Use Of Neutral Density Filters Research Articles

Importance of spectrally invariant broadband attenuation of light in indoor photovoltaic characterization

Indoor photovoltaic (IPV) devices are poised to make a significant contribution to the proliferation of the “Internet of Things” (IoT). For the accurate intercomparison of IPVs (and, hence, to advance the rational development of the technology), lighting conditions representative of those in typical indoor settings must be created reproducibly. As indoor lighting is invariably broadband, this will typically require the use of optical attenuation to achieve varying irradiance conditions at the device under test location. However, most forms of optical attenuation will suffer from some degree of spectral dispersion, creating sources of uncertainty for key figures of merit, such as power conversion efficiency. In this work, we examine the contribution of the mode of optical attenuation to the accurate characterization of IPV systems. We discuss requirements for broadband light source attenuation for the accurate characterization of photovoltaic devices under indoor illumination and consider the importance of using suitable reference devices for light intensity calibration. Furthermore, we experimentally verify attenuation methods typically used, including power control of the light source itself, use of neutral density filters, and advanced attenuation based on tandem prism attenuators. Finally, spectral shape alteration-induced uncertainties in performance parameter determination of photovoltaic cells under indoor illumination are quantified for three common broadband light attenuation methods, where we found ∼2%, ∼6%, and up to ∼15% ambiguity in photovoltaic device efficiency when using LED power control, prism attenuators, and neutral density filter-based broadband light attenuation, respectively.

Commentary: The utility of automated pupillometry in retinal disorders.

Pupillary light reflex (PLR) remains an integral part of ocular examination providing an insight into the retinal, optic nerve, and brain stem functions. An altered PLR has significance in a multitude of ocular disorders such as third nerve palsies, optic neuritis, and central retinal vein occlusion.[123] A relative afferent pupillary defect (RAPD), detected by the swinging flashlight test, is indicative of an asymmetrical/unilateral retinal pathology or an optic nerve lesion and was first described by Levatin in 1959. Although the use of neutral density filters and standardized clinical grading has helped in quantifying RAPD, these methods remain limited by variable test conditions and observer bias.[4] The evaluation of RAPD with a swinging flashlight test is further hampered in patients with dark irides and small and/or poorly reacting pupils. Automated pupillometry helps in eliminating these barriers and provides an objective, standardized, and reproducible assessment of the pupillary function. In addition, the automated pupillometer is capable of assessing multiple variables, including pupillary size, constriction velocity, dilation velocity, and the latency of PLR. One of the earliest utilization of pupillometry in ophthalmology was described by Bloom et al.[3] in their study of central retinal vein occlusion. In eyes developing rubeosis, they observed a greater mean RAPD using neutral density filters, while infrared pupillometry revealed greater pupillary diameter and latency of constriction with a slower rate of pupillary constriction. They also concluded that because of the subjective nature of RAPD assessment, pupillometry was a more specific test generating a higher amount of measurable data and hence recommended its further development. Using pupillometry, Jain et al.[5] observed altered pupillary dynamics in the early stages of diabetic retinopathy and further observed that the dynamics deteriorated with the increasing severity of retinopathy. The importance of pupil assessment is heightened in neuro-ophthalmology cases to clinch the diagnosis. Kim et al.[1] evaluated the pupillary response in isolated third nerve palsy cases using an automated, infrared pupillometer. The ability of the automated pupillometer to quantify the pupillary response enabled them to calculate the pupillary constriction ratio, which they found to be highly specific for detecting third nerve palsy due to compressive etiologies. They were also able to distinguish microvascular ischemic third nerve palsy from those due to compressive lesions using digital pupillometry. Optic nerve disorders, including optic neuritis and nonarteritic anterior ischemic optic neuropathy (NAION), can significantly affect the PLR. Yoo et al.[2] observed a decreased pupillary constriction velocity, constriction ratio, and latency in acute optic neuritis and NAION using automated pupillometry. They also concluded that a delayed constriction latency and PLR recovery were features suggestive of optic neuritis over NAION. Although the role of PLR and automated pupillometer in age-related macular degeneration (ARMD) has been described in previous studies, the current study demonstrated its role in assessing macular lesions in choroidal neovascular membranes (CNVM) and also correlated the structural dimensions assessed on optical coherence tomography with RAPD scores.[678] Although the current study provides useful insights into the role of pupillometry in ARMD, the cross-sectional design does not address the role of evaluating the PLR in monitoring treatment response and disease progression, thus warranting further studies. Also, it would be interesting to evaluate the role of CNVM components such as subretinal fluid, intraretinal fluid, and subretinal hemorrhage on the RAPD scores. To conclude, automated pupillometry has a potential role to play in the monitoring of disease progression and response to therapy in ARMD and myriad other retinal disorders. Further studies are needed to expand the horizons about the role of this noninvasive, objective test for retinal pathologies. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.

