Development of the IES method for evaluating the color rendition of light sources.

We have developed a two-measure system for evaluating light sources' color rendition that builds upon conceptual progress of numerous researchers over the last two decades. The system quantifies the color fidelity and color gamut (change in object chroma) of a light source in comparison to a reference illuminant. The calculations are based on a newly developed set of reflectance data from real samples uniformly distributed in color space (thereby fairly representing all colors) and in wavelength space (thereby precluding artificial optimization of the color rendition scores by spectral engineering). The color fidelity score R(f) is an improved version of the CIE color rendering index. The color gamut score R(g) is an improved version of the Gamut Area Index. In combination, they provide two complementary assessments to guide the optimization of future light sources. This method summarizes the findings of the Color Metric Task Group of the Illuminating Engineering Society of North America (IES). It is adopted in the upcoming IES TM-30-2015, and is proposed for consideration with the International Commission on Illumination (CIE).

Defining the visual adaptation field for mesopic photometry: How does the high-luminance source affect peripheral adaptation?

CIE 191:2010 recommends the mesopic photometry system, in which the luminous efficiency function is determined from the adaptation luminance. However, it cannot be implemented because the adaptation field to determine the adaptation luminance is not defined. Surrounding luminance effect is a key factor to define the adaptation field. Vision experiments have been conducted to measure the surrounding luminance effect on peripheral adaptation state with a point source at varied intensities placed at different position. The results reveal that the effect can be described as veiling luminance and that the magnitude of the effect is larger than that of the foveal veiling luminance. A model for the peripheral veiling luminance proposed by Stiles and Crawford in 1937 shows the best prediction for the surrounding luminance effect.

Simple spectral stray light correction method for array spectroradiometers.

A simple, practical method has been developed to correct a spectroradiometer's response for measurement errors arising from the instrument's spectral stray light. By characterizing the instrument's response to a set of monochromatic laser sources that cover the instrument's spectral range, one obtains a spectral stray light signal distribution matrix that quantifies the magnitude of the spectral stray light signal within the instrument. By use of these data, a spectral stray light correction matrix is derived and the instrument's response can be corrected with a simple matrix multiplication. The method has been implemented and validated with a commercial CCD-array spectrograph. Spectral stray light errors after the correction was applied were reduced by 1-2 orders of magnitude to a level of approximately 10(-5) for a broadband source measurement, equivalent to less than one count of the 15-bit-resolution instrument. This method is fast enough to be integrated into an instrument's software to perform real-time corrections with minimal effect on acquisition speed. Using instruments that have been corrected for spectral stray light, we expect significant reductions in overall measurement uncertainties in many applications in which spectrometers are commonly used, including radiometry, colorimetry, photometry, and biotechnology.