Light Microscope vs Electron Microscope.

Both light microscopes and electron microscopes use radiation (light or electron beams) to form larger and more detailed images of objects (e.g. biological specimens, materials, crystal structures, etc.) than the human eye can produce unaided. (See also: What is eyesight ?)
An electron microscope is a microscope that uses beams of electrons instead of rays of visible light to form highly magnified images of tiny areas materials or biological specimens. Comparing light vs electron microscopes is made more complicated by the fact that there are different types of electron microscopes. The two main types of electron microscope are the Transmission Electron Microscope (TEM) and Scanning Electron Microscope (SEM). Other types of electron microscope include the Scanning Tunneling Microscope (STM) and Field Emission Transmission Microscope (FE-TEM).
Brief notes, see the tables lower down this page for figures, explanations and comments:

Similarities:	Form larger (magnified) and more detailed (highly resolved) images of small objects or small areas of larger objects e.g. a leaf, part of a bone, etc. than can be formed by the human eye. Used in study and research in biology and medical sciences (more about histology), material sciences e.g. metallurgy and other aspects of science. Specimens must be carefully prepared using techniques appropriate for both the equipment and the sample e.g. slicing, staining, mounting, etc. (e.g. how to prepare histology slides).
Differences:	Size: Light microscopes are smaller and lighter, so are easier to move and set-up. Cost / Availability: Light microscopes are less expensive than electron microscopes. Radiation Type: Light microscopes use light (approx wavelength 400-700 nm), electron microscopes use beams of electrons (approx equivalent wavelength 1 nm). Control of image formation : Light via glass lenses, beams of electrons can be focused using electromagnets due to negative charge on electrons. Resolution*: Electron microscopes have much higher resolution than light microscopes Magnification*: Electron microscopes have much higher magnification than light microscopes Colour Images: Light microscopes form images including the range of wavelengths (colours) provided by the light source - but remember that the colours seen are often due to stains rather than the actual colours present in nature). Electron microscopes produce greyscale (sometimes called "black and white") images. However, "false-colour" electron micrographs are common - and can be very beautiful! Preparation of specimens : Generally involves harsher processes, e.g. using corrosive chemicals, for viewing via electron microscope than preparation of slides for viewing using a light microscope. Therefore more skill required - both to prepare specimens and to interpret EM images (due to "artefacts" in images, artefacts = features in images that are not present in the specimen but rather are due to the processes used to prepare the specimen and produce the image) Image Formation : Light microscope images can be viewed directly. Electron microscopes require use of a fluorescent screen, photographic plate or electronic display because electrons cannot be observed directly by the human eye. Usage Limitations : Living specimens cannot be viewed using electron microscopes because electron microscopes require there to be a vacuum in the tube - otherwise the electrons would be absorbed by air molecules.
	* Differences due to the shorter equivalent wavelength of electron beams compared with visible light.

See the table at the bottom of this page for the advantages and disadvantages of light vs electron microscopes.
The following simple block diagram shows some of the basic similarities between light microscopes and electron microscopes (in general) by comparing the radiation pathways for a light microscope with a general electron microscope.

Very simple block diagrams of Electron vs Light Microscopes

Note: As light microscopes are commonly used in schools and colleges while electron microscopes are less widely available (due to cost and complexity) the more familiar light microscope is shown first (left) with an "equivalent" electron microscope represented on the right. In reality while the (light) source of a light microscope is usually near the lowest point of the instrument, the (electron) source of an electron microscope is usually towards the highest point of the instrument - see photos and YouTube clips, e.g. of how does a TEM work. Here, image detection is shown uppermost and the sources below in both cases for ease of comparison.

Compare Electron Microscopes vs Light Microscopes (Physical Aspects)

As there are different types of electron microscopes and capabilities vary the following comparison of electron microscopes with light microscopes is very general (including 'typical' rather than exact figures).

