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The extraction of guided modes from a standard light-emitting heterostructure similar to those of visible or near-infrared light-emitting diodes is discussed.

We study the high-temperature electroluminescence properties of 600 nm InGaN red 40 × 40 μm2 micro-light-emitting diodes (μLEDs) with a peak external quantum efficiency (EQE) of 3.2%. Temperature-dependent peak wavelength measurements show a low redshift of 0.05 nm/K. The injection efficiency improves with increasing temperature. The hot/cold (HC) factor is used to quantify the thermal droop: at 400 K, the EQE and wall-plug efficiency HC factors at 50 A/cm2 reach high values of 0.72 and 0.85, respectively. This demonstrates the robustness of InGaN red μLEDs up to high temperature, with a much-improved stability over conventional AlInGaP red μLEDs. [ABSTRACT FROM AUTHOR]

This article describes a way to distinguish between two distinct components of light source–induced color shifts, base color shift and metameric color shift, to provide a more complete understanding of color rendition. Working within the existing framework of IES TM-30-18 and CIE 224:2017, it shows that base color shift varies smoothly with location in color space in a pattern that is determined by the spectral power distribution (SPD) of the light source. Patterns of smooth variation can often be approximated well with a low-order polynomial function. Here, a vector field model is presented, based on a second-order polynomial function. The polynomial coefficients are adjusted, for a given light source, to provide a least squares fit to the calculated color shifts of a standard set of color samples. The adequacy of this model was verified by comparing it to another approach for characterizing base color shift that is based on discretization of color space and a much larger set of color samples. Once the vector field model of base color shifts for a given light source is determined, the metameric color shifts can be calculated from the residuals and the distribution of those shifts can be statistically summarized. Based on this information, a metameric uncertainty index (Rt) is proposed to provide new information about a light source. In particular, it can be used to estimate the likelihood of noticeable metameric mismatches induced by a given light source, which could lead to improved predictions of the perceived color quality of light. [ABSTRACT FROM AUTHOR]

Recently, a group including the present authors developed a new color rendering (fidelity) measure, approved by the IES and henceforth referred to as IESRf, that has two major updates with respect to the general color rendering indexRaof the CIE. First, it proposes an update to the more perceptually uniform CAM02-UCS color space. Secondly, instead of using only a small number (eight) of moderately saturated samples to determine a general color fidelity index, the IES method proposes using a set of 99 samples uniformly distributed in color space. In addition to the latter, the sample set has one other important property: spectral uniformity. This ensures that the sample set is not wavelength biased: all wavelengths contribute equivalently to the general color fidelity score. This article explores the importance of these two updates for color fidelity evaluation. It shows how the color space update results in a substantial spread of the new color fidelity scores relative to the old CIERavalues and how the sample set update results in an overall reduction of color fidelity scores for most light source spectra with high CIERa(≥80) and high luminous efficacy of radiation (LER) values, especially those with narrowband or spiked spectral features. It is shown that calculated color fidelity scores are affected by the degree of sample set spectral uniformity and that, in the absence of sample set spectral uniformity, light source spectra can be tuned to yield anomalously high CIERavalues without necessarily yielding an increase in actual perceived color fidelity. [ABSTRACT FROM PUBLISHER]

We study the use of large reflectance sample sets to assess the color fidelity of light sources. We introduce three data sets covering a large fraction of the color space and a method to compute color fidelity over these sets. By applying this calculation to various source spectra, we show that some sources have significantly lower fidelity than would be predicted using the eight samples of the color rendering index. Structured and truncated source spectra are especially prone to this pitfall, whereas broad and smooth spectra are more resilient. [ABSTRACT FROM PUBLISHER]

We discuss a method to evaluate the color rendition of light sources, which improves upon the well-known Color Rendering Index. The method combines two measures (for color fidelity and gamut), and employs an optimized set of reflectance test samples. It is proposed as the basis for the upcoming IES Color Rendition Measure, and is proposed for consideration with the CIE. [ABSTRACT FROM AUTHOR]