The Tungsten Standard
Most student microscopes today come prepared with a tungsten method of illumination. This is the standard form and a tungsten bulb is the cheapest and most common type of bulb used.
Tungsten microscope illumination has its pros and cons. First of all they are relatively inexpensive and asy to find and replace. They will also give a well defined and overall good viewing light. However, these products will produce a large amount of heat are not very long lasting and will have a low eye relief.
Halogen - does brighter and hotter mean better
Halogen bulbs for microscope illumination were introduced in the 1950s as a combination lamp so-named 'tungsten-halogen'. This lamp was very bright and allowed for confocal imaging. A pinhole was used to focus the light beam onto the target, thus making for sharper images.
In the 1980's, the halogen bulb was standard equipment for several brands of research microscopes. Later, in the new millennium, a form of microscope called a microprobe, was introduced using halogen lamps. This allowed for the elemental and isotopic analysis of solid objects.
Halogens are being used today in a variety of microscopes, from stereomicroscope products, used in scrutinizing larger solid objects (as in forensics) and also in high power microscopes used for viewing much smaller objects in more detail. Petrologists (those who study rocks and crystals), use halogen lamps in their microscopes to bring out the structures of thinly sliced fragments. Pathologists examining dead tissue can also benefit greatly from using this bright form of illumination.
Halogen bulbs have a supposed long life. They are also claimed to have a more energy efficient beam. However, the trade-off would be the heat they generate. An illumination mount must be specially constructed to keep the heat away from the specimen observed and special heat sinks built into the illumination mount aides in relieving the microscope's user from this excessive heat.
A halogen light source for microscopy is excellent for viewing hidden structures in substrates of liquid, tissue, and crystals. The heat generated by these bright bulbs may have an adverse effect on living organisms and tissue, so halogen bulbs are not recommended for a standard microscope. However, they will give an overall good performance for specimen viewing when a very bright light source is needed.
Even though LED's were actually developed over a century ago, LED microscope illumination has been used at a high-quality level for little over a decade. At first, LED lamps were prohibitively expensive, but now are very cheap to manufacture and readily available.
The lamp can be used in a wide variety of microscopes. For wide field viewing there can be no comparison to the crisp images that LED lamps provide. Beside their long life, the lamp gives off very little heat, so living organisms will not be harmed by this ideal light source.
Microscopes such as the inverted model would benefit from microscope illumination. Crystallographers need light at a certain wavelength (or even polarized light) and white LEDs, Superflux LEDs, or even color emitting LEDs all have their place in his field.
This microscope illumination has also been developed for fiber optics. The LED's are mounted in a separate box, and the fiber optic line goes to the microscope. This box has settings on the front to either dial down or dial up the light. This is very convenient for the observer, as they have control over the illumination amount.
Fluorescent microscopy leapt ahead because of the invention of this light source. Blue and ultra-violet wavelengths excite fluorophores in special dyes to bring out in sharp relief the structures of the specimen not seen in visible light. This has been a boon for those working in Virology and Histology, for the identification of such organisms as HIV, or HPV.
All microscopes that use electro-illumination will benefit with this lighting. It is cheap, affordable, and long lasting. The brightness depends on the power input, so the amount of energy used is actually in your hands. LED microscope illumination is indeed the wavelength of the future!
To find out about LED light sources and other related products take a look at http://microscopelight.co.uk/