4 Common Types of Microscope Light Sources
Depending on the type of microscope you have, and the most common reasons you use it, you may be presented with a handful of options when looking for a light source. Ambient light from lamps and the sun may have sufficed in the past, but they don’t hold a candle to the range of bulbs and diodes diodes available for microscopy today. When it comes to research, inspection, or educational applications, it’s essential to have illumination appropriate to the task for both viewing and imaging. Below, we’ve assembled a list of four common types of microscope light sources, and the factors to consider before determining which one is right for your work.
1. Incandescent Lamps
Also called tungsten lamps, in reference to the metal used for its wire filament, this type of microscope bulb is comprised of glass, an inert gas and a filament that turns a DC current into light. These thermal radiators are designed similarly to traditional household bulbs, and provide a continuous, reliable source of illumination. Incandescent lamps are the most common type of bulb used in optical microscopes. They are relatively inexpensive and easy to find in many shapes and sizes.
Most optical microscopes have built-in housing to accommodate incandescent bulbs. It’s very important to read the manufacturer’s instructions and only use bulbs with voltage and power ratings that were intended for that particular microscope. If your microscope does not have an internal light source, you can purchase an external source, many of which also use incandescent bulbs. Whether you use an internal or external incandescent lamp, take care to carefully read the instructions on how to replace microscope light bulbs. Tungsten-based lamps can reach very high temperatures and can even cause serious burns if handled inappropriately.
Technically a subcategory of incandescent bulbs, halogen bulbs use a layer of quartz to protect the glass against higher temperatures and bromine gas to surround the tungsten filament. Bromine absorbs the tungsten as it evaporates from the filament over time, creating a bulb that can operate at a lower wattage and last a lot longer than the typical incandescent light. Both incandescent and halogen lights can be hooked up to dimmer switches to control the amount of illumination. Tungsten-halogen bulbs typically last about twice as long as traditional incandescent bulbs, which is why they sell at a higher price point.3. Arc Lamp
Arc lamps are lights that produce an electric (also called voltaic) arc between two electrodes, following the same basic principles of lightning. Modern arc lamps rely on mercury or xenon ions to produce white light at a rather high intensity for use in fluorescence microscopes. There are several factors that can lead to instability in these plasma-based light sources, which can cause the light to flutter or flare. With proper use and a reliable power supply, arc lamps can produce the results you’re looking for. However, their quality does visibly deteriorate with age, and they can be sensitive to outside influences such as an unstable power supply or a nearby electromagnetic field.
Light emitting diodes (LEDs) are commonly used in widefield fluorescence microscopy. LEDs require relatively little power to operate, are known for their long lives and efficiently turn energy into light without generating much heat. Many microscope LED bulbs can last more than 40,000 light hours, which is remarkable in comparison to incandescent bulbs. They also emit a narrow wavelength range and can run for days at a time without producing enough heat to burn the user. If this all seems a little too good to be true, it’s because LEDs have some downsides when it comes to fluorescence microscopy. The glaring and most common issue is that they are often built into the microscope in such a way that they can only be replaced by factory warranty or repair. The second issue with LEDs is their spectrum. They emit bright white or even bluish light that can interfere with the appearance of certain samples.
When it comes to choosing a microscope light source, your choices are first narrowed down based on the type of microscope you use. From there, you can determine whether longevity, spectrum, accessibility, or stability are your top priorities. Lastly, it all boils down to personal preference and what accessories you feel the most comfortable operating. This list is just the tip of the iceberg. With so many options to explore, you’re bound to find the right illumination that fulfills all your requirements.
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