Can Tinted Lenses Be Used to Manipulate Pupil Size and Visual Performance When Wearing Multifocal Contact Lenses?

BackgroundThe purpose of this study is to investigate the effect of wearing neutral density (ND) filters with different transmittance levels over multifocal contact lenses (MTF CLs) on pupil size, visual functions and the dynamic accommodative response under daylight conditions in early presbyopes.MethodsSeventeen individuals aged between 40 and 48 years (mean age 42.35±2.62 years) were recruited to participate in this study. This study involved a repeated-measures design with two within-subject factors: optical condition (which had five levels), and fixation distance (which had three levels). The five optical conditions were no correction (baseline), MTF CL wear, MTF CL wear + 0.3 ND filter (transmission [Tv]=48.38%), MTF CL wear + 0.6 ND filter (Tv=27.12%) and MTF CL wear + 0.9 ND filter (Tv=14.58%). The three fixation distances were 3 m, 40 cm and 20 cm. Outcome measures were pupil size, the measured accommodative response (optical aid + physiological accommodation), distance visual acuity (VA), near VA and contrast sensitivity (CS).ResultsThere was no effect of optical condition on the accommodative response; however, there was a significant effect of fixation distance. (Accommodative response was 0.44±0.29, 1.83±0.37 and 4.03±0.46 D for fixation distances of 3 m, 40 cm and 20 cm, respectively; p<0.05.) There was a significant effect of optical condition (p<0.05) and of fixation distance on pupil size variation (5.13±0.90 mm for 3 m, 4.71±0.92 mm for 40 cm and 4.11±1.04 mm for 20 cm; p<0.05). Optical condition had a significant effect on distance VA, near VA and CS (p<0.05). Compared to the reduction in distance VA, near VA was relatively small (two-letter reduction with 0.9 ND) and unlikely to be clinically significant.ConclusionThis study demonstrated that in a group of adults with early presbyopia, the use of ND filters enlarged pupil size. However, the combination of enlarged pupils and MTF CL did not improve distance vision, and if transmittance was reduced by 50% it resulted in decrements in vision and CS. MTF CL designs which incorporate tints, or tints that vary in darkness in response to ultraviolet exposure, should consider these findings.

High Temperature Calibration of Thermal Imagers for Infrared Measurements on Military Platforms

&lt;p&gt;Calibration of thermal imaging system is not a straight forward process and hence manufacturers suggest re-calibration at factory itself. However, it is time consuming and expensive. A few research papers refer various approaches to perform low temperature calibration considering the wide requirement of low temperature measurements (typically less than 150 °C). However, no reference is available in open literature about high temperature calibration of thermal imagers. Hence, the possibility of high temperature calibration of thermal imaging systems has been explored using high temperature blackbody sources available at laboratory. With the use of neutral density filters, calibration has been performed in mid-wave (3.7 μm - 4.8 μm) and long-wave (7.7 μm - 9.5 μm) bands of imagers for IR measurements. The developed calibration has also been tested for field measurements.&lt;/p&gt;

Use of fluorescence ratio imaging for intracellular pH determination of individual bacterial cells in mixed cultures.

The development of a rapid method for measuring intracellular pH (pHi) in single bacterial cells is described. Lactobacillus delbrueckii subsp. bulgaricus and Listeria innocua were used as test organisms. The method is based upon fluorescence microscopy and ratio imaging of cells stained with carboxyfluorescein succinimidyl ester. After staining, the bacteria were immobilized on a membrane filter and transferred to a closed perfusion chamber, allowing control of the cell environment during analysis. The set-up was optimized with regard to the use of neutral-density filters and background subtraction, for determining the excitation ratio 490 nm/435 nm (R490/435) independent of the excitation light intensity, and to reduce photobleaching. This allowed for time-lapse studies with multiple exposures. To study the pHi of Lb. delbrueckii subsp. bulgaricus and L. innocua in response to different extracellular pH (pHex) values, an in vivo calibration curve was constructed in the pHi range 5.0-8.5. Distinct differences between the two cultures were observed. L. innocua maintained a near-neutral pHi almost independently of pHex (5.0-8.0), whereas the pHi of Lb. delbrueckii subsp. bulgaricus decreased with decreasing pHex. In pure and mixed cultures at pHex 5.0, the pHi values of Lb. delbrueckii subsp. bulgaricus and L. innocua were 6.1 +/- 0.2 and 7.5 +/- 0.2, respectively. This difference in pHi may explain how Lb. delbrueckii subsp. bulgaricus obtains a competitive advantage over L. innocua at low pHex.

