4: Sample Experiments
Click the Store Reference spectrum icon on the toolbar or select Spectrum | Store Reference
from the menu bar to store the reference. This command merely stores a reference spectrum in
memory. You must select File | Save | Reference from the menu bar to permanently save the
spectrum to disk.
4. Block the light path to the spectrometer. Then, take a dark spectrum by clicking the Store Dark
Spectrum icon on the toolbar or by selecting Spectrum | Store Dark from the menu bar. This
command merely stores a dark spectrum in memory. You must select File | Save | Dark from the
menu to permanently save the spectrum to disk.
Note
If possible, do not turn off the light source when taking a dark spectrum. If you must turn
off your light source to store a dark spectrum, allow enough time for the lamp to warm up
again before continuing your experiment.
You must take a dark spectrum before measuring transmission.
5. Put the sample in place and verify that the light path is clear. Then, take a transmission
measurement by clicking the Transmission Mode icon on the toolbar or selecting Spectrum |
Transmission Mode from the menu bar. To save the spectrum to disk, click the Save icon on the
toolbar or select File | Save | Processed from the menu bar.
Note
If you change any sampling variable (integration time, averaging, smoothing, angle,
temperature, fiber size, etc.), you must store a new dark and reference spectrum.
Reflection Experiments
Reflection is the return of radiation by a surface, without a change in wavelength. Reflection can be:
• Specular (the angle of incidence is equal to the angle of reflection)
• Diffuse (the angle of incidence is not equal to the angle of reflection)
Every surface returns both specular and diffuse reflections. Some surfaces may return mostly specular
reflection, while others may return mostly diffuse reflection. Specular reflection increases proportionately
with the amount of gloss on a surface.
Reflection is expressed as a percentage (%R
λ
) relative to the reflection from a standard reference
substance:
S
λ
- D
λ
%R
λ
R
λ
- D
λ
x 100%
22 220-00000-000-02-0605
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