spectrophotometer

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun An instrument used to determine the relative intensity of various wavelengths in a spectrum of light.

from The Century Dictionary.

• noun An instrument used to compare the intensities of two spectra (as from the limb and center of the sun), or the intensity of a given color with that of the corresponding color in a standard spectrum.
• noun To serve as a spectrophotometer a spectroscope must he so constructed as to permit of the production side by side, wave-length corresponding with wave-length throughout, of the spectra of the two sources of light to be compared. It is also necessary to be able to vary the intensity of these spectra separately by any desired amount, and to measure the amount of such variation. In some instruments the light which is to form one of the spectra is introduced into the slit of the spectroscope by placing a right-angled reflection-prism over half the slit, as shown in Fig. 1. The sources of light to be spectro-photometrically compared being placed at A and B, the light from A enters the slit directly, while that from B is totally reflected within the prism into the other half of the slit. The line dividing the spectra, in instruments in which this device is used, lacks sharpness, and the ray from B suffers losses by reflection and absorption. To secure symmetry two reflecting-prisms are sometimes used, as in the horizontal slit photometer of Nichols (Fig. 2), in which the light from A and B is reflected into the slit from either side by means of the two similar prisms P, P. Numerous other devices have been employed for this purpose, one of the most satisfactory of which is that of the Lummer-Brodhun spectrophotometer. This instrument has two collimators, C and C′ (Fig. 3), mounted at right angles to each other. An arrangement consisting of two right-angled prisms placed together so as to form a cube (L), known as the Lummer-Brodhun body, transmits a portion of the light from C to the prism P and reflects a portion of the light from the collimator C′ at the surface separating the two prisms. The reflected beam, thus rendered parallel to that from collimator C, likewise enters the prism P, and both beams are dispersed, forming adjacent spectra which may be observed in the usual manner by means of the telescope T. In Brace's spectrophotometer (Fig. 4) the dispersing-prism P is split and a portion of the interface SS is silvered. A portion of the light from the collimator C passes through the unsilvered parts of the interface and enters the telescope T after dispersion in the usual manner. Light from C′ , reflected from the silvered strip, also enters T and forms a spectrum adjacent to that from C. In the spectrophotometric comparison of two sources of light, different regions of their spectra are isolated successively by means of a diaphragm in the eyepiece of the instrument. Each of these is brought in succession to the same intensity, and for each region the reduction to which the brighter of the two spectra must be subjected to produce equality is noted. It is then possible to express the brightness of one of the spectra, wave-length for wave-length, in terms of that of the other, which is called the comparison spectrum, and to express the relation between the two by means of a curve known as the curve of relative intensities. To produce equality of the spectra, Vierordt substituted for the slit of the ordinary spectroscope a double slit the upper and lower halves of which could be opened and closed independently by means of separate micrometer-screws. The brightness of the spectrum of the light entering either half of such a slit is approximately proportional to the slit-width, so that when the two spectra are equal the ratio of the intensities is readily computed from that of the slit-widths. In instruments of the Lummer-Brodhun type the measurement is made by adjusting the slits of the two collimators. Another means of equalizing the two spectra in a spectrophotometer consists in polarizing the light before dispersion and of regulating the light which reaches the eye by the rotation of a Nicol prism. The measurement of the angle between the plane of the polarizing prism and that of the analyzer gives the ratio of the two intensities. Such polarizing devices are used in the spectrophotometers of Hüfner, Glan, Koenig, Gouy, and others. To avoid the errors introduced by varying the width of the collimator-slits, the two spectra are sometimes brought to equality by placing in the path of the beam of light from the brighter source a revolving open-sectored disk so constructed that the openings are capable of adjustment during observation. The ratio between the open and closed sectors gives directly the reduction in intensity of the periodically interrupted beam. By means of the spectrophotometer it is possible to determine quantitatively the character of the light emitted by various fiames and artificial light sources, the selective absorption of substances through which light is transmitted, and the selective reflection of surfaces, and to find the distribution of energy in all sorts of continuous spectra.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Opt.) An instrument for measuring or comparing the intensities of the colors of the spectrum.
• noun (Chem., Physics) An analytical instrument for measuring the degree of absorption of light at different wavelengths by a chemical substance. A specific pattern of absorption intensities at a series of wavelengths is a characteristic of each different chemical substance.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun physics An instrument used to measure the intensity of electromagnetic radiation at different wavelengths.

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun a photometer for comparing two light radiations wavelength by wavelength