Light microscopy
Light microscopy is a central instrument in materialography and the oldest and most essential microscopy technique. It uses visible light and optical lenses to produce a magnified image of the object analysed.
Table of contents
What is a light microscope?
A light microscope, also called an optical microscope, is an instrument that uses light and lenses to depict small structures and objects with magnification. It typically consists of a light source, condenser lenses for focusing the light, objective lenses for the initial magnification and ocular lenses through which the observer can see the magnified image.
What can be analysed using a light microscope?
Light microscopes are often used in scientific and industrial areas. In the scientific area, they are used to analyse biological samples, cells, tissue, minerals and other materials.
In the industrial area and especially in material analysis, light microscopy provides assistance during the analysis of surface structures, particles in powders, defects in materials, as well as the general arrangement of material components and during microstructure analyses.
Light microscopy
at Quality Analysis
Detailed analysis of materials and component characteristics
The latest light microscopy is used in our test laboratory to make the finest structures, defects or contamination visible. In this way, we can analyse material samples at the microscopic level and precisely evaluate the quality as well as the integrity of the materials analysed. We undertake not only a thorough defect analysis, we also provide comprehensive quality assurance and innovative solutions to our customers in various sectors.
- Analysis of different materials and surface structures, as well as powders and material defects
- Analysis of the microstructure of metals to obtain information about grain size, phases and possible contamination
- Analysis of polymer structures and identification of defects such as cracks or inclusions
- Large range of light and electron microscopes for the identification of the smallest damaged areas
- Particle analysis and microstructure analysis using light, laser scanning and electron microscopy as well as RAMAN and FTIR spectroscopy
The design of a classic light microscope
A light microscope consists of several important components that work together to magnify small structures and produce detailed images. At the top of the microscope is the ocular lens, that is the lens through which the observer sees the magnified image. The tube that connects the ocular lens to the objective lenses determines the magnification of the image; a longer tube permits greater magnification. The objective lenses at the bottom end of the tube are the primary magnifying lenses. Several objective lenses are fastened to a nosepiece, which makes it possible to change quickly between different magnifications.
The analysis of an object using a light microscope
The object analysed is placed on a slide, a small glass plate, and fixed to the microscope's stage to prevent movement during the observation. Underneath the stage is the condenser that bundles the light and focuses it on the sample to improve the illumination and therefore the image quality. The light source, which is often on the base of the microscope, illuminates the sample from below. It ensures sufficient, even illumination, which is crucial for the clarity and level of detail of the image.
Different types of light microscopy
In light microscopy, a differentiation is made depending on the type of illumination. In transmitted light microscopy the light is guided from below through a transparent sample and in this way inner structures made visible. In reflected light microscopy, on the other hand, the light illuminates an opaque sample from above and the reflected light is observed. Brightfield microscopy uses an even, bright light field; the sample appears dark against a bright background. In darkfield microscopy the sample is illuminated by light incident from the side, such that the sample appears bright against a dark background. All types of light microscopy produce significantly magnified images making visible fine details, which would not be apparent to the naked eye.
Transmitted and reflected light microscopes
In light microscopy, there are various methods of illumination that are selected depending on the type of sample and the details required.
In transmitted light microscopes, the light is guided through the sample from below. This method is particularly suitable for thin, transparent samples, such as biological cross-sections. The light passes through the sample and produces contrast based on the different densities and structures inside the sample.
Conversely, in reflected light microscopes the light is directed onto the sample from above. This technique is often used for opaque or reflective samples, e.g. metal surfaces or thicker pieces of tissue. The reflected light is then collected by the objective lens and permits the assessment of the surface of the sample.
Brightfield and darkfield microscopy
A further important difference in light microscopy relates to the illumination techniques used to produce the image.
Brightfield microscopy is the commonest form of light microscopy. For this purpose, the light is guided directly through the sample and makes possible a clear, high-contrast image. Bright areas on the image correspond to areas where the light passes unhindered through the sample, while darker areas indicate structures and density differences.
Darkfield microscopy, on the other hand, uses a special illumination technique in which the sample is exposed to light from the side. In this way, only the light scattered by structures in the sample is guided to the objective lens. The result is a bright image of the structures against a dark background. This technique is particularly useful for enhancing fine details and contrast that may not be visible in brightfield microscopy.
