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Flicker Sensitivity in Normal Aging—Monocular Tests of Retinal Function at Photopic and Mesopic Light Levels
摘要： PURPOSE. Aging can affect many aspects of visual performance. In general, the effects become more significant in those older than 40 to 50 years, with increased intersubject variability and stronger dependence on ambient illumination. This study aimed to establish how healthy aging of the retina affects the detection of 15-Hz flicker under photopic and mesopic lighting. METHODS. We investigated 71 participants aged 20 to 75 years. Thresholds were measured for detection of 15-Hz flicker at the fovea (0°) and at an eccentricity of 4° in each of the four quadrants. The background luminance ranged from 0.6 to 60 cd/m2 and pupil size was measured continuously. Participants were excluded if they had signs/history of ocular disease, substantial interocular differences in flicker thresholds, or were unable to detect 100% flicker modulation in the high mesopic range. RESULTS. Mesopic and photopic flicker thresholds were used to calculate an index, the health of the retina index, to determine the limits of flicker sensitivity in healthy aging. Log flicker thresholds changed bilinearly with age; they remained stable until 40 to 50 years, with a linear decline with increasing age. This bilinear pattern of the change in flicker thresholds with age is consistent across photopic and mesopic light levels. CONCLUSIONS. The health of the retina index captures the lowest threshold, usually obtained under photopic conditions, as well as the loss of flicker sensitivity with decreasing light level. The established limits of healthy aging may benefit from future studies in patients with ocular hypertension and/or glaucoma that are known to experience loss of flicker sensitivity.
关键词： photopic,monocular vision,flicker,aging,mesopic
更新于2025-09-23 15:23:52
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Reliability of Heterochromatic Flicker Photometry in Measuring Macular Pigment Optical Density among Preadolescent Children
摘要： Macular pigment optical density (MPOD)—assessed using customized heterochromatic flicker photometry (cHFP)—is related to better cognition and brain lutein among adults. However, the reliability of MPOD assessed by cHFP has not been investigated in children. We assessed inter-session reliability of MPOD using modified cHFP. 7–10-year-olds (n = 66) underwent cHFP over 2 visits using 11 examiners. Reliability was also assessed in a subsample (n = 46) with only 2 examiners. Among all participants, there was no significant difference between the two sessions (p = 0.59—session 1: 0.61 ± 0.28; session 2: 0.62 ± 0.27). There was no significant difference in the MPOD of boys vs. girls (p = 0.56). There was a significant correlation between sessions (Y = 0.52x + 0.31; R2 = 0.29, p ≤ 0.005), with a reliability of 0.70 (Cronbach’s α). Among the subsample with 2 examiners, there was a significant correlation between sessions (Y = 0.54x + 0.31; R2 = 0.32, p < 0.005), with a reliability of 0.72 (Cronbach’s α). In conclusion, there is moderate reliability for modified cHFP to measure MPOD in preadolescents. These findings provide support for future studies aiming to conduct noninvasive assessments of retinal xanthophylls and study their association with cognition during childhood.
关键词： retinal lutein,heterochromatic flicker photometry,macular pigment optical density
更新于2025-09-23 15:22:29
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Response of Inner Retinal Oxygen Extraction Fraction to Light Flicker Under Normoxia and Hypoxia in Rat
摘要： PURPOSE. Oxygen extraction fraction (OEF), defined by the ratio of oxygen metabolism (MO2) to delivery (DO2), determines the level of compensation of MO2 by DO2. In the current study, we tested the hypothesis that inner retinal OEF remains unchanged during light flicker under systemic normoxia and hypoxia in rats due to the matching of MO2 and DO2. METHODS. Retinal vascular oxygen tension (PO2) measurements were obtained in 10 rats by phosphorescence lifetime imaging. Inner retinal OEF was derived from vascular PO2 based on Fick's principle. Measurements were obtained before and during light flicker under systemic normoxia and hypoxia. The effects of light flicker and systemic oxygenation on retinal vascular PO2 and OEF were determined by ANOVA. RESULTS. During light flicker, retinal venous PO2 decreased (P < 0.01, N = 10), while inner retinal OEF increased (P = 0.02). Under hypoxia, retinal arterial and venous PO2 decreased (P < 0.01), while OEF increased (P < 0.01). The interaction effect was not significant on OEF (P = 0.52), indicating the responses of OEF to light flicker were similar under normoxia and hypoxia. During light flicker, OEF increased from 0.46 ± 0.13 to 0.50 ± 0.11 under normoxia, while under hypoxia, OEF increased from 0.67 ± 0.16 to 0.74 ± 0.14. CONCLUSIONS. Inner retinal OEF increased during light flicker, indicating the relative change in DO2 is less than that in MO2 in rats under systemic normoxia and hypoxia. Inner retinal OEF is a potentially useful parameter for assessment of the relative changes of MO2 and DO2 under physiologic and pathologic conditions.