The Relative Afferent Pupillary Defect and a Novel Method of Fusion Recovery With the Worth 4-Dot Test

Objective: To examine the relation of the relative afferent pupillary defect and commonly used clinical tests of visual cortex binocular cell activity, namely, fusion and stereopsis. Methods: Sixty-seven subjects with neuroophthalmologic disorders underwent measurement of relative afferent pupillary defect and assessment of binocular sensory status by fusion on the Worth 4-dot test and stereopsis on the Titmus stereo test. Recovery of fusion on the Worth 4-dot test and improvement of stereopsis were tested by placing increasing neutral density filters in front of the eye that did not have the afferent pupillary defect. Results: Recovery of fusion on the Worth 4-dot test occurred with use of neutral density filters (Worth 4-dot neutralization test). No improvement of stereopsis was observed. A significant positive association was identified between the measured afferent pupillary defect and the measured log filter required for fusion (r=.83,P Conclusions: The relative afferent pupillary defect is a dynamic process that results from an imbalance of brightness sensitivity between the two eyes. Altering the latency (timing) and amplitude of the light stimuli by use of neutral density filters can restore fusion on the Worth 4-dot neutralization test but does not alter stereopsis. The Worth 4-dot neutralization test may be a useful adjunct in the assessment of visual dysfunction.

Differential effects of luminance and contrast on acuity thresholds across the visual field

Purpose: To investigate the effects of contrast and luminance on acuity thresholds across the visual field. This may shed some light on the important question of why some visual thresholds change only slowly as a function of eccentricity, whereas others fall off extremely quickly.Methods: Resolution thresholds for Gabor patches were measured in the nasal visual field using a modified yes/no staircase procedure. The effect of contrast was examined by changing the physical contrast of the Gabor stimuli between the values of 3.125 and 100%. The effect of luminance was investigated using high contrast Gabor stimuli but varying luminance over 2.7 log units with the use of neutral density filters. Natural pupils were used throughout.Results: The variation in resolution thresholds as a function of eccentricity was well described by the equation T = T0/[+(E/E2)], where T represents threshold, T0 threshold at the fovea, E is eccentricity and E2 is a parameter which describes the rate of decline in performance, representing the eccentricity at which the foveal resolution threshold halves. Changes in contrast resulted in the same logarithmic change in resolution threshold at all eccentricities, leaving the E2 value unchanged. Thresholds were proportional to the logarithm of contrast, and transforming the data in this way accounted for 98% of the variance in the eccentricity and contrast dependent data. Variations in luminance produced quite different effects, with E2 becoming significantly greater as luminance was reduced. At all eccentricities, resolution thresholds were proportional to the logarithm of retinal illuminance, but the gradient of this relationship changed markedly as a function of eccentricity, becoming close to zero at the higher eccentricities studied.Conclusions: The differential effects of contrast and luminance on acuity thresholds can be understood in terms of a pyramidal model of early vision in which reductions in suprathreshold contrast affect the signal by the same amount in all early visual filters, whereas reductions in luminance have a selective effect on smaller visual filters which are more susceptible to quantal noise.

The relative afferent pupillary defect and a novel method of fusion recovery with the Worth 4-dot test.

To examine the relation of the relative afferent pupillary defect and commonly used clinical tests of visual cortex binocular cell activity, namely, fusion and stereopsis. Sixty-seven subjects with neuro-ophthalmologic disorders underwent measurement of relative afferent pupillary defect and assessment of binocular sensory status by fusion on the Worth 4-dot test and stereopsis on the Titmus stereo test. Recovery of fusion on the Worth 4-dot test and improvement of stereopsis were tested by placing increasing neutral density filters in front of the eye that did not have the afferent pupillary defect. Recovery of fusion on the Worth 4-dot test occurred with use of neutral density filters (Worth 4-dot neutralization test). No improvement of stereopsis was observed. A significant positive association was identified between the measured afferent pupillary defect and the measured log filter required for fusion (r = .83, P < .001 by the Spearman rank correlation coefficient). In no case was a relative afferent pupillary defect observed when fusion without use of neutral density filters was present at baseline. For subjects with relative afferent pupillary defects, the measurements of the Worth 4-dot neutralization test were equal before and after pupillary dilation. The relative afferent pupillary defect is a dynamic process that results from an imbalance of brightness sensitivity between the two eyes. Altering the latency ("timing") and amplitude of the light stimuli by use of neutral density filters can restore fusion on the Worth 4-dot neutralization test but does not alter stereopsis. The Worth 4-dot neutralization test may be a useful adjunct in the assessment of visual dysfunction.