Light Microscope Electron Microscope Radiation Type Visible light Beams of Electrons Approx. wavelength of radiation 400–700 nm effective wavelength < 1 nm Radiation focussed by ... Lenses - usually glass lenses electromagnets Image formed by ... Light (of all colours whose wavelengths are supplied by the source of illumination) scatters from the various parts of the specimen and some of that scattered light reaches the objective lens (above the specimen) and is then re-directed through the objective and eyepiece lenses to form a focussed image. Re. TEM: Selective absorption of electrons by the specimen. (There must be a vacuum inside an operating electron microscope because otherwise the electrons would be absorbed by air molecules before they could reach the specimen.) Parts of the specimen absorb electrons and therefore appear dark on the micrograph, while other areas of the specimen allow electrons to pass through - causing those areas to appear bright on the micrograph. Image formed on ... The human eye can view a real image directly by looking into the eyepiece of the microscope. An image is then projected onto the retina of the eye. An image is formed by projecting a focussed image of the specimen onto a surface coated with electron-sensitive compounds. It may be labelled "fluorescent screen" on simple diagrams. Typical resolution Reported values vary from a typical 0.2-0.5 nm for TEMs, through 0.1 nm for STM, down to 50 pm (= 0.5 ångström = 0.05 nm) for FE-TEM. 1 pm = 1 picometre is 10-12m 1 Å (1 ångström) = 1 x 10-10m 200 nm 0.5 nm is the figure cited in AS Biology books 1 nanometre is 10-9m so 200 nm = 200 x 10-9m = 2 x 10-7m 1 nm (1 nanometre) = 1 x 10-9m, so 0.5 nm = 0.5 x 10-9m = 5 x 10-8m Compare the resolution of an electron microscope with that of a light microscope: resolution of electron microscope = 0.5 nm = 1 ... means that in very general terms, an electron microscope can detect and display around 400x as much detail as a light microscope, e.g. by imaging a line of 200 particles spaced with gaps whose size is equal to the particle size when the particle size is so small that the entire line is seen a single item when using a light microscope. resolution of light microscope 200 nm 400 Typical useful magnification Sources state between x1000 and x2000 Some sources state up to x10,000,000 less than x2000 usable image quality "at best" x1500 useful image quality typically up to x1000 approx x100,000 in SEM approx x250,000 in TEM Compare the magnification of an electron microscope with that of a light microscope: magnification of electron microscope = 100,000x ... means that in very general terms, an electron microscope can produce magnifications of at least 100 times greater than a typical light microscope magnification of light microscope 1000x Note: The figures used in the equations are indicated in red above. Notice the other values that could be used for this type of very general comparison.

Above: Table comparing the physics of light vs electron microscopes

Compare the Advantages and Disadvantages (i.e. limitations of use) of Electron Microscopes vs Light Microscopes

Due to constraints imposed by the ways in which different types of microscopes produce images, some microscopes can be used in certain ways that others cannot. For example, it is not possible to observe individual molecules using a light microscope or to watch living processes happen using an electron microscope.

Light Microscope (LM) Electron Microscope (EM) 1. Living cells & tissues Can watch living processes take place e.g. microscopic pond life in action, and even cell division. Not possible to view any living material due to vacuum inside EM 2. Thickness of specimen Specimen must be thin but can adjust focus to different positions (heights) within thin specimen on glass slide Very thin sections only in TEM Images surfaces (only) in SEM 3. Depth: 2D or 3D ? Image plane approx "flat" (2D) but, as above, can adjust focus through specimen 2D only in TEM ; SEM images surfaces - hence shows depth info that seems like 3D 4. Specimen preparation / artefacts Simpler preparation (staining still required) Harsher preparation procedures incl. use of corrosive chemicals that may cause "artefacts" in the resulting micrographs 5. Magnification Lower Magnification Higher Magnification - so several micrographs may be needed per specimen 6. Resolution Lower Resolution Higher Resolution - good for measuring sizes of smaller features

Above: Table comparing use of light vs electron microscopes