Light Sources
Light Emitting Diodes (LEDs) are miniaturized electroluminescent light sources that cover a range of 270 to 810nm. The width of their typical emission spectra ranges from 20 to 100nm and therefore it is necessary to select an LED suitable for a particular assay. This drawback can be overcome by packaging several LEDs into the same light source (A) or by using a Combination LED exhibiting a broader emission spectrum (B,C). Small size, low power consumption, robustness and long life time are reasons for selecting an LED. A super bright LED with the emission intensity of 270nm, and which can be tuned, is an excellent alternative to a deuterium lamp, both for absorbance and fluorescence spectroscopy. Note however, that it is always preferable to carry out spectrophotometry at two different wavelengths, the secondary serving as a reference, to stabilize the signal. With the excepting of Combination White LED (B,C) this option is not available for regular LED. A review of LED applications in FI (Frenzel and McKelvie 2008) summarizes LED properties, modifications and relevant literature.
Tungsten halogen light sources (360-2500nm) are available with 10000-hr lifetime bulbs, thus making them attractive as components of versatile systems, where selection of any section of visible and near-IR spectra is desirable http://www.oceanoptics.com/products/ls1.asp
Deuterium Tungsten Halogen light sources provide continuous spectrum in the range 215-2000nm. DTH sources are expensive , bulky and the deuterium lamp has a limited lifetime. Yet when a stable, high intensity light source covering UV-VIS-NIR range is needed, these DTH lamps are the only practical choice. http://www.oceanoptics.com/Products/dh2000.asp
W. Frenzel and I. D. McKelvie: Photometry Ch 12 in S. D. Kolev and I. D. McKelvie Advances in FIA and Related Techniques Elsevier Amsterdam 2008
1.4.14.
