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Illumination | Illumination

Key Words: photobleaching, phototoxicity, lasers, confocal, FRAP, FLIP, diascopic, episcopic, CLEM, oblique illumination, Excitation, Koehler, mercury fiber illuminator

Definition:Microscope Illumination is the radiation incident to a specimen


Microscope Illumination is perhaps the most critical factor in determining the overall performance of the optical system and should be bright, glare-free and evenly dispersed in the field of view. Various illumination systems are available depending on the imaging technique and the application and may be integral to the microscope or external to it. The use of diascopic or episcopic illumination, wavelength range, intensity and angle of illumination all affect imaging and the information that can be gained from the specimen. Illumination may also be modified for specialized techniques with the addition of filters, polarizers, phase rings etc.

Most microscopes incorporate an integral tungsten-halogen bulb that can be easily controlled in intensity. Mercury vapor, xenon and zirconium arc lamps are also useful sources of illumination for specialized forms of microscopy. In fluorescence imaging, for example, the light source must be powerful enough to produce observable fluorescence from fluorophores in the specimen. Mercury and xenon arc-discharge lamps are most commonly used in widefield fluorescence applications, while lasers are necessary for laser scanning confocal applications. Lasers have the advantage of small source size, while providing high intensity light, which can be modulated using AOM or AOTF technology.

In biological environments the ability to precisely target and modulate the intensity of illumination (especially in confocal fluorescence imaging) is desirable for preserving cell viability. The ability to target laser illumination precisely is essential to techniques such as FRAP and FLIP.


Correct illumination is required for all microscopy imaging applications in both biological and industrial fields. For optimal imaging all optical components in the microscope, including the illuminator, must be set up and aligned correctly. Stable, no-flicker, light intensity is, in addition, a requirement for epi-fluorescence imaging.


Nikon supplies a wide range of illumination systems designed for specific imaging techniques in both biological and industrial environments. Nikon also supplies a number of technologies designed to target and modulate illumination intensity, such as Intensilight (mercury-fiber illuminator for epi-fluorescence) and the CLEM system for confocal fluorescence live cell imaging.


The illumination system will depend on the imaging technique and the application. Please consult you local Nikon representative for advice.


Illumination for stereo microscopy (reflected) [microscopyu] 

Illumination for stereo microscopy (oblique) [microscopyu] 

Illumination for stereo microscopy (darkfield) [microscopyu]

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