关键词： vascular oxygen tension,retina,oxygen extraction fraction,hypoxia,light flicker
更新于2025-09-23 15:22:29
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Cone Photoreceptor Dysfunction in Early-Stage Diabetic Retinopathy: Association Between the Activation Phase of Cone Phototransduction and the Flicker Electroretinogram
摘要： PURPOSE. To define the nature and extent of cone photoreceptor abnormalities in diabetic individuals who have mild or no retinopathy by assessing the activation phase of cone phototransduction and the flicker ERG in these individuals. METHODS. Light-adapted single-flash and flicker ERGs were recorded from 20 diabetic individuals who have no clinically apparent retinopathy (NDR), 20 diabetic individuals who have mild nonproliferative diabetic retinopathy (NPDR), and 20 nondiabetic, age-equivalent controls. A-waves elicited by flashes of different retinal illuminance were fit with a delayed Gaussian model to derive Rmp3 (maximum amplitude of the massed photoreceptor response) and S (phototransduction sensitivity). Fundamental amplitude and phase of ERGs elicited by full-field sinusoidal flicker were obtained across a frequency range of 6 to 100 Hz. RESULTS. ANVOA indicated that both diabetic groups had significant S losses compared with the controls, whereas mean Rmp3 did not differ significantly among the groups. ANOVA also indicated significantly reduced flicker ERG amplitude for frequencies ≥56 Hz for both diabetic groups compared with the controls. Flicker ERG timing (phase) did not differ significantly among the groups. Log Rmp3 + log S was significantly correlated with the patients’ high-frequency (62.5 Hz) flicker ERG amplitude loss (r = 0.69, P < 0.001). CONCLUSIONS. The delayed Gaussian a-wave model is useful for characterizing abnormalities in the activation phase of cone phototransduction and can help explain flicker ERG abnormalities in early-stage diabetic retinopathy. Reduced cone sensitivity and attenuated high-frequency flicker ERGs provide evidence for impaired cone function in these individuals.
关键词： electroretinogram,diabetic retinopathy,flicker electroretinogram,photoreceptors,a-wave
更新于2025-09-23 15:22:29
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Flicker Limit Compliance Assessment in the Presence of Background Disturbances
摘要： Assessing voltage fluctuations in the power system is necessary to prevent negative impacts to customers and the connected equipment. A flickermeter can be used to measure a flicker severity level that is based on the total voltage fluctuation present at a measurement point. The flickermeter can only assess the total flicker level at the measurement point; it cannot identify any individual network user’s contribution. For the purposes of limit compliance assessment, it is essential to have the ability to determine each user’s contribution. A measurement algorithm for accomplishing this task is presented in this paper. The algorithm is based on using measured voltages and user currents to determine the user complex power, and from the complex power and an online estimate of the network impedance, estimate the voltage fluctuation that the user would produce, if acting alone, at the measurement point. These estimated voltage fluctuations are used as inputs to the flickermeter so that the resultant flicker severity value reflects only the contribution of the individual user. Fourteen weeks of field test results are correlated with user demand data to demonstrate the effectiveness of the approach, and the traditional concepts of weekly percentiles, flicker summation, and background flicker are employed to validate the results.
关键词： power quality,RMS flicker measurement,voltage fluctuations,flicker discriminator,Flickermeter
更新于2025-09-23 15:21:21
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[IEEE 2019 Compound Semiconductor Week (CSW) - Nara, Japan (2019.5.19-2019.5.23)] 2019 Compound Semiconductor Week (CSW) - Mid-infrared photoresponse and robotic fabrication of graphene/h-BN van der Waals heterostructures
摘要： This paper introduces the parabolic variance (PVAR), a wavelet variance similar to the Allan variance (AVAR), based on the linear regression (LR) of phase data. The companion article arXiv:1506.05009 [physics.ins-det] details the Ω frequency counter, which implements the LR estimate. The PVAR combines the advantages of AVAR and modified AVAR (MVAR). PVAR is good for long-term analysis because the wavelet spans over 2τ, the same as the AVAR wavelet, and good for short-term analysis because the response to white and flicker PM is 1/τ3 and 1/τ2, the same as the MVAR. After setting the theoretical framework, we study the degrees of freedom and the confidence interval for the most common noise types. Then, we focus on the detection of a weak noise process at the transition—or corner—where a faster process rolls off. This new perspective raises the question of which variance detects the weak process with the shortest data record. Our simulations show that PVAR is a fortunate tradeoff. PVAR is superior to MVAR in all cases, exhibits the best ability to divide between fast noise phenomena (up to flicker FM), and is almost as good as AVAR for the detection of random walk and drift.
