Light intensity measurement

The S/N of any light intensity measurement varies as tire square root of tire intensity (number of photons) produced by tire source during tire time of tire measurement. The intensities typical of xenon arc lamps are sufficient for measurements of reasonable S/N on time scales longer tlian about a microsecond. However, a cw lamp will... 

Diverse instruments employing the principle of this experiment are used to measure mercury, a toxic and volatile element, present in many work areas. A device has been designed as a colorimeter dedicated for this single element. The source is a mercury vapour lamp and the cell is a transparent tube filled with the atmosphere to be monitored. If mercury vapours are present in the optical path, absorption of radiation emitted by the lamp will occur and this will lead to a decrease in the transmitted light intensity measured by the instrument. 

The accurate determination of incident light intensity is of pivotal importance in any quantitative photochemical experiment. While various physical devices are available for making absolute intensity measurements,168 these devices can be difficult to calibrate and usually are rather expensive. A much simpler approach involves the use of a chemical actinometer. This type of system is based upon a photochemical reaction for which product quantum yields are reasonably insensitive to variations in reactant concentration, temperature, light intensity and excitation wavelength. Once the quantum yield is calibrated by an absolute method, a chemical actinometer becomes a rapid, inexpensive and highly accurate secondary standard for light intensity measurements. 

The thermodynamic parameters were also calculated for Pluronic L-64 in water. Zhou and Chu (1994) took the CMT data obtained by scattered light intensity measurements from Pandya et al. 

Wilkinson s catalyst. Irradiation at 366 nm of 0.001 M RhCPPh NO and 1 M cyclohexene in o-dichlorobenzene was carried out under 1 atm H2 at room temperature. The hydrogen uptake was monitored using a mercury manometer attached to the reaction flask. Hydrogen was added periodically in order to maintain 1 atm pressure in the system. The solvent and olefin were distilled twice and degassed by three freeze-pump-thaw cycles before use. A 1000 watt Hg lamp filtered with a glass filter to isolate the 366 nm Hg line was used for all photolysis experiments. The light intensity, measured by ferrioxalate actinometry, was 1.0 x 10 6 einsteins/min. 

Of interest is the light intensity measured on plane II, located a distance / from plane I. Huygen s principle simply states that the field at plane II is the sum of spherical waves emanating from all points in plane I. However, the field at point A will be primarily influenced by the spherical wave at point A, with a similar relationship between the fields at points B and B. Fresnel s extension of Huygen s principle quantifies this statement. The spherical wave emanating from a differential area, dS, located at point A is... 

Fig. 19 Results of a diet study of surface-water ferrozine-reactive iron concentrations while following a body of water in the Gulf of Carpentaria, north of Australia. Plot A shows the light intensity measured over the day with the first point being at sunrise and the last at sunset. Plot B depicts filterable (< 0.4 pm) ferrozine-reactive iron concentrations for the same local time period. Plot C shows particulate ( ) and total ( ) ferrozine-reactive iron concentrations. Error bars indicate 98% confidence limits (from [153])...

Taylor DG, Demas JN. Light intensity measurements. I large area bolometers with microwatt sensitivities and absolute calibration of the rhodamine B quantum counter. II luminescent quantum counter comparator and evaluation of some luminescent quantum counters. Anal Ghem 1979 51 712-717, 717-722. 

Incident light intensity measured at the surface of photobioreactor. 

Fluorescence methods are inherently capable of detecting much lower concentrations of analytes, because of the instrumental principles involved. Consider, for example, a comparison of the light intensities measured in blank solutions by... 

Significant work has been conducted using light intensity measurements studying the birefringence of photopolymers (84), development of a controlled-rate thermomicroscopy system for both reflected and transmitted light (85), and the study of inorganic materials for a pyrotechnic system (86). 

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