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Colibri – LED Technology for Fluorescence Microscopy
Sponsored,vendor-submitted protocol   Published in BioTechniques Protocol Guide 2008 (p.53)

With Colibri, Carl Zeiss MicroImaging GmbH is introducing an innovative light source that will bring the numerous advantages of LEDs (Light Emitting Diodes) into the fluorescence microscopy domain.

LED technology has developed rapidly over recent years in terms not only of available wavelengths but also of emission performance, so that LEDs have come to be used in a wide range of applications. Their compact design, low power consumption, minimal heat output, fast switching and adjusting properties, high emission stability and extremely long life span are all features that make the use of LEDs very attractive—not least for fluorescence microscopy. It is precisely these characteristics that conventional arc lamps, such as HBO, XBO or metal halide lack to varying degrees.

It used to be virtually impossible to use LEDs in fluorescence microscopy because of their low emissions. However, the high-performance LEDs available today have overcome this hurdle. And their performance is continuing to increase, by some 20% per year on average.

Colibri's extremely modular design ensures that it will be easy to implement and exploit further developments in LED technology in the future as well.

Ten different LED modules are already available for Colibri, from UV to dark red.

Every individual LED module emits only a precisely defined spectral range. What at first glance might seem to be a disadvantage compared to arc lamps, which emit light across the entire spectral range, proves on closer inspection to be beneficial: it is only the wavelength range that coincides with the absorption spectrum of a fluorescent dye that contributes to the excitation of that dye. All other wavelengths have to be suppressed as fully as possible; otherwise they will superimpose the fluorescence signal.

Modern fluorescence filters achieve excellent suppression of unneeded wavelengths, but they do not suppress them completely. And every undesirable photon that finds its way to the detector adds to the image background, causing deterioration in the signal-to-noise ratio.

LEDs, on the other hand, always emit only one particular wavelength range. Outside this range, they shed no light whatsoever that could increase the image background. The result is extremely high-contrast fluorescence images with a high dynamic range that enable the detection of the weakest of signals and the finest of structures.

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