Advantages and disadvantages of light microscopy
Light microscopes are widespread due to their versatility and ease of use. This is partly due to the fact that they offer a cost-effective option for magnifying samples and observing them in detail. Light microscopes permit the observation of living samples, without having a negative effect on them. Several structures can also be depicted at the same time by using different colours of light. As such, light microscopes are ideal for numerous applications in biology, medicine and materials science.
The disadvantage of light microscopy is its resolution. A significantly higher resolution can be obtained using an electron microscope: while a resolution of only approx. 1 µm can be achieved using a light microscope, up to 1 nm magnification can be achieved using an electron microscope.
Also ideal for microscopic structures:
Electron microscopy
Along with light microscopes, electron microscopes are used for the analysis of very small structures, because they offer a higher resolution.
Electron microscopes are high-resolution microscopes that use electron beams instead of light to observe objects with an extraordinary level of detail and magnification. They are particularly useful for the analysis of nanoscopic and microscopic structures at the atomic and molecular level. An important type is the scanning electron microscope (SEM), which produces detailed 3D images of the surface structure of samples by scanning the sample using electron beams. As such, SEM provides a high depth of field and high resolution, which permit the detection of the finest surface features and topographical details.
How does light microscopy differ from electron microscopy?
Light microscopy and electron microscopy differ fundamentally in their principle of operation and their applications. Because visible light and optical lenses are used in light microscopy to magnify samples, it is ideal for the analysis of the microstructure of materials, including the grain structure in metals, the phase distribution in alloys and the identification of material defects such as cracks or inclusions.
On the other hand, electron microscopy is significantly more elaborate and complex. This situation is due to the need for special sample preparation and protective conditions such as the necessary vacuum. However, as a result, it offers an extremely high level of detail, as is important particularly during the analysis of materials, nanostructures and biological samples at the molecular level.
Modern light microscopic methods
The development of light microscopy has advanced significantly in recent decades and it has become an indispensable tool in materials sciences. Modern techniques such as laser scanning microscopy have made it possible to scan samples with a finely focused laser beam and produce high-resolution, three-dimensional images. In this way, it is possible to make visible detailed structures and surface features of materials that it would not be possible to detect using conventional light microscopes.
The different types of light microscopy
A further advance is fluorescence microscopy, which is used in materials sciences to mark and make visible specific molecules or particles within a material. Also, techniques such as phase contrast microscopy and differential interference contrast microscopy (DIC) have expanded the possibilities for analysing transparent, low-contrast samples in detail.
The systematic further development of techniques and their combination with other analytical methods now make it possible to identify microscopic details and defects as well as analyse their cause, something it would not have been possible to depict in the past. Among other areas, this situation is vital for the development and improvement of materials.
Applications for light microscopy
Light microscopy is an indispensable tool for the analysis of the microstructure of materials, including the grain structure in metals, phase distribution in alloys and the identification of material defects such as cracks or inclusions. These detailed analyses are crucial for material characterisation, quality control and product development in various industrial sectors such as the automotive sector, medical technology or additive manufacturing.
Additive manufacturing
During the manufacture of components using additive methods, incorrect process parameters or poor powder quality can cause layers in the material to become detached. Light microscopy depicts these delaminations with high resolution and permits precise measurement. By analysing the microstructure, defects in the manufacturing process can be detected and prevented.
Automotive
In the automotive industry, light microscopy is used to analyse particulate contamination, among other aspects. In particular, in electronic components it permits, in combination with scanning electron microscopy, RAMAN and FTIR spectroscopy, the exact determination of the size, material and damage behaviour of the particles. The precise analytical results contribute to the improvement of the quality and reliability of automotive components.
Medical technology
In medical technology, light microscopy plays a crucial role during quality control and research. It permits detailed analysis of medical implants, microsurgical instruments and biocompatible materials. By analysing the microstructure and surface characteristics, it is possible to detect manufacturing defects and ensure bio-compatibility.
Light microscopy in summary
Light microscopy is a central tool in materials sciences. It uses visible light and lenses to analyse the microstructure of materials. In this way, it permits the analysis of grain structures, phase distributions and material defects such as cracks or inclusions. Modern techniques such as laser scanning microscopy provide high-resolution, three-dimensional images, which are indispensable for quality control and the further development of materials.
