Microscopes are ubiquitous devices for peering into the world of very small objects, details or organisms. These delicate pieces of equipment are essential to several kinds of analytical settings – from clinical laboratories to forensic investigation units. In this regard, light and electron microscopes are among the most common variants one can encounter in any laboratory.
How is a light microscope different from an electron microscope?
The main difference between light and electron microscopes concerns their mechanism for magnifying objects under the lens: light microscopes use visible light refracted and focused by their glass lens to zoom in on an object, while electron microscopes fire an electron beam to provide a very high-resolution image of their specimen.
What is a Light Microscope?
Light (or optical) microscopes magnify a subject using visible light. The way the specimen absorbs, scatters or reflects this light provides a more detailed view of its features – in essence, its image is magnified when viewed by the right type of lens.
A modern light microscope itself works when an illumination source (typically a bulb or LED lamp at the base) casts light that passes through a specimen and into the imaging system, comprised by the lens that magnifies the object.
Simple variants use only a single lens, while compound light microscopes provide a higher total magnification by using an eyepiece lens aligned with an objective lens.
Specimens have to be tiny and preferably transparent for the light to pass through the lens. Common subjects include blood or tissue smears, bacterial cells and other microbes.
What is an Electron Microscope?
Instead of visible radiation, electron microscopes use concentrated beams of electrons to illuminate their specimens. An electron beam’s wavelength is shorter than that of visible light, leading to a much higher resolution – usually a 1000-fold increase in detail.
An electron microscope can fall under one of two main categories:
- Scanning EM (electron microscope). A SEM allows for a very high-resolution look at the surfaces of tissues, microbes or other cells. The very narrow electron beam doesn’t pass through the specimen, but creates a three-dimensional view of the subject.
- Transmission EM. A TEM has electromagnetic lenses that focus its electron beam onto a specimen, producing extremely high-resolution (upwards of 100,000x times) images with whiter (electron-lucent) or blacker (electron-dense) areas.
Differences between a Light Microscope and an Electron Microscope
Source of Illumination
Mechanically, this is the most significant point of difference between light and electron microscopes.
Optical microscopy uses light in the visible spectrum. The source is oftentimes a lamp attached to the base; the most popular lamp type uses an incandescent tungsten-halogen bulb, while LED bulbs are more common among fluorescence microscopes.
Meanwhile, electron microscopy makes use of a concentrated electron beam fired from an electron gun. The process takes advantage of how electrons can behave similarly to photons (light particles) when inside a vacuum.
Imaging System
In a light microscope, visible light strikes a specimen, producing an image, before passing through the convex lens by which the image can be viewed.
Due to the increased magnification provided by its eyepiece and objective lens, compound microscopes give a clearer and closer look at a subject compared to a one-lens simple microscope.
Furthermore, light microscopy lenses have a fixed focus, and the distance between an objective lens and the specimen is variable.
Electron microscopes, however, use variable-focus electromagnetic lenses which have a fixed distance from the specimen. Rather than being a solid material like glass through which the electron beam passes, this type of lens creates a focused magnetic field to bend the beam.
Color
Many types of light microscopes exist – brightfield, fluorescence, polarizing, and phase-contrast variants are available. While the images produced by each unit differ in appearance, they are all invariably real images; users are seeing the actual color from these images.
Visible light – which provides color to images – has a far larger wavelength compared to the electron beams used by EM. As a result, EM images are black-and-white, and use false color to better highlight important details in a specimen.
There are efforts to provide real color imaging to electron microscopy.
Magnification
Electron microscopes have superior magnification ability; units can magnify tiny objects from 1 to 50 million times.
With a 100x oil immersion objective lens and a 10x ocular lens, light microscopes often have a total magnification of 1000x, although more powerful devices exist.
Resolution
In the context of microscopes, resolution refers to the device’s ability to display cells, particles or other objects as distinct things, rather than as a single blurred unit. Resolution is measured by the shortest distance between two objects so that they can be distinguished from each other.
Light microscopes have a resolution of roughly 200 nanometers.
Naturally, electron microscopes offer a much higher resolution compared to light microscopes. The resolution of most SEM devices can be approximately 100 times greater than that of an optical variant, translating to 0.2 nm.
Specimen
EM specimens must be extremely thin (below 0.1 micrometers). Only specimens that are dead or have been dehydrated are used. Scientists coat a specimen with very fine particles of conductive metal to make them easier to view and analyze.
