Reference Light Source Research Articles

Spectrophotometer Calibration by a Double Integrating Sphere Reference Light Source and Display Panel Measurement Using Dark Sphere

We succeeded to develop a reference light source in the range of very low luminance using a double integrating sphere system, and calibrated a commercial spectrophotometer below 1 × 10-5cd/m2 levels, which is 1/100 lower than the specified limit for measurement. And we improved measurements in the ultra low luminance range of displays using the calibrated commercial spectrophotometer and a dark sphere to suppress the influence of the surround.

A colour harmony rendering index based on predictions of colour harmony impression

This study describes the development of a new measure intended to improve the description of light source colour quality. Previously, the authors have developed several colour harmony formulae to describe observers' impressions of colour harmony for two- and three-colour combinations seen under well-defined viewing conditions. One of the applications of these formulae is to quantify the distortion of colour harmony that can occur on changing from one light source to another. Based on the colour harmony predictions of these formulae for a sample set of colours seen under reference and test light sources a new light source colour quality metric, the `colour harmony rendering index', is defined. Two experiments were carried out to investigate the correlation between visual observations and this new colour quality metric.

Use of statistical checks as maintenance tools for TLD readers

Although the values of different parameters may remain within permissible limits during the operation of a thermoluminescent dosemeter (TLD) reader, certain effects can become apparent only when a long-term followup of these parameters is performed. In order to ensure an accurate and reliable operation of a TLD reader, the system characteristics must be monitored continuously. Long-term statistical checks of key system parameters may give a broader insight into the operational characteristics of the TLD reader and may help for proper maintenance of the system. The photomultipliers noise, the internal reference light source stability and the A to D reference voltage were found to be critical parameters, which have a major influence on the accuracy and stability of the system. A followup of these parameters for a period of about 10 y is presented, and some problems are seen to be reflected in the distributions.

Real-time gain correction method using a reference light for an area-parallel-type frame-transfer charge-coupled device with multi-output taps

The authors propose a technique for performing real-time correction of the gain nonuniformity at output taps in an area-parallel-type frame transfer CCD (FT-CCD) by incorporating a reference optical signal. This technique activates a reference light source every vertical blanking (V-blanking) period, during which time the image sensor is shielded from incident light, and uses that output signal level to automatically adjust the gain of each block. For this method, a color-separation prism with reference light sources has been developed. In addition, to obtain a reference signal from the reference light source emitting for about 11% of the V-blanking period, a new method of accumulating the electron signal generated by the reference light source is described for the CCD. The results of a camera experiment using an 8-million-pixel CCD are described, and the compensation accuracy of this method is discussed.

Stabilizing scintillation detector systems with pulsed LEDs: a method to derive the LED temperature from pulse height spectra

Photomultiplier tubes (PMTs) can be stabilized with light emitting diodes (LEDs) used as reference light sources. The LED is supplied with short voltage pulses that produce well-defined light portions if the LED temperature is kept constant. However, if the PMT must be operated in a wide temperature range, the LED light output is no longer a constant but becomes a function of the junction temperature. This problem can be solved at low expense by means of a new method. The LED is operated in two alternating pulse modes distinguished by the pulse voltage. The LED light output depends on the pulse voltage and, therefore, the PMT pulse height spectrum shows two distinct peaks. However, not only is the total amount of light L emitted per pulse but also the shape of the temperature dependence L(T) varies with the pulse voltage. The numerical ratio R of the peak positions corresponding to the two different LED modes is therefore a function of the LED temperature as well. Since it is a ratio, R is independent of the actual PMT gain but characterizes the LED junction temperature. Thus, the pulse height ratio of the different LED signals can serve as an LED thermometer. Moreover, measuring L and R at several temperature points covering the full operational range yields a calibration function L(R). With this knowledge, commercial off-the-shelf LED components can be used as precise reference light sources in a wide range of ambient temperatures

Monitoring the Variations in Spectral Sensitivity during the Calibration of a Light Source

While calibrating a light source against a reference light source, the spectrum of the latter often does not coincide with that of the calibrated source. This leads to the problem of considering variations in the shape of the photodetector's spectral sensitivity. A method to measure relative changes in the photodetector's spectral sensitivity is proposed. In the application of this method, no assumptions are made about the stability of the amplitudes of the sources' light flashes. In addition, it is not assumed that responses of the photodetectors are stable. The results from the experimental verification of this method are given.

