Adjustable light source for low light level with nearly constant correlated color temperature

Low light level (LLL) calibration becomes more and more important since the rapid growth of remote sensing. The spectral radiance at normal higher light levels can be calibrated with good accuracy, while LLL spectral radiance cannot. If an adjustable light source can be designed at nearly constant correlated color temperature (CCT) covering several orders of magnitude, low light level spectral radiance can be obtained with the help of a photodetector. Whether or not the spectral distribution of an integrating sphere based light source is nearly constant is investigated. By adjusting the diameter of the variable aperture between the integrating sphere and tungsten lamp, the spectral radiance can be varied over 6 orders of magnitude. However, the relative spectrum in the red region increases notably when the spectral radiance is decreased to 1/100000. If the spectral radiance is decreased further, the spectral difference can be more than 300% and CCT decreases more than 250 K. By using baffles and another integrating sphere, low light level radiation source at nearly constant spectral distribution is obtained. The variation of CCT is less than 50 K over 6 orders of magnitude.

Applicability of DIN 5036-3 to Transmittance Haze Measurement

This paper evaluates the applicability of the method described in DIN 5036-3 for transmittance haze measurement, theoretically and experimentally. It is shown that DIN 5036-3 is valid for total transmittance measurement. However, when applying to diffuse transmittance measurement, the measured value is lower than the theoretical one, resulting a lower value of calculated transmittance haze. The reflectance of the integrating sphere and collimation of the incident beam are the keys to achieve better agreement between theory and experiment. Further study is necessary to recommend solutions for the discovered issues.

PyPlr: A versatile, integrated system of hardware and software for researching the human pupillary light reflex

We introduce PyPlr—a versatile, integrated system of hardware and software to support a broad spectrum of research applications concerning the human pupillary light reflex (PLR). PyPlr is a custom Python library for integrating a research-grade video-based eye-tracker system with a light source and streamlining stimulus design, optimisation and delivery, device synchronisation, and extraction, cleaning, and analysis of pupil data. We additionally describe how full-field, homogenous stimulation of the retina can be realised with a low-cost integrating sphere that serves as an alternative to a more complex Maxwellian view setup. Users can integrate their own light source, but we provide full native software support for a high-end, commercial research-grade 10-primary light engine that offers advanced control over the temporal and spectral properties of light stimuli as well as spectral calibration utilities. Here, we describe the hardware and software in detail and demonstrate its capabilities with two example applications: (1) pupillometer-style measurement and parametrisation of the PLR to flashes of white light, and (2) comparing the post-illumination pupil response (PIPR) to flashes of long and short-wavelength light. The system holds promise for researchers who would favour a flexible approach to studying the PLR and the ability to employ a wide range of temporally and spectrally varying stimuli, including simple narrowband stimuli.

Predictive evaluation of multicomponent direct compress model tablets by integrating sphere UV-Vis spectroscopy and chemometrics

BACKGROUND: Control of the pharmaceutical manufacturing process and active pharmaceutical ingredients (API) is essential to product formulation and bioavailability. OBJECTIVE: The aim of this study is to predict tablet surface API concentration by chemometrics using integrating sphere UV-Vis spectroscopy, a non-destructive and contact-free measurement method. METHODS: Riboflavin, pyridoxine hydrochloride, dicalcium phosphate anhydrate, and magnesium stearate were mixed and ground with a mortar and pestle, and 100 mg samples were subjected to direct compression at a compaction pressure of 6 MPa at 7 mm diameter. The flat surface tablets were then analyzed by integrating sphere UV-Vis spectrometry. Standard normal variate (SNV) normalization and principal component analysis were applied to evaluate the measured spectral dataset. The spectral ranges were prepared at 300–800 nm and 500–700 nm with SNV normalization. Partial least squares (PLS) regression models were constructed to predict the API concentrations based on two previous datasets. RESULTS: The regression vector of constructed PLS regression models for each API was evaluated. API concentration prediction depends on riboflavin absorbance at 550 nm and the excipient dicalcium phosphate anhydrate. CONCLUSION: Integrating sphere UV-Vis spectrometry is a useful tool to process analytical technology.

