Powerful compact light sources, such as high-energy short arc-discharge lamps, are necessary in order to produce enough excitation light intensity to produce visible emission in fluorescent microscopes. Mercury burners (50 to 200 Watts) and the Xenon burners (75 to 150 Watts) are the usual lamps for fluorescent microscopes. These light sources are usually powered externally by a direct current supply which furnishes enough start-up power to incite the burner through ionization of the gaseous vapor and to keep it burning with minimum flicker.

The fluorescent microscope arc-discharge lamp external power supply is usually comes with a timer to record the number of hours the burner has been used. If used beyond their rated lifetime of approximately 200-300 hours, the arc lamps’ efficiency drops and is likely to break. When considering the efficiency of the illumination, lamp wattage is not the only factor to consider. The most important parameter to consider is the mean luminance, keeping in mind the source brightness, arc geometry, and the angular spread of emission. The mercury burners do not provide constant intensity across the spectrum from ultraviolet to infrared. Instead, the intensity of the mercury lamp is spent in the near ultraviolet with intensity peaks prominent at 313, 334, 365, 406, 435, 546, and 578 nanometers. The intensity is stable although not nearly so bright at other wavelengths in the visible light region but it is still employable in most applications.

Upcoming light sources for fluorescent microscopes include laser light sources. An increase in the application of laser light sources, particularly the argon-ion and argon-krypton (ion) lasers have been experienced by optical microscopy in the past few years. Small source size, low divergence, near-monochromicity, and high mean luminance are only some of the advantages of these lasers. They have become vital in scanning confocal microscopy, a fluorescence technique that is a powerful tool in rendering very clear and sharp fluorescence images through elimination of non-focused light isolated from the specimen focal plane. This task is accomplished by confocal microscopes through line or point scanning with concurrent imaging through a conjugate aperture. The specimens’ optical sections can be saved in a computer and restructured into the final image. The final product is then shown on the monitor.

Studies have been made on the various combinations of light sources and filters to produce optimum images. A quantitative study of the efficiency of various combinations of primary and secondary filters, and light sources for the fluorescent microscope with chromosomes stained with quinacrine mustard or quinacrine has been done. In this study, strong fluorescence using epi-illumination could be achieved with a mercury or xenon lamp in combination with two KP 490 short-wave pass interference filters (tilted to an angle of 60° with the excitation beam) as primary filter, and a K 490 as a secondary filter. The mixture of a mercury lamp and a narrow band interference filter with a maximal transmission at about 436 nm as a primary filter together with a K 490 secondary filter results in a fine visual image contrast, satisfactorily strong fluorescence, and a relatively slow rate of fading (Springer Berlin / Heidelberg, 1972).