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The light source used in a transmitted- or reflected-light microscope. For most routine work, an incandescent, tungsten filament lamp with a variable rheostat is used. The colour temperature is normally about 2800 K and a pale blue filter may be used to provide a more daylight-like colour temperature. The standard illuminating system may contain additional lenses, diaphragms, and a polarizer.

Subjects: Earth Sciences and Geography.

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