LightMicroscopy – The Light Microscope and The Electron Microscope

Light Microscopes are the most common microscopes, these are typical microscopes that you will have seen in school. These microscopes work like a magnifying-glass. They consist of an lenses and mirrors which lead the light coming from the small observed object directly into the observer's eye or any other light detecting device (such as a film or a digital camera). For that reason these microscopes are also called 'optical' microscopes.

The main advantage of light microscopes is that they are non-invasive (that is, they don't exchange matter with the observed object) and are not limited to surfaces of materials. The interior of any transparent body, like cells or crystals can be observed. The most serious limitation is the resolution limit. Resolution is the ability to distinguish between two points (for example if on a dark night, you are travelling in a car, and a car comes towards you with its headlights on, you can see only one light at first when it is far away, as it nears you are able to see the 2 headlights). The magnifying power is also less than for an electron microscope.

This is an image from an electron microscope…Can you guess what it is?

Electron microscopes use electron beams instead of light and magnets instead of lenses. One advantage of using electrons instead of photons (that is: light) is that the electrons have a wavelength that is thousands of times smaller. This means, that the resolution should be thousands of times better than in the optical microscope.So how do we use an electron microscope?

  • The prepared object is placed in the bottom of a special column that creates a vacuum when all the air is pumped out. At the top of the column is the “gun” that shoots out electrons. Inside the column are lenses that focus the electrons on the specimen.
  • Above the specimen, scanning coils move the electron beam back and forth across the entire object.
  • When the beam moves across the specimen, it knocks other electrons off. The movements of these electrons are recorded and enhanced. The microscope is able to create a picture of the specimen based on the way the electrons bounce off it. The picture appears on a monitor. What you see when you look through a light microscope is a magnified image made from light reflecting off an object. In the case of a Scanning Electron Microscope, you do not see light but the activity of the electrons.

Task 1. Read through the information above. You must concentrate on the differences between light microscopes and electron microscopes.

Task 2. Make a table to show the differences between light and electron microscopes (just like the one we did for prokaryotes and eukarotes). You may want to do a bit of internet research here – but don’t go crazy! Focus on magnifying power and resolution – possibly a few examples of what we can see with each type of microscope.