There is a need for accurate measurement of flashing lights for the proper maintenance of aircraft anticollision lights. A large variation in the measured intensities of anticollision lights has been a problem, and thus, NIST has undertaken the task to establish flashing-light photometric standards to provide calibration services in this area. A flashing-light photometric unit [lux second, (lx (DOT) s)] has been realized based on the NIST detector-based candela, using four standard photometers equipped with current integrators. Two different approaches have been taken to calibrate these standard photometers: one based on electrical calibration of the current integrator, and the other based on electronic pulsing of a steady-state photometric standard. The units realized using these two independent methods agreed to within 0.2%. The relative expanded uncertainty (k equals 2) of the standard photometers, in the measurement of the white xenon flash, is estimated to be 0.6%. The standard photometers are characterized for temporal response, linearity, and spectral responsivity, to be used for measurement of xenon flash sources of various waveforms and colors. Calibration services have been established at NIST for flashing-light photometers with white and red anticollision lights.
The quantities in LED measurements are discussed and their measurement conditions clarified. Necessity of standards created from the same type of LEDs is emphasized. New recommendations of the CIE organization are mentioned.
Calibration of sensitive, imaging type photometers, radiometers, or spectroradiometers for response generally requires a large area, uniformly radiating source that is accurately calibrated for luminance, radiance, or spectral radiance over relatively wide dynamic ranges. In many cases, automatic or computer control of the calibration source is desirable. This paper describes a series of automated integrating sphere calibration sources whose output can be precisely varied by either the accompanying electronic controller or an external computer. The calibration standard, which consists of a source module and an electronic controller, is designed such that it can be configured with integrating spheres having different diameters and various sized radiating ports. The luminance of the automated sphere sources can be varied from a maximum of 35,000 footlamberts to a minimum of 0.0001 footlamberts. The corresponding spectral radiance at 550 nm can be varied from 104 to 10-4 W/cm2 sr nm.
The performance of a novel compact large-area radiometric light source (CLARLS) has recently been demonstrated by the SeaWiFS (sea-viewing wide field-of-view sensor) quality monitor built for the SeaWiFS calibration and validation program. The SeaWiFS quality monitor (SQM) was successfully used as a calibration source onboard two trans-Atlantic cruises. The success of the CLARLS relies mostly on the uniformity of optical radiance it provides for sensor calibration. A theory to model the uniformity must account for the light scattering inside its light chamber. Here, such a model is proposed and the results of the numerical simulation are discussed.
The unique characteristics of the different types of retroreflective materials and devices used in the transportation field, require specialized designs of optical systems to accurately measure their properties. Various instruments are available to measure the retroreflective characteristics both in the laboratory and in the field. Certain parameters, such as aperture angles and the tolerances on observation angle and entrance angles must be considered when designing such systems or large inaccuracies will occur. Specific differences in the properties of the retroreflectors require instruments that resolve those differences. Geometry of measurement is an important factor in the instrument design. Examples of the light distribution returned from these retroreflectors and the corresponding measurement instrumentation are shown.
Displays providing NVIS compatibility must meet exacting standards. Instruments to test these devices must also perform to set minimum requirements, given in MIL-L-85762A appendix B. Traditionally, these requirements have been difficult to achieve in practice, and then only by compromising measurement conditions. A combination of new technology and application- oriented optimization of the spectroradiometer has led to recent revolutionary changes in NVIS measurement instrumentation. The optimizations possible, the mechanisms of achieving these optimizations, and the impact of any differences on measurements are discussed for two commercial instruments.
The complete and accurate colorimetric characterization of fluorescent materials requires the use of a 'bispectrometer;' a two-monochromator instrument designed to provide a two- dimensional matrix of bispectral radiance factor values for any given sample. This paper presents the general principles of operation, and a definition of the properties measured by such an instrument; expressing the actual physical quantities measured as an approximation to corresponding theoretical quantities. Approaches to calibration are outlined, with particular attention to the need for separation of reflected and luminescent components. Finally, this paper describes the calculations required to reduce the bispectral data produced by the instrument to more familiar colorimetric terms.
