Photometer, light source

Three special tristimulus light filters are available which, when combined with a specific light source and a filter photometer, can be used to obtain color data (20). Although this method provides added precision and accuracy, it is seldom worth the extra effort required (see Color). 

Photometer An analytical instrument containing a light source on one side and a light detector on the opposite side that measures the amount of light that passes through the sample. 

Temporarily close a shutter in front of the light source and measure the photometer response (dark-field measurement). 

Photometers are relatively simple devices that make use of a light source and one or more filters to present a narrow band of wavelengths to a sample and then to a photodetector. One, two, or even three wavelength analyses are possible with these devices. In addition, photometers are designed for location on-line, with samples generally plumbed into a sample cavity in the analyzer. 

Low Angle Laser Light Scattering Photometry. Weight-average molecular weights were determined with a KMX-6 photometer (LDC/Milton Roy). The light source was a 2 mW vertically polarized helium-neon laser (A =... 

Photometric emission measurements are carried out using either atomic absorption spectrophotometers without the light source, or flame photometers. The latter are... 

Colorimeter. An instrument for routine chemical analysis. Compounds or ions which absorb light in the visible part of the spectrum (400 to 800 nanometers) or which are convertible by specific reagents to such compounds can be analyzed with a colorimeter. The instrument typically incorporates an incandescent light bulb as light source, filters to separate the spectral region, a cuvette to contain the sample solution, and a photometer. See also Colorimetry,... 

The Model 835 multiwavelength filter photometer (Fig.3.44) provides energy at 254 nm with a low-pressure mercury lamp and at 280,313,334 and 365 nm with a medium-pressure mercury source. Selected wavelengths between 380 and 650 nm are also available with a quartz-iodine light source. Absorbance ranges of 0.01-2.56 AUFS are provided. Short-term noise levels are 5 X 10-s AU with the low-pressure mercury source and 1 X 10 4 AU with the other lamps. The design and dimensions of the cell are the same as for Model 840. A 24-jtzl cell is standard with the medium-pressure mercury lamp and the quartz—iodine lamp. 

Photometers are relatively simple devices that make use of a light source and one or more filters to present a narrow band of wavelengths to a sample and then to a photodetector. 

The standard Cone Calorimeter (Section 14.3.3.2.1) described in ASTM E 1354 includes a smoke photometer to measure light extinction in the exhaust duct. The system is based on a laser light source. The same system is also standardized internationally, although it is described in a separate document from the main Cone Calorimeter standard (ISO 5660-2). Smoke measurements are reported in terms of the average specific extinction area (ASTM E 1354 and ISO 5660-2) and the smoke production rate and total smoke production for the period prior to ignition and the flaming period (ISO 5660-2). 

The early workers in this field built their own apparatus, often assembling these from suitable units available from instruments for other purposes. Emission flame photometers have been converted into atomic absorption spectrophotometers by appropriate attachments consisting of specific light sources, choppers, and lenses, a principle also employed by some manufacturers. 

Two types of photometers are used in HPLC— the fixed-wavelength filter photometer and the variable-wavelength spectrophotometer. These use a low-pressure mercury arc lamp as a light source, a transmission or interference filter to isolate a narrow band of wavelengths of light with which to excite the sample, and a photodiode to detect the light transmitted through the sample. 

Operationally, the optical components used in turbidimeters and nephelometers are similar to those used in fluorometers or photometers. For example, the light sources commonly used are quartz halogen lamps, xenon lamps, and lasers. He-Ne lasers, which operate at 633 nm, have typically been used for light-scattering applications, such as nephelometric immunoassays and particle size and shape determinations. The laser beam is used specifically in some nephelometers because of its high intensity in addition, the coherent nature of laser light makes it ideally suited for nephelometric applications. 

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