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At least 199 records · Page 11Linked to original sources
PubMed2002

Infant photometry: are mean adult isoluminance values a sufficient approximation to individual infant values?

Individual differences in isoluminance values were studied in infants and adults using a motion nulling paradigm. Two luminance-modulated sinusoidal grating components (spatial frequency=0.25 cpd, temporal frequency=5.6 Hz, speed=22.4 deg/s) were superimposed and moved in opposite directions across a color video screen. The contrasts of the two components were traded off to determine motion nulls. Two conditions were used: red/black vs. green/black, and red/black vs. blue/black grating components. An eye movement based response measure was used for infant subjects, and an average of 308 trials per infant were obtained. As observed in earlier studies, the mean motion null values for infants and adults were highly similar in each condition. The standard errors of motion null values for individual subjects were very small. Individual differences among infants were also small, and were clearly measurable only in the red/black vs. blue/black condition. The close similarity of mean null values, combined with the small individual differences among infants, supports the idea that under the right circumstances mean adult isoluminance values can be used as a sufficient approximation to individual infant isoluminance values in studies of infant color vision. These circumstances are discussed and evaluated in detail.

Adult↗
PubMed2002

Estimation of the hydrophobic fraction of dissolved organic matter in water samples using UV photometry.

In this study, we tested a simple and rapid method for the estimation of carbon in the hydrophobic fraction of dissolved organic matter (DOM) of different origin (spruce, pine, and beech litter) in soil water. The method is based on the fact that the hydrophobic fraction of DOM contains almost entirely the aromatic moieties of DOM. Thus, it showed a clearly distinct light absorption at 260 nm compared to the hydrophilic fraction. This light absorption was directly proportional to the concentration of the hydrophobic fraction. Moreover, it was independent of the concentration of the hydrophilic fraction. We compared the concentrations of hydrophobic DOM estimated by the UV method with those of the conventional fractionation using chromatographic columns of XAD-8 macroporous resin and found an excellent agreement between the two methods for both solutions from laboratory sorption experiments and field samples of forest floor leachates and subsoil porewaters. In addition, the absorption at 260 nm of hydrophobic DOM proved to be independent of pH values ranging from 2.0 to 6.5. Compared to the conventional chromatographic fractionation, the method using the UV absorption at 260 nm is less time consuming, needs a much smaller sample volume, and showed a better reproducibility. However, its use is restricted to water samples of low nitrate (< 25 mg L(-1)) and Fe (< 5 mg L(-1)) concentrations and, probably, with the hydrophobic fraction dominated by aromatic compounds deriving from degradation of lignin.

Carbon↗
PubMedDate not supplied

Induced contrast asynchronies may be useful for luminance photometry.

Shapiro et al. (2004) introduced a new visual effect (the induced contrast asynchrony) that demonstrates a perceptual separation between the response to a modulated light and the response to contrast of the light relative to background. The effect is composed of two physically identical disks, one surrounded by a dark annulus and the other by a light annulus. The luminance levels of both central disks were modulated in time, producing a stimulus with in-phase luminance modulation and antiphase contrast modulation. Observers primarily perceived the disks to be modulating asynchronously (i.e. they perceived the contrast), but at low temporal frequencies could also track the luminance level. Here we document that the induced contrast asynchrony disappears when the surrounds are achromatic and the center lights are modulated near the equiluminant axis. Observers viewed 1-deg-diameter disks embedded 2-deg-diameter achromatic surrounds. The chromaticity of the disks was modulated in time (1 Hz) along lines in an S versus Luminance cardinal color plane and an L-M versus Luminance cardinal color plane; observers responded as to whether the modulation appeared in phase. For all observers and both color planes, the lights appeared in phase most frequently at angles near the standard observer's equiluminant line and out of phase at angles further away from that line. Observers differed in the range of angles that produce the appearance of in-phase modulation. The results suggest that induced contrast asynchronies may be useful as a technique for equating luminance of disparate lights.

Adult↗
PubMed1998

An infra-red light-transmitting aperture controller for use in single-cell fluorescence photometry.

Photometric techniques are commonly used to monitor the output from fluorescent indicators during the study of cellular signalling. At the single-cell level, the region of interest is normally set by a variable aperture placed within the microscope emission pathway. The present study reports an improved aperture controller which adjusts the area for fluorescence measurement, whilst allowing objects throughout the field of view to be continuously monitored using infra-red illumination. A rectangular aperture is selected by four 715-nm long-pass glass filters which block > 99.9% of the fluorescence emission at 480-600 nm. A 780-nm long-pass glass filter is used to provide infra-red illumination which does not interfere with the fluorescence signal, yet is detectable by a standard CCD camera. This allows detection of morphological events throughout the field of view and facilitates manipulation of extracellular pipettes, without interruption to a single-cell fluorescence recording. The infra-red light-transmitting controller is suitable for use with a range of other fluorescent indicators, including those routinely used to detect Ca2+, Cl-, Na+ and pH. Data are presented which demonstrate the use of this controller to measure ADP-evoked [Ca2+]i increases in single human erythroleukaemia cells loaded with the Ca2+ indicator fura-2.

Adenosine Diphosphate↗
PubMed1986

Reflection photometry of oxygen supply of skin flaps and replanted fingers.

A method is presented that allows noninvasive, direct, and rapid control of the oxygen supply of the skin, by registration of cutaneous hemoglobin spectra. Axial pattern flaps, free transfer flaps, and replanted fingers were investigated using this method intra- and postoperatively. The results showed that with such a control, complications in the revascularization and healing process can be detected fairly early, so that therapeutic measures can be taken.

Fingers↗
PubMed1956

Flame photometry.

Explore the source record for details and available documents.

Photometry↗
PubMed2004

Photometry in the workplace: the rationale for a new method.

OBJECTIVES: The assessment of lighting conditions in workplaces has traditionally focused on the measurement of illuminance. The rationale for a new method for the detailed evaluation of natural and artificial light in 'near work' situations, involving the assessment of luminance, is described. METHODS: The procedure comprises four successive phases: (1) identify object/images observed during work tasks; (2) outline the area of the operator's visual field where gaze is predominantly directed; (3) measure luminances in the visual field, pin-pointing all sources of primary and secondary luminance, and constructing iso-luminance maps; and (4) compare luminance ratios. RESULTS: The procedure was illustrated using the common example of near work in an office environment. Illuminance was found to be inadequate to evaluate the effects of natural and artificial environmental light in the workplace. This is due to the fact that the luxmeter is designed to integrate the light detected over a large angle, whereas in near work the operator's retina is mainly stimulated by light originating from objects/images placed in the occupational visual field. CONCLUSIONS: A detailed measurement of luminance within the occupational visual field is consistent with ocular anatomy and physiology, and can be used as part of a risk assessment for visual disturbances and to rationalize lighting at workstations.

Asthenopia↗