A new approach to imaging colorimeter design has been demonstrated. This approach is based on the concept of spectrally adaptive filtering of images, which permits adjustment of the overall response of the system for measuring color coordinates to fit one of three color matching functions and to change its spectral response rapidly. The experiments conducted demonstrated high spatial resolution -- 512 by 512 pixels or more (for nonpixelated objects), capability of performing color coordinate measurements of an entire image in 1/30 second, and high measurement accuracy.
A high-pressure laser-guided gas-embedded plasma pinchlamp is described for the generation of intense UV radiation. It has been configured to optimize energy transfer from the storage PFN. The output energy peaks within the spectral range 150 - 250 nm with a pulsed power of 20 MW at 10 Hz. The device employs a working gas of argon at 3 AMAGAT and has a pulsewidth of 20 microseconds. The results of exploratory surface modification experiments with the pinchlamp are reported. These include the destruction of chemical warfare agent simulants, asbestos, petroleum, and insecticides on surfaces as well as semiconductor annealing. In addition it was determined that various aircraft coatings are able to be removed from aluminum and composite substrates. These coatings included primers, top coats, and anti-erosion materials. This pinchlamp technology potentially fills a performance gap in the hard ultraviolet between flashlamps and lasers. On the one hand it offers a peak power and brightness comparable to parameters customarily associated with laser technology. On the other hand it possesses the efficiency, simplicity, and scalability often encountered with conventional flashlamp systems.
A principal function of a lamp is to produce light output with designated spectra, intensity, and/or geometric radiation patterns. The function of a precision performance lamp is to go beyond these parameters and into the precision repeatability of performance. All lamps are not equal. There are a variety of incandescent lamps, from the vacuum incandescent indictor lamp to the precision lamp of a blood analyzer. In the past the definition of a precision lamp was described in terms of wattage, light center length (LCL), filament position, and/or spot alignment. This paper presents a new view of precision lamps through the discussion of a new segment of lamp design, which we term precision performance lamps. The definition of precision performance lamps will include (must include) the factors of a precision lamp. But what makes a precision lamp a precision performance lamp is the manner in which the design factors of amperage, mscp (mean spherical candlepower), efficacy (lumens/watt), life, not considered individually but rather considered collectively. There is a statistical bias in a precision performance lamp for each of these factors; taken individually and as a whole. When properly considered the results can be dramatic to the system design engineer, system production manage and the system end-user. It can be shown that for the lamp user, the use of precision performance lamps can translate to: (1) ease of system design, (2) simplification of electronics, (3) superior signal to noise ratios, (4) higher manufacturing yields, (5) lower system costs, (6) better product performance. The factors mentioned above are described along with their interdependent relationships. It is statistically shown how the benefits listed above are achievable. Examples are provided to illustrate how proper attention to precision performance lamp characteristics actually aid in system product design and manufacturing to build and market more, market acceptable product products in the industrial, medical and consumer markets.
A technology of spectrally adaptive light filtering has been demonstrated, which allows changing the transmission curve of an optical filter in an octave-wide spectral interval with the kilohertz rate under full computer control. This technology utilizes the unique capability of acousto-optic tunable filters to transmit light in several spectral intervals simultaneously, driven by radio signals with complex spectra. A computer algorithm to synthesize the driving signal for an arbitrary given spectral transmission curve was developed. This algorithm has been used for various applications of this developed technology in the visible, SWIR, and MWIR spectral intervals.
This paper examines the possibility of tuning the lamp spectrum to compensate for color distortions in fiber optic lighting systems. Because most optical fibers have strong absorption in the blue and red wavelength regions, white light entering and propagating down an optical fiber suffers varied amounts of attenuation as a function of wavelength. As a result, the light exiting the optical fiber has a greenish tint that the lighting design community considers undesirable in interior lighting applications. HID lamps are commonly used for the light source in this industry. Certain classes of HID lamps tend to shift in color when their operating position or the input voltage to the lamp is changed. An experimental study is being conducted to characterize the color shift properties of a small HID lamp as a function of tilt and input voltage. The study also examines the possibility of exploiting this color shift to compensate for the color distortions caused by optical fibers. The details of the experiment and the results are presented in this manuscript.
