Due to the efforts of Henry Warren, inventor of the Telechron electric clock, electric power companies have been a source of time and frequency reference for the public for over a hundred years. However, advances in technology and changes in the electric power industry have generated a movement within the industry to end the time-reference service. Power systems in the U.S. operate at a nominal 60 Hz, but in actual operation they accumulate significant phase error. It must be deliberately backed out to keep synchronous clocks on time-a procedure known as Time Error Correction (TEC). Today, many electric clocks still depend on the power system as the reference oscillator-that is, are synchronous-while others use other time references, such as local quartz oscillators and networked time servers-a benefit of the Internet of Things. Little is known about the overall impact of TEC on timekeeping in modern times. The Blackout of 2003 spawned a new regulatory structure for the electric power industry to improve reliability, and as an unanticipated side effect, a decision process that would most likely eliminate TECs was set in motion. The specific proposal is to retire regulatory standards designated BAL-004 and WEQ-006. We review the relevant structure and governing bodies of the U.S. power grids, and report on the current procedural status of these standards. In addition, we review possible scenarios for the future of the power system as an elapsed-time reference absent TEC. For this, we include analysis of the electric power at USNO, as measured over five years. The TECs appear in the data; an analysis with the industry-supplied record of the TECs indicates that without them a time deviation of about 7 1/2 minutes would have occurred on the Eastern Interconnection (grid) between the daylight saving time switches of March 2016 and November 2016.

The influences of GaI3, InI, and TlI on the evaporation characteristics of CeI3 have been studied over the temperature range 900 K to 1400 K using x-ray induced fluorescence. The total vapor densities, summed over all atomic and molecular species, of Ce, I, In, and Tl were obtained. Measurements of Ce were limited to temperatures above 1033 K, the melting temperature of CeI3. This is the highest temperature range for which measurements of the vapor pressure of CeI3 have been made. The vapor pressure of the CeI3 monomer above the pure CeI3 salt for temperatures exceeding its melting point can be approximated by log10p/Pa=11.24(±0.03)−10,690(±40) (T/K)−1 where the numbers in parentheses are standard uncertainties. InI and TlI were shown to modestly enhance the presence of Ce in the vapor phase, up to a factor of 5. GaI3 produced no enhancement in this temperature range. Numerical simulations of the thermochemical equilibrium suggest the importance of both liquid-phase and vapor-phase complexes. Significant improvement to the method of absolute calibration is discussed.

The vapors in equilibrium with condensates of DyI3, DyI3/InI, TmI3, and TmI3/TlI were observed over the temperature range from 900 K to 1400 K using x-ray induced fluorescence. The total densities of each element (Dy, Tm, In, Tl, and I) in the vapor, summed over all atomic and molecular species, were determined. Dramatic enhancements in the total vapor densities of Dy and Tm were observed in the vapors over DyI3/InI and TmI3/TlI as compared to the vapors over pure DyI3 and pure TmI3, respectively. An enhancement factor exceeding 10 was observed for Dy at T ≈ 1020 K, decreasing to 0 at T ≈ 1250 K. An enhancement factor exceeding 20 was observed for Tm at T ≈ 1040 K, decreasing to 0 at T ≈ 1300 K. Such enhancements are expected from the formation of the vapor-phase hetero-complexes DyInI4 and TmTlI4. Numerical simulations of the thermo-chemical equilibrium suggest the importance of additional complexes in liquid phases. A description of the measurement technique is given. Improvements in the absolute calibration lead to an approximately 40% correction to previously reported preliminary results [J. J. Curry et al., Chem. Phys. Lett. 507, 52 (2011); Appl. Phys. Lett. 100, 083505 (2012)].

Total vapor-phase densities of Dy in equilibrium with a DyI3/InI condensate and Tm in equilibrium with a TmI3/TlI condensate have been measured for temperatures between 900 K and 1400 K. The measurements show strong enhancements in rare-earth vapor densities compared to vapors in equilibrium with the pure rare-earth metal-halides. The measurements were made with x-ray induced fluorescence on the sector 1-ID beam line at the Advanced Photon Source. The temperature range and salt mixtures are relevant to the operation of metal-halide high-intensity discharge lamps.