Phase error measurement of an arrayed-waveguide grating in the 1.3-μm wavelength region by optical low coherence interferometry

This letter reports a method for generating transistor-transistor logic clock pulses at equal intervals of one quarter of the reference laser wavelength as the optical path difference between two arms of a Mach-Zehnder interferometer increases. With this technique, the phase error of an arrayed-waveguide grating operating in the 1.3-μm band can be measured precisely with optical low coherence interferometry using a tunable laser at 1.5 μm as the reference light source.

Calibration of the sensitivity of imaging atmospheric Cherenkov telescopes using a reference light source

Abstract The sensitivity of an Imaging Atmospheric Cherenkov telescope is calibrated by shining, from a distant pulsed monochromatic light source, a defined photon flux onto the mirror. The light pulse is captured and reconstructed by the telescope in an identical fashion as real Cherenkov light. The intensity of the calibration light pulse is monitored via a calibrated sensor at the telescope; in order to account for the lower sensitivity of this sensor compared to the Cherenkov telescope, an attenuator is inserted in the light source between the measurements with the calibrated sensor, and with the telescope. The resulting telescope sensitivities have errors of 10%, and compare well with other estimates of the sensitivity.

Spatially dynamic calibration of an eye-tracking system

ERICA is a personal-computer workstation developed to provide nonverbal, motor-disabled individuals with a means of communication and environmental control. The system employs computer vision to detect the user's approximate point of regard on a display screen and then invokes the menu option currently appearing at the corresponding screen coordinates. In this way, a severely handicapped user can run menu-driven applications with eye fixations as the only mode of input. This correspondence describes the design and testing of a spatially dynamic calibration for ERICA. The purpose of the new design is to improve the accuracy and precision of point-of-regard estimation by reducing the sensitivity of the system to head movement in the lateral plane (parallel to the display screen). The design introduces a second reference light source, which permits differentiation of head movement from eye rotation in the camera image. Symmetries in point-of-regard estimates for different fixed-head locations, which are observed by simulating the image response to eye and head motions, are exploited in the calibration model. The design is shown to provide accurate point-of-regard estimates in the presence of significant lateral head displacements while simultaneously improving overall estimation precision by approximately 85%.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

デジタル光学素子を用いた形状測定方法の研究 (第1報)

This paper describes a new noncontact optical method to measure a profile of a reflective object. One of the methods to reduce affects of disturbance light and changes of the object surface is to use the controllable active lighting system as the reference light source. The digital optical devices, an LED array and a plasma display are used in this method as an active light system that can be controlled by the computer system. The form of the reflecting surface that has large and complex curvatures is difficult to measure by image processing, because of difficulty to recognize the relations between lights and reflecting images. This method recognizes easily the relations between lights and reflecting images and reduced affects from disturbance light and changes of surfaces. The star form reflecting object of diameter about 100mm that had large and complex curvatures was measured by this system.

A compact low-radiance multichannel reference source of diffuse visible and near-infrared radiation for airglow studies

A description is given of a reference light source constructed for use with a three-channel airglow spectrometer. It uses the principle of the integrating sphere, to meet the requirements of compactness and portability, supplying approximately white light of low and uniform radiance and of selected intensity into each of three apertures of diameter about 100 mm.

A stabilized NE213 scintillator for neutron time-of-flight spectroscopy

A pulsed light emitting diode (LED) of constant light output is used as a reference light source to stabilize the amplification of a 4″ø × 2″ NE2213 scintillation detector against long term drifts, temperature and count rate variations. The detector pulse height has been kept constant for several days to within ±0.5% [±1.0%] for temperatures between (20±1)°C[(20±5)°C] and count rates up to 20 kHz. The LED is rigidly coupled to the scintillator cell. The whole stabilization system including two coupled regulation loops is housed in a 2 12 NIM case. The electronic circuitry is presented in principle and in detail, and detector test results are discussed.

A reference light source employing scintillations in air

A new type of reference light source utilising air as a scintillator is described. Investigations carried out with this type of light source, which is simple in construction, show that it can be used for routine checking of light detection systems employing photon counting or dc measuring systems.

Photometric measurement of retroreflection: a new calibration procedure

The problems involved in photometry of retroreflectors are considered: for example, low light levels, heterochromatic photometry, and critical effect of geometric parameters. In order to simulate practical use conditions the visibility of the retroreflector depends on the illumination received in normal driving situations at various distances and incidence angles from the headlamps of the following car and on the luminous itensity retroreflected in the direction of observation. The test apparatus consists of precise realisation of geometric parameters, adequate photometric components and practical calibration procedure with the highest accuracy. A new calibration technique, used at IEN, is here suggested. This requires one uncalibrated reference light source and two uncalibrated photo-detectors instead of calibrated light sources or calibrated photo-detectors as conventional procedures need.

