Light Source and Illumination System of the Microscope
The light source and illumination system provides light for illuminating specimens. Microscopes use two types of light sources: natural light and electric light sources. For microscopes adopting natural light, the light source system consists only of a mirror, also known as a reflector. It is mounted on the arm below the condenser. The mirror has two reflecting surfaces: one plane and one concave. It can be freely rotated both horizontally and vertically. Its main function is to redirect ambient light (the concave side also provides certain light condensing effect) to guide light toward the condenser lens.
Most modern microscopes are illuminated by electric light sources. Their light source system is composed of a light source lamp circuit, light source lamp, lens, mirror, condenser lens and other components. The entire illumination system is assembled inside the lamp housing. Tungsten lamps or tungsten halogen lamps are commonly used as light sources, with power ratings ranging from more than ten watts to tens of watts. The light source lamp generally operates at a low voltage below 12 V with adjustable voltage to vary light brightness. A light intensity regulator is usually integrated into the lamp circuit. Adjusting the regulator conveniently changes the brightness of light projected onto the specimen.
Circuit configurations for light source lamps vary widely. Voltage regulation is generally realized by adjusting the voltage on the primary winding of the transformer. Common methods include: changing the primary voltage of the transformer via switched series resistors on the primary side; adjusting the primary voltage by controlling the conduction angle of a thyristor using a unijunction transistor or diac.