Measurement of light is an old subject, though the past 100 years have seen significant advances. 100 years ago, photometry - the art and science of measuring light as it is perceived by people - had the greater technological importance. Even today SI (the metric system) retains a base unit for photometry, the candela. However, early work at NBS included pivotal projects in the field of radiometry - the measurement of the physical characteristics of light. These included the validation of Planck's newly-minted theory of blackbody radiation, determining the radiation constants with good accuracy, and the definitive analysis of the spectral responsivity of human vision, so as to relate photometry to radiometry. This latter work has only increased in importance over the past 75 years as the definition of the candela has changed and improved. Today, NIST makes radiometric, and hence photometric measurements, with unprecedented precision. Cryogenic radiometers based on the principle of electrical substitution measure optical flux with uncertainties of 0.02%. Additional facilities enable measurement of spectral responsivity, spectral radiance, and spectral irradiance. Novel detectors, such as light-traps, allow the best accuracy to be transferred from the primary standards to routinely-used instruments and to calibration customers. Filtered detectors are used to realize photometric scales, radiation temperature scales, and other specialized measurements. Indeed, the story of the metrology of light is the story of continuous improvement, both driven by and enabled by advances in technology. We touch upon some of these as a prelude to the other talks in this Conference.

Measurement of light is an old subject, though the past 100 years have seen significant advances. 100 years ago, photometry-the art and science of measuring light as it is perceived by people-had the greater technological importance. Even today, SI (the metric system) retains a base unit for photometry, the candela. However, early work at NBS included pivotal projects in the field of radiometry-the measurement of the physical characteristics of light. These included the validation of Planck's newly-minted theory of blackbody radiation, determining the radiation constants with good accuracy, and the definitive analysis of the spectral responsivity of human vision, so as to relate photometry to radiometry. This latter work has only increased in importance over the past 75 years as the definition of the candela has changed and improved. Today, NIST makes radiometric, and hence photometric measurements, with unprecedented precision. Cryogenic radiometers based on the principle of electrical substitution measure optical flux with uncertainties of 0.02 %. Additional facilities enable measurement of spectral responsivity, spectral radiance, and spectral irradiance. Novel detectors, such as light-traps, allow the best accuracy to be transferred from the primary standards to routinely-used instruments and to calibration customers. Filtered detectors are used to realize photometric scales, radiation temperature scales, and other, specialized measurements. Indeed, the story of the metrology of light is the story of continuous improvement, both driven by and enabled by advances in technology. We touch upon some of these as a prelude to the other talks in this Conference.

Autoionization of valence and Rydberg states in NO over the 12.5--18 eV photon energy range was studied by vibrationally resolved photoelectron spectroscopy of the 2 pi orbital. Complex, oscillatory structure is observed in NO+ (2 pi (-1)) X(1)Sigma (+) partial cross sections, branching ratios, and photoelectron anisotropy parameters due to autoionizing valence states and Rydberg slates associated with the 1 pi (-1) and 5 sigma (-1) channels. Autoionization of the 5 sigma --> np(pi, sigma) (v' = 0), n = 3-5 Rydberg states leading to the (5 sigma (-1)) b(3) IIstate of NO+ produces very high vibrational levels of (2 n(-1)) X(1)Sigma (+). Autoionization of the 5 sigma --> 3p pi (v' = 0) Rydberg

A new calibration method has been developed to improve the accuracy of chromaticity coordinates obtained from a tristimulus colorimeter for color displays. Matrix methods such as the one recommended by ASTM are well known for this purpose, but they may fail to work as expected due to experimental noise and errors. As these matrix methods are based on tristimulus values, the accuracy of the luminance measurement affects the accuracy of the corrected chromaticity. This new method utilizes x, y values only, and is independent of y values. Thus, in principle, it eliminates errors due to luminance measurement variations. A correction matrix is obtained from the x, y values of three primary colors and a white color of a display, measured by the target instrument and a reference instrument. A computer simulation was conducted to evaluate the effect of random noise in y. Experiments were conducted using a commercial tristimulus colorimeter and a spectroradiometer, measuring 14 colors of a CRT display. The results show noticeable improvement in chromaticity accuracy over the current practice.

It is generally believed that the most accurate means of measuring the CIE tristimulus values X, Y, Z or chromaticity coordinates x,y from a display is by using a spectroradiometer. Nevertheless, tristimulus colorimeters employing three or four colored filters find wide use because of their simplicity and lower cost. These devices cannot be calibrated to give accurate results in all situations because the spectral responsivities of their filtered detectors are not exactly the CIE color-matching functions. However, for a display that produces a linear superposition of three primary colored lights of fixed spectra, a tristimulus colorimeter can be correctly calibrated to measure all colors on that display. Signals from all of the filtered detectors are used to compute each of the X, Y, z values. The calibration matrix is computed by data fitting to a reference colorimeter. An improvement to the previously published method is reported, an a numerical example is shown. This technique is more tractable with today's digital instrumentation than it was when it was discovered, yet it remains underused. The American Society for Testing and Materials, through its Committee on Color and Appearance, is revising its standard on display measurements using tristimulus colorimeters to encourage the adoption of the technique.

