Conventional Photometer Research Articles

New source and detector technology for the realization of photometric units

The production of incandescent light bulbs is bound to end, as incandescent lighting is being phased out globally in favour of more energy-efficient and sustainable solutions. Temporally stable light-emitting diodes (LEDs) are potential candidates to replace incandescent lamps as photometric source standards. However, traditional V(λ) filter based photometers may have large uncertainty when LEDs are measured instead of incandescent lamps. This is due to the narrow and complicated spectra of LEDs. When the spectra of LEDs are limited to the visible wavelength range, new silicon detector technology can be advantageously exploited in photometry. We present a novel method—based on the recently introduced Predictable Quantum Efficient Detector (PQED)—for the realization of photometric units which completely eliminates the need to use V(λ) filters. Instead, the photometric weighting is taken into account numerically by measuring the relative spectral irradiance. The illuminance values of a blue and a red LED were determined using the new method and a conventional reference photometer. The values obtained by the two methods deviated from each other by −0.06% and 0.48% for the blue and red LED, respectively. The PQED-based values have much lower standard uncertainty (0.17% to 0.18%) than the uncertainty of the values based on the conventional photometer (0.46% to 0.51%).

Design Considerations for Near-Infrared Filter Photometry: Effects of Noise Sources and Selectivity

Optimal filter design of two-channel near-infrared filter photometers is investigated for simulated two-component systems consisting of an analyte and a spectrally overlapping interferent. The degree of overlap between the analyte and interferent bands is varied over three levels. The optimal design is obtained for three cases: a source or background flicker noise limited case, a shot noise limited case, and a detector noise limited case. Conventional photometers consist of narrow-band optical filters with their bands located at discrete wavelengths. However, the use of broadband optical filters with overlapping responses has been proposed to obtain as much signal as possible from a weak and broad analyte band typical of near-infrared absorptions. One question regarding the use of broadband optical filters with overlapping responses is the selectivity achieved by such filters. The selectivity of two-channel photometers is evaluated on the basis of the angle between the analyte and interferent vectors in the space spanned by the relative change recorded for each of the two detector channels. This study shows that for the shot noise limited or detector noise limited cases, the slight decrease in selectivity with the use of broadband optical filters can be compensated by the higher signal-to-noise ratio afforded by the use of such filters. For the source noise limited case, the best quantitative results are obtained with the use of narrow-band non-overlapping optical filters.

Robustness and Noise Voltage Analysis in Two Photometer Circuits

In this paper, a photometer circuit based on a robust two degrees-of-freedom controller is presented. Here, in order to improve the disturbance rejection performance of a conventional photometer circuit based on a basic current-to-voltage converter connection, a novel circuit based on both positive and negative feedback compensations was designed. The photometer circuit designed in this paper is robust against disturbances on the photodiode parameters, and the results showed that the robust photometer circuit is superior to the nonrobust one. The results were satisfactory and showed the importance of applying robust control techniques to the design of photometer circuits.

Linear robust photometer circuit

In this paper, a linear photometer circuit based on robust feedback compensation is presented. Here, the photodiode was modelled as a dynamic system and its mathematical model was obtained from the well-known equivalent circuit for a photodiode reported in scientific literature. Next, in order to make the output of the system robust against uncertainties and the inevitable disturbances that corrupt the response of the photometer circuit, a robust feedback controller was designed. Finally, the robust photometer circuit presented in this paper was compared against a conventional photometer circuit based on a transimpedance amplifier. The results of comparing the aforementioned photometers showed that the photometer based on robust control techniques is superior to the one based on the conventional design. The linear robust photometer circuit presented in this paper was used for making measurements of light at 670 nm, its temperature coefficient was very low, and very high sensitivity and linearity characteristics were achieved.

Daylight availability: a poor predictor of depression in Iceland

Objectives. To test the hypothesis that the unexpectedly low prevalence of winter depression in Iceland is explained by Icelanders enjoying more daylight, during the winter months, than allocated to them by latitude.Methods. A conventional photometer was applied to measure illuminance on a horizontal surface at 64°8.8’ N and 21°55.8’ W every minute throughout the year. The illuminance thus measured was compared with computed illuminance, based on theoretical upper bounds.Results. Daylight availability proved to be, on average, 60% of the theoretical upper bounds derived using clear sky conditions. Snow cover did not, on average, cause a significant increase in daylight availability. Great variability was observed in illuminance from day to day, as well as within days.Conclusions. Average daylight availability does not explain the lower than expected prevalence of winter depression in Iceland. The great variability in illuminance might, however, affect the expression of winter depression, as could daylight quality and genetic factors. (Int J Circumpolar Health 2004; 63(3):267–276)

Computer assisted determination of ATP in environmental and food samples by bioluminescent assay: comparison of algorithms

When the bioluminescent assay (BLA) for the determination of adenosine triphosphate (ATP) in environmental and food samples is performed by conventional photometers, a computing procedure is necessary to exclude the mixing time of reagents from the global time of the reaction because it produces a poor analytical precision [M. Mecozzi, A. Amici, G. Visco, Fres. J. Anal. Chem. 357 (1997) 747–751]. In this paper three automated procedures for correcting this interference were tested and compared with illustrate their advantages and drawbacks. The three techniques were the robust exponential regression and the outliers detection method (RER), the smoothing technique of Savitzky-Golay (SSG) and the smoothing technique of Kalman Filter (SKF). RER and SSG were found to be more effective than SKF in minimizing the effect of noise produced by the mixing of reagents. In addition, the application of computing procedures such as RER and SSG allow to improve the detection limit in the BLA performed by conventional photometers.