ACCURATE MEASUREMENT OF ULTRAVIOLET LIGHT-EMITTING DIODES

We have developed a new calibration capability for 200 nm to 400 nm ultraviolet light-emitting diodes (UV LEDs) using a Type D gonio-spectroradiometer. The recently-introduced mean differential continuous pulse (M-DCP) method is used to overcome the measurement difficulty associated with the initial forward voltage, VF, anomaly of a UV LED, which makes it impossible to use VF to infer junction temperature, TJ, during pulsed operation. The new measurement facility was validated indirectly by comparing the measured total luminous flux of a white LED with that measured using the NIST’s 2.5 m absolute integrating sphere. The expanded calibration uncertainty for the total radiant flux is approximately 2 % to 3 % (k = 2) depending the wavelength of the UV LED.

Luster measurement of pearl by UV-Vis reflectance spectroscopy

Pearl is an organic gem with its unique color and luster. One of the factors determining the quality and price of pearl is the luster. The different luster of pearls could be related to the different phase structures such as aragonite, calcite and vaterite. Previously, a gloss meter has been developed to measure light specularly reflected at 45° to the surface normal. Six different visual criteria for measuring gloss have been determined. Luster, a type of gloss, was defined as the ratio of specularly reflected light and that diffusely reflected normal to the surface. In practice, luster may be interpreted as relative brightness of specularly and diffusely reflecting areas. Due to the roundness of pearl, we measured the luster of pearl samples by a portable UV-Vis spectrophotometer with an integrating sphere. The luster could be calculated from the difference of CIELAB lightness measured by SCI and SCE geometries.

Probing the interactions between dye molecules and metallic nanoparticles - Implications for surface enhanced spectroscopies

<p>The work in this thesis focuses on improving the understanding of two key aspects of the interaction between dye molecules and metallic nanoparticles, with particular relevance to Surface Enhanced Raman Spectroscopy (SERS). This is manifested from two main branches of experimental work; the first is concerned with improving the reproducibility of SERS sample preparation using colloidal solutions while the second focuses on directly measuring the absorption spectra of commonly used dye molecules on the surface of colloidal silver nanoparticles. In the first body of work of the thesis, a major step towards improving SERS in colloidal solutions is achieved by highlighting a crucial, but unnoticed possible source of error for such samples; by comparing average enhancement factor measurements on colloidal solutions prepared using different analyte (dye) dilution methods, it is shown that large dye dilution factors can cause extreme variations in nanoparticle coverage across the entire sample. This not only causes analyte-dependent enhancement factors (which is highly undesirable) but can also lead to false identification of single-molecule SERS experiments using the well established bi-analyte method. The errors associated with large dilution factors are interpreted as a competition between dye diffusion and adsorption kinetics. Time dependent fluorescence quenching measurements and finite element modelling (FEM) in COMOSL show that in any system where adsorption competes with diffusion, large dilution factors should be avoided. A simple protocol of half-half dilutions of analytes is proposed as a standard method to be adopted when preparing colloidal solutions for SERS to ensure uniform distribution of analytes is achieved. The second body of work is an experimental investigation of the modification of the energy levels of commonly used dye molecules adsorbed to spherical silver nanoparticles at sub-monolayer concentrations. Through the use of a novel integrating sphere setup, the absorption spectra of Rhodamine 6G, Nile Blue, Rhodamine 700 and Crystal Violet are successfully measured on the surface of silver colloids at ultra-low concentrations where dye-dye interactions are negligible. These results indicate that for most dyes, absorption pectra on the colloid surface are shifted and/or broadened with respect to the free dye in solution. In the most extreme case, a blue shift of almost 90 nm for Crystal Violet suggests a strong chemical interaction with the silver surface. A Mie theory shell model of dye-coated silver spheres is found to accurately reproduce the measured evolution of absorption spectra as the dye concentration on the colloid surface is increased but overestimates the enhancement in absorption, which is interpreted as a result of the adsorption geometry of dyes on the surface, not captured by the shell model. Finally, through careful wavelength dependent SERS measurements, the SERS Raman excitation profile of Crystal Violet is measured and shown to be closely linked to the modified absorbance as obtained in the integrating sphere setup. A standard optical transform model for computing the Raman excitation profile from the modified absorbance is applied and gives good agreement with the measured SERS data. These results represent a direct indication of chemical modifications of resonant molecules used in SERS studies.</p>