Reference light source for luminance and illuminance photometry

The rationale for a constant source of both luminance and illuminance to check photometer calibration is discussed. The inexpensive construction of such a reference source is described, together with some performance data.

Bioluminescence from single bacterial cells exhibits no oscillation

Since the usual measurements of light emission from marine bacteria involve many (10(6)-10(10)) cells, the question has often been raised as to whether or not the individual cell's luminescence is truly continuous. To investigate this question, we assembled a sensitive photo-counting system with computerized data acquisition. Several luminous species were studied: Beneckea harveyi, Photobacterium belozerskii, P. fischeri, and P. leiognathi. Isolated single cells gave count rates ranging from 2 to 10 times the background, depending on the brightness of the strain and the state of induction. No flashes, bursts, or oscillations were evident from data collected in counting intervals of 100 ms, using both photo time-correction and power spectral analysis. Our algorithms could detect an oscillating component with an intensity as low as 0.3% of the average, as determined by the analysis of reference light sources. That photons are emitted randomly was further shown by the fact that the count distribution from the living cell closely matched that of a reference light source attenuated to the same average count rate.

A long term stable reference light source using LEDs for stabilization of scintillation spectrometers

This note reports on a reference light source using a green LED with a stabilized light output for photomultiplier gain stabilization systems. A stabilization system has been designed and constructed using a PIN-photodiode monitoring and stabilizing the light output of the light emitting diode. In measuring the LED light output per pulse an error signal is developed and fed back to the pulser unit flashing the LED. Thus, long-term instabilities of the LED light output, which are of the order of 0.1% per day, and its temperature dependence (about 0.5%/° C) are reduced to an overall stability of the system of 0.1% independent of time and temperature variations between 10°C and 35°C. This LED reference light source can be employed in all types of photomultiplier gain stabilization systems used according to the experimental requirements.

Ultraviolet Assessment of Artificial Daylight by Use of Fluorescent Metamers

The method developed in the authors' previouspaper is applied to assess ment various artificial daylights in the ultraviolet spectral range. Assessed results are compared with those of thecolor renderting property use of fluorescent samples foundin terstiege's and with those by the degree of fluorescence-excitation by Berger and Strocka. The assessment of color rendering property is significantly influenced by the difference in spectral power distribution between the test and the reference light source in the visible spectral range and is rejected as inadequate index for assessing the ultraviolet range of spectral power distributions of the artificial daylight. There is no correlation between two residual methods of assessment; the one by the degree of fluorescence-excitation and the other by use of fluorescent metamers proposed by the present authors. By inspecting the ultraviolet range of spectral power distributions of the tested light sources, it is discussed what can be detected by each of the methods. It is pointed out in the discussion that only onl, i, e, the method by the degree of fluorescence-excitation or the method by use of fluorescent metamers is insufficient and a combined treatment of both the methods is recommended for assessing the ultraviolet spectral range of artificial daylights.

Spectroscopic slope temperature measurements using a noncalibrated tungsten lamp as a reference light source

The spectroscopic slope method for temperature measurements requires the calibration of the spectrometer spectral response, unless the spectral lines or band components all occur in such a small wavelength interval that the response is constant. A calibrated tungsten lamp is generally used when a spectral response calibration is required. Accurately calibrated tungsten lamps are relatively expensive and generally do not have long term stability. To circumvent this problem, a method has been developed for which noncalibrated tungsten lamps may be used as reference light sources for calibrating the spectrometer wavelength response when the true tungsten filament temperature of the reference source is equal to the unknown source temperature. Then, a plot of the proper qualities vs the lower energy level of the spectral lines provides the source temperature. The absolute calibration of the tungsten lamp is not required.

A Remote-Position Analyzer with Electronic Output

A remote position measuring device with electrical coupling to a computer has been developed for use in the elementary-physics laboratory. Light from a moving object and a fixed-reference lamp is focused by a lens on a hollow, rotating drum with equally-spaced slits. The light passing through a slit is detected with a phototube. The time difference of amplified phototube signals from the object and reference-light sources is a measure of the position coordinate of the object at the time of the object signal. The model constructed has a precision of about 0.03 cm, better than a 3% differential linearity for a 40-cm field of view in the object plane and a sampling rate of 30 sec−1. The device can track more than one object simultaneously and has been successful in providing position samples for two colliding gliders on an air-track.