11
3.2
Spectroscopy Measurement
There are four main components of a spectrophotometer. These are a light source to emit a high and constant
amount of energy over the full wavelength range; a method for separating the light into discreet wavelengths; a
sample holder and a light detector.
The optical layout of the 7410 and 7415 spectrophotometers is shown below:
The light from the pre-focused tungsten halogen (7410) or pre-aligned xenon (7415) lamp is focused onto
the grating, with 1200 lines per millimetre, which separates the light into discrete wavelengths. The diffracted
spectrum of light then passes through a further slit and lens arrangement before passing through the sample in
the sample chamber from left to right. The light which is not absorbed by the sample is transmitted through a
collecting lens and onto the signal detector. The photo-diode detector used is mounted directly onto the detector
PCB and the output is used to calculate the % transmittance. The result is displayed either as % transmittance or
absorbance on the instrument display.
Exit Slit
Entrance Slit
Lamp
Grating
Collimator Mirror
Detector
Collecting Lens
Sample
