1994
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7. Perceptual responses to LED illumination with colour rendering indices of 85 and 97.

Author

Wei, M., Houser, K. W., David, A., and Krames, M. R.

Subjects
LED lighting, LUMINOUS flux, COLOR temperature, OPTICAL brighteners, ENERGY consumption
Abstract

A light source’s ability to render colours and whites is one aspect of lighting quality. Since better colour rendition generally comes with a penalty in luminous efficacy, it is reasonable to consider the balance: Should colour and whiteness rendition be sacrificed to achieve higher efficacy? Here, we investigate perceptual responses under illumination from two sources, a blue-pumped LED with a colour rendering index of 85 (BLED85), and a violet-pumped LED with a colour rendering index of 97 (VLED97). Forty-eight participants completed three experiments. Neutral, red, and pink were preferred under VLED97. Skin rendition was preferred by Caucasians under VLED97; Asians had no preference. Teeth and a white shirt were whiter and more preferred under VLED97. We conclude that the colour and whiteness rendition must be considered on a par with luminous efficacy. [ABSTRACT FROM AUTHOR]

Published
2015
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18. High-power AlGaInN flip-chip light-emitting diodes

Author

Wierer, J. J., primary, Steigerwald, D. A., additional, Krames, M. R., additional, O’Shea, J. J., additional, Ludowise, M. J., additional, Christenson, G., additional, Shen, Y.-C., additional, Lowery, C., additional, Martin, P. S., additional, Subramanya, S., additional, Götz, W., additional, Gardner, N. F., additional, Kern, R. S., additional, and Stockman, S. A., additional

Published
2001
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20. High-power truncated-inverted-pyramid (AlxGa1−x)0.5In0.5P/GaP light-emitting diodes exhibiting >50% external quantum efficiency

Author

Krames, M. R., primary, Ochiai-Holcomb, M., additional, Höfler, G. E., additional, Carter-Coman, C., additional, Chen, E. I., additional, Tan, I.-H., additional, Grillot, P., additional, Gardner, N. F., additional, Chui, H. C., additional, Huang, J.-W., additional, Stockman, S. A., additional, Kish, F. A., additional, Craford, M. G., additional, Tan, T. S., additional, Kocot, C. P., additional, Hueschen, M., additional, Posselt, J., additional, Loh, B., additional, Sasser, G., additional, and Collins, D., additional

Published
1999
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32. Gain comparison in polar and nonpolar/semipolar gallium-nitride-based laser diodes.

Author

Melo, T., Y-LHu, Weisbuch, C., Schmidt, M. C., David, A., Ellis, B., Poblenz, C., Lin, Y.-D., Krames, M. R., and Raring, J. W.

Subjects
GALLIUM nitride, DIODES, LASERS, FABRY-Perot interferometers, CURRENT density (Electromagnetism), ELECTRIC fields, SPECTRUM analysis, PHYSICS experiments
Abstract

Experimental gain spectra at continuous-wave (CW) operation of laser diodes (LDs) fabricated from c-plane, nonpolar and semipolar GaN-based materials emitting in violet, blue and green spectral regions are presented. Gain spectra were obtained using the Hakki-Paoli method at high resolution. The ability of the setup to resolve the sharp Fabry-Perot longitudinal peaks of the lasers at all injection currents allowed us to accurately measure the current density to reach transparency on the devices characterized in this work, and determine both total losses and differential modal gain curves up to threshold. We present a comparison of transparency current density and modal gain for nonpolar and c-plane LDs in violet and blue regions. The main parameters for the analysis are the internal electric fields (for c-plane lasers), hole effective masses and valence band splittings. In a preliminary analysis, we investigated the gain spectrum of semipolar green LDs and observed a significantly lower total linewidth (homogeneous plus inhomogeneous) than reported elsewhere, which seems to indicate that inhomogeneous broadening is not the main issue governing the evolution toward high performance green LDs [ABSTRACT FROM AUTHOR]

Published
2012
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34. Blue-emitting InGaN–GaN double-heterostructure light-emitting diodes reaching maximum quantum efficiency above 200 A/cm2.

Author

Gardner, N. F., Müller, G. O., Shen, Y. C., Chen, G., Watanabe, S., Götz, W., and Krames, M. R.

Subjects
LIGHT emitting diodes, GALLIUM nitride, INDIUM alloys, HETEROSTRUCTURES, QUANTUM efficiency, METAL organic chemical vapor deposition
Abstract

Auger recombination is determined to be the limiting factor for quantum efficiency for InGaN–GaN (0001) light-emitting diodes (LEDs) at high current density. High-power double-heterostructure (DH) LEDs are grown by metal-organic chemical vapor deposition. By increasing the active layer thickness, DH LEDs can reach a maximum in quantum efficiency at current densities above 200 A/cm2. Encapsulated thin-film flip-chip DH LEDs with peak wavelength of 432 nm have an external quantum efficiency of 40% and output power of 2.3 W at 2 A. [ABSTRACT FROM AUTHOR]

Published
2007
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35. Blue-emitting InGaN–GaN double-heterostructure light-emitting diodes reaching maximum quantum efficiency above 200 A/cm2.

Author

Gardner, N. F., Müller, G. O., Shen, Y. C., Chen, G., Watanabe, S., Götz, W., and Krames, M. R.

Subjects
*LIGHT emitting diodes, *GALLIUM nitride, *INDIUM alloys, *HETEROSTRUCTURES, *QUANTUM efficiency, *METAL organic chemical vapor deposition
Abstract

Auger recombination is determined to be the limiting factor for quantum efficiency for InGaN–GaN (0001) light-emitting diodes (LEDs) at high current density. High-power double-heterostructure (DH) LEDs are grown by metal-organic chemical vapor deposition. By increasing the active layer thickness, DH LEDs can reach a maximum in quantum efficiency at current densities above 200 A/cm2. Encapsulated thin-film flip-chip DH LEDs with peak wavelength of 432 nm have an external quantum efficiency of 40% and output power of 2.3 W at 2 A. [ABSTRACT FROM AUTHOR]

Published
2007
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