The best light source for your microscope is going to largely depend on two primary factors: the microscope you’re using and the reason you’re using it. To fully understand why a particular light source is best, you need to understand the way that each light source works. Knowing how other scientists use each source in their microscopy applications can also be critical.
The four most common microscope light sources include Arc Lamps, LEDs, Incandescent (Tungsten) Lamps, and Halogen Lamps.
Arc Lamps produce an electric arc (also called a voltaic arc) between two electrodes. They’re used in fluorescence microscopes, usually relying on either mercury or xenon ions to produce a high-intensity white light, similar to lightning. Many things can cause these plasma-based light sources to become unstable, causing the light itself to flutter or flare. However, if you handle them properly and use a reliable power source, arc lamps are more than capable of producing the results you’re looking for. When you use an Arc Lamp, keep in mind that its quality will visibly deteriorate over time and that it can be influenced by unstable power sources and nearby electric fields, among other things.
As we mentioned before, Arc Lamps are used in fluorescence microscopes. Fluorescence microscopes are used to study both organic and inorganic materials, especially if those materials are so complex that they can’t be thoroughly studied under a conventional, transmitted-light microscope. You’ll typically find fluorescence microscopes in scientific laboratories, so if you work in a setting where fluorescence microscopy is applicable, an Arc Lamp light source might be the right choice for you.
Light-emitting diodes (LEDs) are another commonly used light source in fluorescence microscopes, particularly in widefield fluorescence microscopy applications. LEDs require little power to operate, known for their ability to turn energy into light without generating much heat.; in fact, the wavelength of light that these bulbs emit is so narrow that it can run for days at a time without producing anything hot enough to burn the microscope user. Additionally, LED bulbs have long lives, lasting more than 40,000 hours! Does it all seem too good to be true? Unfortunately, nothing is perfect and there are some potential pitfalls to using LEDs for fluorescence microscopy. First, even though the bulbs are long-lasting, they’re often built into the microscope in such a way that they’re a little inconvenient to replace. Second, the color of the emitted light can sometimes interfere with the appearance of certain samples.
If you understand this or, even better, know how to mitigate these risks, and if you’re looking for a light source that saves both power and energy, a LED bulb might be for you, even if you have no interest in fluorescence microscopy. After all, nearly all microscopes function well with a LED light source, including compound microscopes, stereo microscopes, and digital microscopes! LEDs are versatile in their applications, so it’s definitely worth exploring no matter what microscope you have or how you plan to use it.
Incandescent (Tungsten) Lamp
Incandescent Lamps are also called tungsten lamps because their wire filaments are made from tungsten metal. Incandescent microscope bulbs are similar to household bulbs in that they’re made of glass, a chemically inactive gas, and a conducting wire that turns a DC current into light. Tungsten bulbs provide a reliable source of illumination, which is one of the main reasons why incandescent lamps are the most common light source found in microscopes. Another reason is that they are relatively inexpensive and easy to find, available in a variety of shapes and sizes.
Because incandescent bulbs are the most common bulb used in microscopy, most optical microscopes are built to accommodate them. One of the downfalls of tungsten lamps is that they can reach very high temperatures, sometimes causing serious burns if they aren’t handled with care. Tungsten bulbs are most commonly found in compound microscopes, which can be used for a wide variety of applications, ranging from medical surgery to the study of rocks and minerals. Unless you’re using your microscope for a highly advanced purpose, an incandescent lamp can serve you just fine!
Technically speaking, a Halogen Lamp is a subcategory of incandescent bulbs. One trait that sets it apart is the layer of quartz it uses to protect the glass from becoming too hot; another is the bromine gas surrounding the tungsten filament. Bromine absorbs the tungsten metal as it evaporates over time, which then allows the bulb to operate at a lower amount of power and last a longer time than regular incandescent bulbs. However, both incandescent and halogen lamps can be modified with dimming switches to control the amount of illumination they provide.
Because halogen bulbs typically last longer than their traditional incandescent counterparts, they tend to cost more. Halogen lamps are just as versatile and useful as normal incandescent lamps, but if you’d like a tungsten bulb that costs more upfront but saves money in the long term, we recommend using a halogen lamp.
As we said before, with so many options available, the illumination source you need depends mostly on the microscope you’re using and your desired application. Carefully weigh your options from a practical, technical, and financial standpoint and choose the light source that best serves you and your microscopy application.