The use of statistical properties of transmission signals for particle characterization

AbstractThe measurement of transmission is an often used measuring principle in technology. The evaluation algorithms of fluctuating transmission signals are well known in the case of single particle measurement. By evaluating fluctuating transmission signals the particle characterization is also possible at high particle concentrations (0.01 to 30 vol.‐%). In comparison with conventional photometers a significant gain of information can be received. Fluctuating signals are caused by the statistical probability of a limited number of particles being present in a defined measuring volume. The evaluation of such signals allows the determination of particle concentration, particle size of monodisperse particles (extinction diameter) and information about structure of agglomerates independent from each other. Mathematical fundamentals and practical ways to measure these parameters are shown. Experimental results are examplarily presented for monodisperse, polydisperse and agglomerated suspensions.

Sun photometry using photodiode open circuit voltage measurements

A simple technique is explored in which the open circuit voltage of a photodiode is measured using a simple digital multimeter to monitor the solar irradiance and atmospheric optical depths in three spectral bands. The advantage of this technique is that the photometer only consists of an optical interference filter, photodiode, and a measuring digital multimeter, while the electronics circuitry otherwise needed in a conventional photometer is avoided. This makes the system very simple, cost effective, and versatile for even nonprofessionals to handle.

A sensitive kinetic assay of serum albumin based on its enzyme-like hydrolytic activity, using a new chromogenic and fluorogenic substrate

A new albumin assay, based on the unusual enzyme-like activity of the protein that promotes hydrolysis of ester bonds in fatty acid arylesters was designed for clinical routine use. The substrate introduced shows improved analytical wavelengths and is suitable for both photometric and fluorimetric assay. Experiments have been performed with a conventional photometer, a fluorimeter and a Cobas Fara autoanalyzer. Detection limits are as low as 10 μg/ml photometrically and 20 ng/ml fluorimetricaly. The method provides a sensitive quantitative determination of even minute amounts of albumin in liquid solution, and a simple semiquantitative test may be performed by fixing the dye on a test strip which then is immersed into a sample solution and observing the development of yellow color intensity.

Determination of pH, conductivity, residual chlorine and ammonium and nitrite lons in water with an unsegmented flow configuration

A flow injection configuration is proposed for the determination of five parameters (pH, conductivity, residual chlorine, ammonium and nitrite) of interest in the control of water quality. The system includes three different detectors (potentiometric, conductimetric and photometric) suitably positioned in a reversed flow injection configuration. Conductivity and pH are monitored continuously and the other three parameters are determined by sequential injection of conventional photometric reagents, for which a conventional photometer or diode array photodetector can be used.

A HIGH-SPEED, DUAL-CCD IMAGING PHOTOMETER.

ABSTRACT The SNAPSHOT is a high-speed, dual-CCD imaging photometer, with special capability for occultation observations. It is capable of recording occultation light curves in the presence of bright, nonuniform background illumination, such as occultations of stars by Saturn's rings or by comets. Such events are difficult or impossible to observe with conventional photometers. The fundamental idea that makes high time-resolution observations possible is to reduce the data rate by digitizing only those pixels in subframes containing the objects of interest.

A method for assaying of .ALPHA.-glucosidase and .ALPHA.-amylase using laccase.

Laccase from Polyporus versicolor was found to develop a strong blue or red color with phenol in the presence of coupling compounds such as 2, 6-dibromo-4-aminophenol or 4-aminoantipyrine. Based on this phenomenon, concentrations of phenol (0.05-0.4 HIM) could be determined from the density of the color developed with laccase. Thus, assay methods for α-glucosidase and α-amylase were designed. α-Glucosidase (0.02-0.2 units) hydrolyzed phenyl α-glucoside and the phenol released was converted to a colored substance by laccase. Human α-amylase could also be determined using phenyl maltotetraoside or pheny maltopentaoside as the substrate. The phenyl maltooligosaccharide was hydrolyzed to phenol and glucose by the combined action of α-amylase and α-glucosidase, and the resultant phenol was assayed by the same method as described above. The proposed method may be used in conjunction with a conventional photometer, because the color developed is reddish or blue.

A spectrophotometric method for the determination of monoglyceride hydrolase.

A monoglyceride hydrolase assay is introduced in which the activity of the enzyme is determined by the use of coupled enzymatic reactions. Measurements are easy to perform on a conventional photometer; they are specific, precise and show good reproducibility.

The influence of photometer design on optical-conformational changes

When cells and large subcellular structures suffer a change in volume or internal structure, their light-scattering properties are normally altered. These optical-conformation changes are potential sources of information about conformation and processes which alter it. Classical light-scattering theory for spherical particles is used to determine how the transmittance or extinction of a cell suspension should respond when such a conformational change occurs and the measurements are made with a conventional photometer. This extends an earlier study of transmittances measured with an “ideal” photometer. The photocell of an ideal instrument collects only the directly transmitted light. In a conventional instrument it also collects the light scattered at small angles, which is usually most of the scattered light. Extinction (optical density, absorbance) of suspensions of spherical cells was computed for several photometer designs. It is found that γ, the angle of acceptance of the photocell, has a significant influence on the extent and even the nature of the photometric response to a given conformational change. Earlier, it was shown that a decrease in cell volume or increase in internal structure will increase extinction for cells of many sizes. Now it is found that a large γ-value increases these effects. An approach to the interpretation of transmitted light fluxes in terms of theoretical predictions is outlined.