关键词： atomic frequency standard,frequency noise,measurement uncertainty,oscillator,frequency stability,Allan variance,flicker,phase noise
更新于2025-09-23 15:19:57
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A Procedure for Mitigating the Light Flicker in Office LED Lighting Caused by Voltage Fluctuations
摘要： Progress in the development of LED technologies has reached a state which justifies the replacement of lighting with traditional light sources, not only in new buildings but also in existing, older ones. One of such replacements was used as an example of a lighting flicker study presented in this paper. The results of initial measurements indicated that Rapid Voltage Changes (RVCs) are the cause of light flicker. The procedure was introduced and described in this paper to provide the necessary actions to mitigate the light flicker in LED lighting. In order to fulfil this task, the source of locally induced voltage fluctuations has to be identified. A method of identification was developed and a multi-function office printer was identified as the source of RVCs. Using a less sensitive LED driver, changing the connection point of the interfering device, and improving the electrical installation were considered as a set of possible solutions. Laboratory measurements have shown significant sensitivity of the LED driver to RVCs. The identified source of voltage disturbances was confirmed by a simulation of supply voltage variation in the presence of such device in Matlab Simulink with the use of digital flickermeter.
关键词： voltage fluctuations,light flicker,sensitivity of LED drivers,digital flickermeter,power control with zero voltage crossing
更新于2025-09-23 15:19:57
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Lighting flicker: a blind spot in indoor photovoltaic cell characterization
摘要： Pulse width modulation (PWM) driving is common in emerging solid-state or LED lighting. Unlike conventional lighting devices, the peak illumination intensity of a PWM-driven LED can be a hundredfold of average illumination intensity, causing strong lighting flicker. This work addresses the impact of the flicker on indoor amorphous Si (a-Si) photovoltaic cell performance. The power conversion efficiency of an amorphous silicon photovoltaic cell is found to be a function of not the average, but the peak illumination intensity. Indoor photovoltaic cells can thus seriously underperform under PWM-driven solid-state lighting when the peak illumination intensity is high enough to decrement photovoltaic cell performance.
关键词： Lighting flicker,power conversion efficiency,amorphous silicon,indoor photovoltaic cell,PWM-driven LED
更新于2025-09-23 15:19:57
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[IEEE 2018 International Conference and Exposition on Electrical And Power Engineering (EPE) - Iasi, Romania (2018.10.18-2018.10.19)] 2018 International Conference and Exposition on Electrical And Power Engineering (EPE) - Educational Platform for LCD Displays
摘要： The paper shows and describes a complex arrangement used for educational purpose within the learning process and curricula of students. The aims are to study and learn to control three LCD display types: one static drive LCD with 18 custom characters, a 4+1/2 digits static LCD with 7+1 segments and a 1/4 multiplex LCD (four commons) with both segments and custom characters. The platform consists of: circuit board, oscilloscope, programmer and computer. The circuit board was entirely designed and realized by the authors.
关键词： type A and B waveforms,bias,flicker,bias voltage,frame frequency,static drive,segments,internal memory registers,multiplex,commons,ghosting
更新于2025-09-19 17:15:36
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Shaped Accelerating Beams for Materials Processing
摘要： This paper introduces the parabolic variance (PVAR), a wavelet variance similar to the Allan variance (AVAR), based on the linear regression (LR) of phase data. The companion article arXiv:1506.05009 [physics.ins-det] details the Ω frequency counter, which implements the LR estimate. The PVAR combines the advantages of AVAR and modified AVAR (MVAR). PVAR is good for long-term analysis because the wavelet spans over 2τ, the same as the AVAR wavelet, and good for short-term analysis because the response to white and flicker PM is 1/τ3 and 1/τ2, the same as the MVAR. After setting the theoretical framework, we study the degrees of freedom and the confidence interval for the most common noise types. Then, we focus on the detection of a weak noise process at the transition—or corner—where a faster process rolls off. This new perspective raises the question of which variance detects the weak process with the shortest data record. Our simulations show that PVAR is a fortunate tradeoff. PVAR is superior to MVAR in all cases, exhibits the best ability to divide between fast noise phenomena (up to flicker FM), and is almost as good as AVAR for the detection of random walk and drift.
关键词： atomic frequency standard,frequency noise,measurement uncertainty,oscillator,frequency stability,Allan variance,flicker,phase noise
更新于2025-09-19 17:13:59