Bio-Rad SmartSpec Plus Spectrophotometer - Manual (Page 8)

5
UV/Visible Spectroscopy is based on the absorption of light as a function of wavelength.
All spectrophotometers have a light source that generates light of specific wavelengths. The
SmartSpec Plus uses a xenon flash lamp as its light source. Xenon flash lamps have several
advantages over the conventional light sources in that they reduce warm up time, do not heat
up the instrument and have a lamp life of 10 to 15 years. Additionally, xenon flash lamps emit
both UV and visible wavelengths, in contrast to deuterium lamps which emit only UV
wavelengths or tungsten lamps which primarily emit visible wavelenghts. In the SmartSpec
Plus, the xenon flash lamp pulses light only when measuring absorbance of a sample.
Fig. 5. A symbolic representation of the SmartSpec Plus optics module.
The path of light in the SmartSpec Plus is as follows:
Light from the xenon flash lamp
Lens
Sample
Lens
Slit
Concave mirror
Grating
Concave mirror
Photodiode array detector
The advantages of using a grating as a dispersion device are that:
1. They eliminate nonlinear dispersion.
2. Are not temperature sensitive.
Photodiode arrays have several advantages:
1. They acquire spectral data simultaneously without mechanically moving parts;
2. Have excellent wavelength reproducibility and,
3. A wide dynamic range.
It is also important to note here that in an array, several photodiode detectors are
arranged on a silicon crystal. The added benefit of an array is the ability to do side-by-side
readings, thus increasing speed.
Source
Lens
Sample Slit Grating Detector
Concave
Mirror Concave
Mirror