Light Microscope: Definition, Uses & Parts

Lesson Transcript
Instructor: Cassandra Marnocha
Observation is an essential part of science, especially biology. Objects like bacteria, however, are too small to observe with the naked eye. For this reason, the light microscope has become an important and widely used tool for scientists. Updated: 01/31/2020

Definition of Light Microscopy

A light microscope uses focused light and lenses to magnify a specimen, usually a cell. In this way, a light microscope is much like a telescope, except that instead of the object being very large and very far away, it is very small and very close to the lens.

Light microscopes send light through a path that first focuses the light into a tight beam and then passes that light through a sample, which creates an image. That image then passes through one or more lenses to magnify it until it reaches the user's eye or a camera. Because light needs to pass through the sample, it must be either very small or very thin. Most cells (bacterial or otherwise) are both small and transparent, and so light can easily pass through them.

Light microscopes can come in several forms. Simple light microscopes use a single lens to magnify an object and cannot reach high magnification. Compound light microscopes use two sets of lenses - an objective lens and an eyepiece - to produce images. Monocular microscopes have one eyepiece, while binocular microscopes have two eyepieces and reduce eye strain.

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  • 0:00 Definition of Light Microscopy
  • 1:09 Uses of Light Microscopy
  • 2:39 Parts of a Light Microscope
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Uses of Light Microscopy

Microscopes are essential tools for scientists. They are used in microbiology, material science, mineralogy and medicine.

A combination of staining and light microscopy can allow scientists to identify different kinds of bacteria. Staining involves adding special dyes to a smear of cells. These stains are diagnostic for different kinds of cell membranes. Gram staining, for instance, uses crystal violet to stain Gram-positive bacteria and safranin to stain Gram-negative bacteria. These will show up in the light microscope as purple Gram-positive cells and pink Gram-negative cells.

Mineralogists also use light microscopy, typically with a special preparation of a sample called thin sections. As the name implies, thin sections are very thin slices of a rock. The sample needs to be thin enough for light to travel through from the light source to the user's eye. The thin section will allow the shape of different crystal grains to be seen. These shapes can tell the user what kinds of minerals are found in the sample.

Light microscopes are very much an 'easy to learn, hard to master' type of equipment. The microscope can be used with different techniques, like epifluorescence and phase contrast. Just about anyone can learn to use a microscope, but mastering techniques to produce the best quality image at high resolution can take years of training and practice.

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