The compound light microscope focuses visible light through a specimen. Different regions of the object scatter the light differently, producing an image. The use of light microscope is limited. A limit of a light microscope is that the user can view only two dimensional plane of the specimen at a time.
Electron microscope is a device for forming greatly magnified images of objects by means of electrons. Electron microscope serves primary two purposes:
i) the visual examination of structures too fine to be resolved with ordinary, or light microscopes, and ii) the study of surfaces that emit electrons. The first function made transmission electron microscopes essential research tools in biology.
Electron Microscope vs Light Microscope
Electron Microscope
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Light Microscope
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| Illuminating source is beam of electrons. | Illuminating source is light. |
| It is very large and complicated. | Microscope is compact and handy. |
| Only fixed specimens are studied. | Both living and fixed specimens can be studied. |
| The object is ultrathin, 0.1µm or below. | The object is 5 µm or thicker. |
| Only dehydrated specimens are used. | The specimen need not be dehydrated. |
| Vacuum is essential for its operation. | A vacuum is not required. |
| High voltage electric current is required(50,000 volts and above). | There is no need for high voltage electricity. |
| Tungsten filament is used to produce electrons. | A filament is not used. |
| It has a cooling system to take out heat generated by high voltage electric current. | There is no cooling system. |
| There is risk of radiation leakage. | Radiation risk is absent. |
| It employs elecromagnets. | Light microscope uses glass lenses. |
Image is formed due to scattering of electrons.  | Image is formed due to absorption of light waves.  |
| Image is seen only on a fluorescent screen. | Image can be seen directly. |
| Specimen is coated with heavy metals in order to reflect electrons. | Specimen is stained by coloured dyes. |
| Image is black and white. | Image is colored. |
| Resolving power is 0.5 -5.0 A0, through theoretically it can be 0.25 A0. | Resolving power is 0.25µm or 250nm (2500A0). |
| Magnification is up to 300,000. | Magnification is upto 4000. |
| Electron microscope is used in the study of external surface(Scanning Electron Microscope SEM) , ultra structure of cell and very small organisms(Transmission Electron Microscope TEM). | It is used for the study of detailed gross internal structure. |