The Use of Crossed Polarized Filters in the Measurement of the Relative Afferent Pupillary Defect

We used crossed polarized neutral density filters to quantitate relative afferent pupillary defects. To prove reproducibility, the relative afferent pupillary defects of 20 patients were measured with this technique by two independent observers. There was no statistically significant difference between the two measurements. Relative afferent pupillary defects as low as 0.03 log unit were easily measured. These filters offer a convenient and reproducible technique that is more sensitive than the use of neutral density filters.

The influence of the spectral composition of irradiance on primary production in the Eastern Scheldt (The Netherlands)

The error inin vivo14C incubator measurements of primary production in the Eastern Scheldt when neutral density filters were used and the error obtained when no account was taken of the spectral changes in submarine irradiance that occur with increasing depth, were evaluated theoretically. By multiplying the photosynthetic action spectra of two marine algae by calculated irradiance in the euphotic layer using Kd and Kd(λ) respectively, the gross primary production P[Ed(400–700)] and P[Ed(λ)] was computed. In the green-brown waters of the Eastern Scheldt estuary the use of neutral density filters was sufficient to simulate the underwater light conditions. In clear waters it can cause an overestimation of the gross production.

Objective evaluation of binocular function using the pattern reversal visual evoked response. II. Effect of mean luminosity.

The effect of mean luminosity change on pattern reversal visual evoked response (VER), especially monocular VER, binocular VER and binocular summation, was studied. The mean luminosity level was changed with the use of neutral density filters. When mean luminosity level was decreased binocularly, binocular and monocular VER amplitudes decreased and binocular summation increased, reaching its peak at a luminosity of -0.3 log foot-lambert. When mean luminosity was changed monocularly and the interocular luminosity difference was larger than 0.6 log unit, the binocular VER became almost equal to or smaller than the monocular VER. In dim luminosity, the binocular system functioned better than the monocular system. Even a slight luminosity difference between the two eyes could disturb the binocular system.

Laser writing on silicon-metal bilayers for optical storage. II. Microscopic study

The nature of structural changes caused by laser writing on metal-silicon thin-film bilayers has been investigated by transmission electron microscopy and electron diffraction. Bilayers of amorphous Si and metals such as Au, Co, Pd, Pt, V, and Rh were reacted by laser writing for periods as long as 0.1 sec and as short as 5 nsec with varying powers by use of neutral density filters. Silicides formed by short laser pulses in bilayers on solid substrates are generally amorphous, while silicides formed on thin membrane substrates require less power for threshold writing and can be crystalline due to lower quench rates. Metallurgical reactions such as grain growth, interdiffusion, and compound formation, which normally require thermal anneals of up to 900 °C, have been observed to take place under laser writing with pulses as short as 5 nsec. Writing with excess power results in melting and hole formation as well as a sharp decrease in reflectivity. The maximum change of reflectivity can be obtained at proper (amorphous or crystalline) silicide formation. Effects of film composition and layer thickness on writing power and reflectivity change were investigated in Au-Si and Pd-Si. From all the systems investigated Rh-Si appears to be most promising due to its relatively low writing power and excellent archival properties.

Adaptation by hot spring phototrophs to reduced light intensities

Photosynthesis was measured by the 14C method on natural as well as low light adapted populations of Chloroflexus (a photosynthetic bacterium) and Synechococcus (a blue-green alga) from hot springs in Yellowstone National Park (Wyoming U.S.A.), to test the ability of these phototrophs to photosynthesize at a variety of light intensities. The herbicide 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU) was used to distinguish uptake of the blue-green alga from that of the photosynthetic bacterium, while measurements of chlorophyll a and bacteriochlorophyll c served to quantitate the standing crops of these organisms. Natural populations of Synechococcus were found to be slightly inhibited by full sunlight intensities (summer values can surpass 90000 Lux), whereas the Chloroflexus populations were not. Populations of both phototrophs subjected to reduced light intensities through the use of neutral density filters were found to adapt to low light, and then become severely inhibited by high light intensities. Adaptation to various light regimes may be an important ecological phenomenon to the survival of these hot spring phototrophs.