Measurements of vibrational branching ratios and photoelectron angular distributions have been made in the regions of the Tanaka-Ogawa, Lindholm, and Henning series for the CO2 molecule. The behavior of these parameters was found to be sensitive to which particular resonance is excited, with considerable intensity going into vibrational modes other than the symmetric stretch. An initial analysis of some of the data taken is presented.

It is generally believed that the most accurate means of measuring the CIE tristimulus values X, Y, Z or chromaticity coordinates x,y from a display is by using a spectroradiometer. Nevertheless, tristimulus colorimeters employing three or four colored filters find wide use because of their simplicity and lower cost. These devices cannot be calibrated to give accurate results in all situations because the spectral responsivities of their filtered detectors are not exactly the CIE color-matching functions. However, for a display that produces a linear superposition of three primary colored lights of fixed spectra, a tristimulus colorimeter can be correctly calibrated to measure all colors on that display. Signals from all of the filtered detectors are used to compute each of the X, Y, z values. The calibration matrix is computed by data fitting to a reference colorimeter. An improvement to the previously published method is reported, an a numerical example is shown. This technique is more tractable with today's digital instrumentation than it was when it was discovered, yet it remains underused. The American Society for Testing and Materials, through its Committee on Color and Appearance, is revising its standard on display measurements using tristimulus colorimeters to encourage the adoption of the technique.

Measurements of the vibrational branching ratios and photoelectron angular distributions have been made in the regions of the Tanaka-Ogawa, Lindholm and Henning series for the CO2 molecule. The behaviour of these parameters was found to be sensitive to which particular resonance is excited, with considerable intensity going into vibrational modes other than the symmetric stretch. An initial analysis of some of the data taken is presented.

A high-accuracy cryogenic radiometer has been developed at the National Institute of Standards and Technology to serve as a primary standard for optical power measurements. This instrument is an electrical-substitution radiometer that can be operated at cryogenic temperatures to achieve a relative standard uncertainty of 0.021% at an optical power level of 0.8 mW. The construction and operation of the high-accuracy cryogenic radiometer and the uncertainties in optical power measurements are detailed.

The Système International des Unités (SI) base unit for photometry, the candela, has been realized by using absolute detectors rather than absolute sources. This change in method permits luminous intensity calibrations of standard lamps to be carried out with a relative expanded uncertainty (coverage factor k = 2, and thus a 2 standard deviation estimate) of 0.46 %, almost a factor-of-two improvement. A group of eight reference photometers has been constructed with silicon photodiodes, matched with filters to mimic the spectral luminous efficiency function for photopic vision. The wide dynamic range of the photometers aid in their calibration. The components of the photometers were carefully measured and selected to reduce the sources of error and to provide baseline data for aging studies. Periodic remeasurement of the photometers indicate that a yearly recalibration is required. The design, characterization, calibration, evaluation, and application of the photometers are discussed.

The candela, one of the SI base units, has been realized by using absolutely calibrated detectors rather than sources. A group of eight photometers was constructed using silicon photodiodes, precision apertures, and glass filters for V (λ) match. Their absolute spectral responsivities were calibrated against the NIST absolute spectral responsivity scale. The measurement chain has been significantly shortened compared with the old scale based on a blackbody. This resulted in improving the calibration uncertainty to 0.46% (2σ), a factor-of-2 improvement. This revision has made various photometric calibrations at NIST more versatile and flexible. Luminous intensities of light sources ranging from 10 -3 to 10 4 candelas are directly calibrated with the standard photometers, which have a linear response over that range. Illuminance meters are calibrated directly against the standard photometers. A luminance scale has also been realized on the detector base using an integrating sphere source. Total flux ranging from 10 -2 to 10 5 lumens can be measured in a 2 m integrating sphere using a photometer with a wide dynamic range. The revisions of the calibration procedures significantly improved the calibration uncertainty.

The Système International base unit for photometry, the candela, has been realized by using absolute detectors rather than absolute sources. This change in method permits luminous intensity calibrations of standard lamps with an expanded uncertainty of 0.46%, almost a factor-of-2 improvement. A group of eight reference photometers has been constructed with silicon photodiodes, matched with filters to mimic the Commission Internationale de l'Eclairage spectral luminous efficiency function for photopic vision.The design, characterization, calibration, evaluation, and further application of the photometers are discussed.