255 Spectrophotometric Properties of Commercial Blue-Blocking Lenses in Sunlight

Introduction Blue-blocking glasses are increasingly used as an intervention for jet-lag and other situations where an individual wishes to promote a “dark” signal despite the presence of ambient light. However, most studies on blue-blockers are done under controlled laboratory settings using emissions generated from electric light sources. The present study evaluated the performance of commercially available blue-blockers under daytime sunlight conditions. Methods A calibrated spectroradiometer (Ocean Insight), cosine corrector, optic fiber, and software package were used to measure the absolute irradiance (uW/cm^2/nm) available midday in a standardized location that received direct sunlight. Thirty-one commercially available blue-blockers were individually placed in front of the cosine corrector and intensity was measured and analyzed. Each lens was tested for its ability to block visible light, as well as light within the 440-530nm range. Lenses were evaluated individually and grouped by lens type: red-tinted lenses (RTL), orange-tinted lenses (ORL), orange-tinted lenses with blue reflectivity (OBL), brown-tinted lenses (BTL), yellow-tinted lenses (YTL), and clear lenses with blue reflectivity (RBL). Results Across the full spectrum, RTL blocked 66% of the light, OTL blocked 60%, OBL blocked 43%, BTL blocked 56%, YTL blocked 28%, and RBL blocked 20%. When the range was restricted to 440-530nm, RTL blocked 99%, OTL blocked 96%, OBL blocked 90%, BTL blocked 66%, YTL blocked 38%, and RBL blocked 17% of the light. Variation across lens types was significant for the full spectrum (one-way ANOVA, p < 0.0001) as well as the 440-530nm range (one-way ANOVA, p < 0.0001). Individual lenses showed variability in performance, though this variability was smaller than the between-group differences. Conclusion Under daylight conditions, red and orange lenses (RTL, OTL, and OBL) blocked at least 90% of the light in the 440-530nm range. Notably, RBL lenses restricted the most short-wavelength light as a proportion of the total light blocked. These data suggest that RTL, OTL, and OBL are effective at blocking the most circadian photosensitive components of daylight at the cost of reducing total illumination. Support (if any) R01MD011600, R01DA051321

Fast Dark Signal Measurements of SVOM VT CCDs Using the Vertical Gradient of Dark Field Images

This paper describes a fast technique for estimating the dark signals of the charge coupled devices (CCDs) of the visible telescope (VT) onboard the space multi-band variable object monitor (SVOM). It is based on the vertical gradient in the dark field images of the frame transfer CCDs. During the process of frame clear, exposure, frame transfer and readout, the characteristic of dark signal accumulation is analyzed firstly. Next, the linear fitting method is used to fit the signal level of the dark field image in the vertical direction, and the slope of the fitting line represents the dark signal factor. This technique only needs one dark field image and can be used for simple and efficient dark signal measurements of frame transfer CCDs. Besides, an experiment of detecting dark signals as a function of temperature based on the fast technique has been carried out. Making use of the Shockley-Hall-Read theory, two curve fitting formulas are adopted to the experimental results for VT Advanced Inverted Mode Operation (AIMO) CCD and VT Non-Inverted Mode Operation (NIMO) CCD respectively. The experimental results and the formulas are used to determine the optimal on-orbit cooling temperature of VT CCDs.

A method for measuring digital camera noise by automatic segmentation of a striped target

Currently, cameras are widely used in scientific, industrial and amateur tasks. Thus, one needs to be able to quickly evaluate characteristics and capabilities of a particular camera. A method for measuring noise components of the camera photosensor is proposed. It allows one to estimate shot noise, dark temporal noise, photo response non-uniformity and dark signal non-uniformity. For noise measurement, just two images of the same scene need to be registered. The scene consists of several stripes (quasihomogeneous regions). Then the images are processed by automatic signal segmentation. The performance and accuracy of the proposed method are higher than or equal to other fast methods. The experimental results obtained are similar to those derived using a time-consuming standard method within a measurement error.

Non-local terahertz photoconductivity in the topological phase of Hg1−xCdxTe

We report on observation of strong non-local photoconducitivity induced by terahertz laser pulses in non-zero magnetic field in heterostructures based on Hg1−xCdxTe films being in the topological phase. While the zero-field non-local photoconductivity is negligible, it is strongly enhanced in magnetic fields ~ 0.05 T resulting in appearance of an edge photocurrent that exceeds the respective dark signal by orders of magnitude. This photocurrent is chiral, and the chirality changes every time the magnetic field or the electric bias is reversed. Appearance of the non-local terahertz photoconductivity is attributed to features of the interface between the topological film and the trivial buffer.

Fixed Pattern Noise Reduction and Linearity Improvement in Time-Mode CMOS Image Sensors

In the paper, a digital clock stopping technique for gain and offset correction in time-mode analog-to-digital converters (ADCs) has been proposed. The technique is dedicated to imagers with massively parallel image acquisition working in the time mode where compensation of dark signal non-uniformity (DSNU) as well as photo-response non-uniformity (PRNU) is critical. Fixed pattern noise (FPN) reduction has been experimentally validated using 128-pixel CMOS imager. The reduction of the PRNU to about 0.5 LSB has been achieved. Linearity improvement technique has also been proposed, which allows for integral nonlinearity (INL) reduction to about 0.5 LSB. Measurements confirm the proposed approach.

Parasellar T2 dark sign on magnetic resonance imaging to differentiate lymphocytic hypophysitis from pituitary adenoma

Background: Pituitary adenomas are the most common sellar masses in adults with magnetic resonance imaging (MRI) being the imaging modality of choice. Inflammatory pituitary lesions such as lymphocytic hypophysitis (LH) can mimic pituitary macroadenoma on imaging and are often misdiagnosed as such. Although the imaging appearance on most of the sequences on MRI has similar findings, LH has a characteristic dark signal on T2 images (called dark T2 sign) which can be very helpful to reliably differentiate the two conditions. Case Description: A 68-year-old woman diagnosed with a “pituitary mass” on the MR study done at an outside facility was referred to our neurosurgery department. The case was discussed at our multidisciplinary tumor board, where the possibility of an inflammatory condition mimicking tumor was considered, given the very dark signal on T2-weighted sequences. Transsphenoidal endoscopic biopsy revealed a firm rubbery mass, which histopathology demonstrated fibrous connective tissue with inflammatory cells consistent with LH. Conclusion: Dark T2 signal on MR imaging can be very helpful in demarcating inflammatory pituitary conditions like LH from pituitary macroadenomas.