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Light microscopy

In its simplest form, light microscopy uses light to illuminate an object and a lens to magnify it. Depending on the type of microscopy and the purpose, different light sources can be used. These include natural light, light-emitting diodes (LEDs), metal halide sources, lasers, and tungsten,
halogen, mercury and xenon lamps.

The light microscope is a common tool that has been used to look at biological samples for many years and is still in wide use today. A light source below the sample creates a beam of light, which is focused before passing through the specimen and onto an objective lens. This magnifies the sample and the image is projected through an eyepiece, where it can be viewed or captured digitally.

This film features Spike Walker, a retired teacher who now has a well-equipped laboratory in his garage.


Polarised light microscopy

Based on traditional light microscopy, polarised light microscopy uses filters that allow only light travelling in a specific orientation to pass.

When this polarised light travels through certain materials, it is bent and split into two different components through a process called double refraction or birefringence. The resulting two rays of light are bent at different angles, which cause them to pass through the material at different speeds. The light rays then pass through a second filter perpendicular to the first, which again only allows light in a particular orientation to pass through. The combination of birefringence and the polarising filters causes the light to appear multicoloured, producing a colourful, abstract view of whatever is being sampled.


2017 Wellcome Image Awards winner: Cat skin and blood supply

Credit: David Linstead

Fluorescence microscopy

Fluorescence microscopy is widely used in biological research and is based on the principles of light microscopy. Fluorescence microscopy is often used to detect the presence of specific proteins in cells, using special markers called fluorophores. When the light from the microscope reaches these fluorophores they become excited and release light of a specific wavelength, appearing as a particular colour. Different proteins can be studied in the same sample through the use of different fluorophores. The most common fluorophores used emit red or green light.


2017 Wellcome Image Award winner: MicroRNA scaffold cancer therapy

Credit: João Conde, Nuria Oliva and Natalie Artzi