METHOD 6242.2
March 22, 2001
INFRARED REFLECTANCE FROM REFLECTOMETER
1. SCOPE
1.1 Scope. The reflectometer test method is designed to provide a simple photoelectric means for
evaluating the infrared reflectance of a specimen by comparison with a spectrophotometrically
calibrated standard. This method is supplementary to the spectrophotometric method 6241.2. When
results obtained by those two methods disagree, the results from the spectrophotometric method
will govern.
2. APPARATUS
2.1 Apparatus. Use an apparatus that provides a means for irradiating the test specimen and of
indicating the radiation reflected by the test specimen. Use an appropriate spectral irradiation from
the source and the spectral sensitivity of the receiver to cover the spectral band in which the
measurements are made.
2.1.1 Geometry. Use the following geometry of irradiating and viewing that is measured from
the perpendicular to the irradiated face of the test specimen:
Irradiating
Viewing
0°
Hemispherical
0°
Hemispherical
The area irradiated should be sufficiently large to be representative of the test specimen. Other
geometries of irradiating and viewing may be employed provided the results obtained are
comparable to the results obtained by specified geometries. Any reflectometer that yields results
comparable to those obtained from the spectrophotometric method may be used.
2.1.2 Reflectometer for the spectral region covered by the 30 wavelengths listed in table I,
method 6241.2. Although it does not have the preferred geometry, a Hunter Multipurpose
Reflectometer using a Wratten 88 or 89B filter and photovoltaic-type photocell with standards
described in 2.2 may be used. Another photometer employing an S-l phototube has been found to be
satisfactory when employed with a suitable source and filter combination. Use a source consisting
of a tungsten lamp operating at a color temperature between 2,800° and 2,950° Kelvin. An
interference-type filter having a peak transmission at 0.79 micrometer in combination with a
Wratten 89B filter is placed in front of the phototube, which provides hemispherical irradiation and
perpendicular viewing.
2.1.3 Reflectometer for the spectral region covered by the 10 wavelengths listed in table II of
method 6241.2. The photometer described in 2.1.2, employing the S-l phototube and tungsten light
source together with a suitable filter is satisfactory. A glass filter having the following transmission
characteristics has been found to be adequate: 3 ± 1 percent at 0.9 micrometer, 29 ± 3 percent at 1.0
micrometer. A Corning glass filter No. 2540 can be obtained to meet these requirements.
FED. TEST METHOD STD. 141D
1
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