Light microscope specimens can be much thicker, but ideally are 0.5 micrometers thick. To aid in identifying important details, scientists commonly wash their specimens with dyes, stains and other reagents.
Size
Light microscopes are much smaller than EM units. They also have the advantage of being highly portable.
The average optical microscope is small enough to be carried with both hands. The safe way to hold one is with one hand on its “arm” and another supporting its base from beneath.
In contrast, electron microscopes are large enough to require specialized rooms to keep them secure and free from magnetic interference. They can be roughly a meter tall or bigger.
Expense
Electron microscopes are obviously costlier to manufacture, use and maintain. Devices are large and bulky, contain many specialized parts, and require attentive care.
SEM units are less expensive compared to TEMs, although even a scanning EM can cost roughly 70,000 USD at the lower end, while advanced models can go for around 1,000,000 USD.
While light microscopes are still costly, they are far cheaper in relative terms; compound optical variants can be bought for around 900-1,200 USD.
Types
The majority of electron microscopes are either SEMs or TEMs. Reflection electron microscopes (REMs), which use elastically scattered electrons for its electron beam, also exist.
Compound light microscopy includes several variants, such as bright-field and dark-field, phase-contrast, polarizing, stereoscopic, and confocal.
Common Uses
Both microscopes are widely used in the field of microbial biology.
Light microscopes, due to their large variety, find a place in biotechnology, pharmaceutical, botanical, microelectronical or mineralogical laboratories.
Electron microscopes are involved in the same fields, but they are particularly useful in forensic science, virology, geology, and microchip production.
Comparison Chart: Light Microscope vs Electron Microscope
| Areas | Light Microscope | Electron Microscope |
| Source of Illumination | Visible light lamps | Electron beam gun |
| Imaging System | Fixed-focus, variable-distance lens | Variable-focus, fixed-distance lens |
| Color | True | False or black-and-white |
| Magnification | 10-1,500 times | 1-5 million times |
| Resolution | 200 nanometers | 0.2 nm |
| Specimen | Thicker, can be dead or alive | Very thin; dead or dehydrated |
| Size | Can be carried by hand | Large and bulky |
| Expense | 900-1,200 USD | 70,000-1,000,000 USD |
| Types | Simple, compound (brightfield, phase-contrast, polarizing, etc.) | Scanning (SEM), transmission (TEM), reflection (REM) |
How are Light and Electron Microscopes Similar?
Functionally, light and electron microscopes are similar because their primary purpose is to zoom in on a specimen, so that its details could be viewed at a significantly higher magnification and resolution.
Both microscopes also require electromagnetic radiation to function – visible radiation (light) for optical microscopes, and ionizing radiation (electron beam) for electron microscopes.
Furthermore, light and electron microscopes contain many delicate parts that make them highly sensitive to work with, and expensive to procure and maintain.
FAQ
What are the parts of a light microscope?
Students will commonly use a compound light microscope during laboratory activities. Such a device consists of a sturdy arm (carrying handle) attached to the flat base. Specific components include:
- Head
- Eyepiece or ocular lens (can be monocular or binocular)
- Nosepiece or revolving turret
- Objective lenses
- Mechanical stage, stage clips and aperture
- Coarse and fine adjustment knobs
- Stage controls
- Diaphragm, condenser, illuminator, brightness adjustment knob or dial, and light switch
Who invented the electron microscope?
German electrical engineers Ernst Ruska and his professor Max Knoll created the prototypical electron microscope in 1931 at the Berlin Technische Hochschule.
Later in 1937, Ladislaus Marton designed the first scanning-transmission electron microscope, while Cecil Hall, James Hillier and Albert Prebus would make the rough model for what would become America’s first commercially-available electron microscope.
With the groundwork they laid, electron microscopes by 1944 could provide resolutions as fine as 2 nanometers.
Conclusion
Microscopes are delicate but powerful marvels of modern engineering, and are indispensable as tools in the laboratory.
The key differences between light and electron microscopes is found in the source and nature of their illumination; the color, magnification, and resolution of the image they produce; and the specimens they require.
Light microscopes use light in the visible spectrum, which is projected by a halogen bulb, then condensed and focused onto a live or dead specimen on a glass slide; whereas electron microscopes utilize a concentrated electron beam fired from an electron gun onto a dead and dehydrated specimen.
Images from an electron microscope are false-color or black-and-white, but are highly superior in terms of magnification and resolution.
Additionally, SEMs or TEMs can tax a laboratory’s budget far more than a compound light microscope.
