A LED based white light source (WLS) is designed and constructed to determine the color characteristics of the samples
having specular and diffuse reflectance properties at the standard measurement conditions of 0/45 and d/8. The light
source is composed of high power cool white and ultraviolet light emitting diodes (LEDs) which are operable in
adjustable current levels. In order to combine the light beams emerging from two LED sources, a 1x2 fiber optic
combiner is used. Optical characterizations of the light source designed and influences of several colorful LEDs called
Royal-Blue, Blue, Cyan, Green, Amber, Red-Orange and Red on spectrophotometric properties of the light source are
investigated.
The illuminance responsivity dependencies on spectral power distributions (SPDs) of different types of light sources are studied. In this work we used three types of calibrated photometers, one of which was home-made and two were commercial photometers. A monochromator-based facility was used to scan SPDs of light sources. The dependencies of spectral mismatch correction factors F(St,Ss) and the illuminance responsivities of photometers versus the SPDs of tungsten-filament incandescent, fluorescent, high-pressure sodium, and metal-halide light sources and white/colored light-emitting diodes are presented throughout this work.
In order to establish light emitting diode (LED) based spectrophotometric standard light source we used high-power Luxeon Star white LEDs having nominal electrical powers of 5W and 1W. Especially designed aluminum cooling block was used to protect LEDs from heating and to reduce heating effects on optical and electrical parameters. The chromaticity coordinate (CC) and correlated color temperature (CCT) properties of each LED were characterized by the measuring of spectral power distribution between 360 nm and 830 nm wavelength range. Then using spectral power distribution values and CIE color-matching functions at 2° observer, tristimulus values and CCs were calculated in both CIE-1931 and CIE-1960 spaces. CCTs then were calculated using computer interpolation method.
Refractive index knowledge is one of important parameter when physical properties of materials are investigated. It is also known that temperature variation and wavelength are also effect on the measurement results when materials are characterized. Therefore fast and accurate measurements are needed to measure especially refractive index properties of material. In order to cover this poverty we established we established a computer controlled an optical facility in National Metrology Institute of Turkey, based on laser beam displacement technique. Basic components of established facility are laser sources, sample holder, knife-edges and detectors. In order to compensate fluctuations arising from laser instability we used electro optic modulator that kept the intensity of lasers stable at around 10-5. A temperature controlled sample holder was used to measure temperature dependence of materials. The displacement of laser beam was determined using knife-edge, which moved using a computer controlled servomotor. The refractive index than was found
from displaced laser peak signal using designed trap detectors based on three single-element silicon photodiodes.
The luminous intensity unit and traceability in derived units of illuminance and luminance were realized using new detector-based approach at the National Metrology Institute of Turkey. Services in photometry were enlarged to perform high-level illuminance and luminance meter calibrations, namely at levels up to 5000 lx and 5000 cd/m2 by using the working standard photometer heads, precise apertures and integrating spheres on the 6 m long photometric bench. Working standart photometer heads which consist of a single silicon photodiode, V(λ)-corrected filter, precision aperture and a cosine corrected diffuser were calibrated for luminous responsivity in A/lx. For precision in the measurements, positions of illuminance meters and photometer heads are compared by using step motor controlled translation stages. The measurements are carried out at the color temperature of 2856 K and in the conditions where the inverse square law is applicable. The same photometer heads are used to measure luminance unit. The purpose of the work is to present established photometric systems and describe capability which is being applied at UME for the realization of calibrations of illuminance-meters and luminance-meters.
This work presents the progress made in primary level photometric measurements at the National Metrology Institute of Turkey (UME). A Cryogenic Radiometer (Oxford Instruments Radiox) was employed in the optics laboratory as an absolute primary standard. Temperature-controlled filter radiometer constructed from three-element silicon trap detector, band-pass filters and precision aperture. Filter radiometers were calibrated using the cryogenic radiometer at discrete laser wavelengths of vertically polarized tuneable Ar+, fixed He-Ne and Nd: YAG (with second harmonic) laser sources. Luminous intensity unit of candela was realized with an expanded uncertainty of 2.88x10-3 and photometric scale was re-established depending on this detector-based realization. Candela realization was performed on optical bench using traditional Osram Wi41/G type incandescent light source and an absolute filter radiometer. Other derived units of photometry that are luminous flux, illuminance, color temperature and luminance are derived from candela through various photometric measurements including some homemade devices of laboratory.
We will use InGaAs and Ge based reflection type trap detectors as a detecting element and lasers as light sources to realize the absolute power and responsivity scales in the near infrared region. The output of lasers should be stabilized in order to make measurements on the metrological level. Therefore, we have established a home made laser intensity stabilization optics in the laboratory. The intensity stability of infrared lasers was reached to a level of 5x10-5 with this system. We have employed a spatial filter, which consists of a 10X objective, a 25 μm pinhole and a Plano convex lens in order to generate a clean beam with the desired dimension Circular power distributions and Gaussian properties of the beams were analysed by using a CCD beam profiler.
An optical power scale is established at Ulusal Metroloji Enstitüsü (UME) using the helium-cooled primary-level electrical-substitution cryogenic radiometer. The scale is established at discrete laser wavelengths of vertically polarized tuneable Ar+, fixed He-Ne, and Nd:YAG (with second harmonic) laser sources. To increase measurement accuracy, laser intensities are stabilized to better than 0.009% using an electro-optical modulator. The spatial profiles of polarized laser beams are cleaned with a spatial filter. The optical power is measured using the static substitution method with an uncertainty of a few parts in 10–4. Repeatability of optical power measurements in the static substitution method, the measurement of window transmittance, and the measurement of power in a scattered beam are the most significant uncertainty components.
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