We have developed a spectral model for describing the shape of the emission spectrum of InGaAlP-based red light-emitting diodes (LEDs) with quantum-well structure. The model is based on Maxwell-Boltzmann distribution with junction temperature T j and an experimental twodimensional joint density of states (DOS). We model the DOS with a sum of two exponentially broadened step functions describing the two lowest sub-bands in semiconductor quantum well. The relative locations DE 1 ¼ 0 meV and DE 2 ¼ 112.7 meV above the band gap energy E g ¼ 1.983 eV and the ratio 2.13 of the step heights were fixed using an experimental DOS extracted from a LED spectrum measured at known T j and driving current I. The model can then be fitted to other spectra of other LED samples at varied T j and I by varying the fitting parameters E g ; T j , and the broadening of the sub-band edges. The model was tested for three LED samples over I ¼ 200-370 mA and T j ¼ 303-398 K. Junction temperatures obtained by modeling were compared with calibrated T j obtained by the forward voltage method. The mean absolute difference was about 2.9 K (0.8%) over the whole region studied and the maximum difference was 8.5 K. The thermal coefficient measured for E g was À0.509 meV K À1. For the first and second sub-band edges, the thermal broadening coefficients were 18 leV K À1 and 37 leV K À1 , respectively. V
The transmittance minima of 18 absorption bands of a solution of 40 g/L holmium oxide in 10% (volume fraction) perchloric acid are certified as intrinsic traceable wavelength standards, by means of a multicenter measurement on material from a single source coupled with comparisons of a variety of preparations of the material evaluated on a single instrument. Fit-for-purpose artifact standards for the experimental calibration or validation of wavelength scales of chemical spectrophotometers can be carefully produced by end users themselves or by commercial standards producers. The intrinsic (data) standard confers traceability to the SI unit of length in place of costly transfer artifacts and repetitive calibration procedures. Certified values are provided for instrumental spectral bandwidths of 0.1–3.0 nm in 0.1 nm intervals, and information values are provided to a spectral bandwidth of 10 nm at wider intervals. Expanded uncertainties are typically less than ±0.1 nm for certified band positions.
Highly polished plane gloss standards are indispensable when using a glossmeter. The gloss value of a primary reference standard is defined by its refractive index at 589.3 nm. This definition allows ease of use, but the calibration accuracy is limited to about ±0.5% due to inconsistency between the monochromatic definition and the polychromatic use in the glossmeter. Detector-based radiometry has improved a lot in the last 20 years and it is now time to think about changing the primary gloss standard calibration to absolute specular reflectance-based measurements. This paper is a step into this direction. It shows a refractive index fitting method for gloss standards based on gonioreflectometric specular-reflection measurements, Fresnel's equation and least-squares fitting. The refractive index fitted data showed ±0.23% agreement on average with the gonioreflectometric data measured in 1˚steps and ±0.07% agreement on average for the angular corrected data. The requirement for an uncertainty of ±0.1% in the gonioreflectometric calibration was also analysed.
Band filter radiometry has recently become popular. Its application for detector-based spectral-irradiance measurements requires improved characterization of standard lamps. This paper presents an approximation function for the spectral irradiance of NPL/GEC and FEL lamp data, reported in the 1990 international comparison measurements of the Consultative Committee for Photometry and Radiometry (CCPR). Characterization with a minimum number of parameters, applicable within the visible spectral range, is attempted. Since the spectral emissivity of tungsten is nearly linear in the spectral range from 400 nm to 900 nm, the irradiance of the standard lamps was approximated with three parameters, representing a linear polynomial multiplied by the Planck function. The same linear polynomial was used for each lamp of the same type, and was fitted only for temperature and intensity. The average difference between the measured and the approximated data was found to be less than 0.085 % for the NPL/GEC lamps and less than 0.095 % for the FEL lamps. This means that the relative spectral emissivity of each lamp of the same type is practically the same. The temperature fitting was characterized by the average difference between the measured and approximated data in the ultraviolet and infrared spectral ranges.
Detector-based bandfilter radiometry has recently become increasingly popular in the fields of absolute spectral-irradiance measurements, black-body temperature determination and comparison with sourcebased measurements. This paper introduces an advanced data-reduction method which handles all bandfilter measurements together. An analytical function approximation is used on Planckian radiation multiplied by a polynomial emissivity.
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