A near-field modeling technique was applied to modeling of a halogen extended light source. The modeling was performed to create a continuous set of rays which can then be used in raytracing for the purpose of designing a reflector. The near- field modeling was implemented by acquiring a series of images of the source using CCD camera with wide-angle lens focused at infinity. Optical ray model, which involved geometrical and ray modeling of the source to match its measured luminous intensity distribution, was also developed. Luminous intensity distribution as well as illuminance pattern from a reflector/source combination, calculated using near-field and optical ray models, were compared. It is demonstrated, in this paper, that near-field modeling technique has several advantages over the optical ray modeling technique when used for computer design of reflectors.
Perhaps the most significant factor impacting the accuracy of software for the design of illumination optics is the proper characterization of the light source. Techniques used in the past have employed a simplified geometry to model the emitting element of the lamp along with an intensity distribution which has been measured at some fixed distance. This produced major inaccuracies in the prediction of the optical performance of complicated systems. The authors have been active for several years in developing improved techniques for lamp characterization. It is the intent of this paper to describe the aspects of lamp modeling which we have found to be important. These factors include the use of 'far-field' and 'near-field' photometry, the spatial variation of luminance over the lamp, and re-emission of radiation incident on the lamp. The most difficult light sources to model accurately are high intensity discharge sources. Methods are discussed for the solid modeling of such light sources by the use of luminance and intensity data. Instrumentation for the collection of these data is desired.
The knowledge of the true fog level of the exposed and developed photography emulsion is necessary both for correct plotting of the characteristic curve and for accurate determination of the exposing light intensity distribution. It is suggested to calculate the function S equals lg(10D-Df - 1), where S is the modified Seidel function, D are the measured densities and Df is the fog density. The value of Df at which S versus logarithm of exposure shows a linear form, is the true fog density. This linear dependence is an additional criterion that allows one to judge the correctness of the fog level evaluation and to distinguish the fog from a uniform background.
It has been shown that with correctly defined fog level of the exposed and developed photographic emulsion the characteristic curve of photographic emulsion from the linear region to the low exposure one may be linearized by using the Seidel function. For characteristic curve fitting one should know three approximation constants which may be calculated by three reference points on the image represented by three densities at three different exposures. Different exposures may be realized by different intensities of illuminating light at the same exposure time as well as by taking three images of the same object at different exposure times.
The low characteristic curve (CC) gradient of the exposed and developed photographic emulsion (PE) near fog imposes certain restrictions on the photographic photometry accuracy and the weak object detection threshold. The conventional model of PE, where the effective absorption density of a certain PE area is used as an exposure measure, has been exhausted. With such a model photometry accuracy and detection capability of PE can be enhanced only by the development of new types of PE. The properties of existing PE may be improved if the conventional exposure measure is complemented by a new PE parameter which can be measured simultaneously with the density. A new PE model is offered in which in addition to the density of a certain PE area, the intensity of the light scattered by the developed PE grains of the same area is measured. It has been shown that the scattered light intensity measured within a sufficient aperture and corrected for PE grain absorption can serve as a low exposure measure and demonstrates a sufficient gradient of the new CC where the conventional CC has a gradient close to zero.
A new design method of the dichroic mirrors is proposed for color separation/composition in 3-LCD projection systems. In this method, the design parameters were optimized by maximizing the volume of the reproducible color gamut in a CIELUV uniform color space for 2 typical viewing conditions.
A rugged, portable Nd:YAG standard has been developed to calibrate Navy laser detectors or systems from 0.05 mj to 120 mj at 1064 nm. The Laser Transmitter Support Standard was designed as a versatile calibration standard for accurate energy and pulsewidth measurements. It has excellent polarization ratio characteristics and can be configured to perform boresight testing. The Class IV laser system was designed to enable eye safe calibrations. The prototype standard has been used in a range of field applications including the calibration of laser transmitter test sets. The paper explains the performance specifications, capabilities, and uses of the LTSS-1064, as well as the polarization, noise, portability, and safety issues that were overcome.