Microscope Illumination Methods
Difference in Light Sources
The light source can differ depending on the microscope being used. It is necessary to select an appropriate light source based on an understanding of the characteristics of each light source.
For optical microscopes
- Natural light (ambient light)
Light from outside is sent to the reflective mirror to illuminate the sample. Direct sunlight must be avoided. An artificial light source, such as fluorescent light, can also be used instead of natural light.
- Tungsten lamp
This inexpensive and readily available lamp, also called an incandescent lamp, is widely used in optical microscopes.
- Halogen lamp
Compared with a tungsten lamp, the halogen lamp is more expensive, has a longer life expectancy, and features a near-white color with uniform brightness.
For fluorescence microscopes
- Mercury lamp
Also known as a high-pressure mercury lamp, this lamp is used as the light source for fluorescence observation to excite a wavelength specific to the fluorescent material. It can provide a strong power over a broad range of wavelengths, from ultraviolet to near-infrared, and can transmit light of a required wavelength using a filter. A wide variety of filters are available for different wavelengths, and a specific fluorescence can be selectively detected when a proper combination of fluorescence dye is being used. Another type of mercury lamp is the metal halide lamp that requires a high-voltage power supply in order to operate.
- Xenon lamp
This type of lamp is generally used as the flashbulb on cameras and features high brightness.
- LED lamp
Because LEDs emit light with a relatively narrow wavelength band, white light can be obtained by combining an LED and a fluorescent material or a combination of multiple LEDs. It features compact size, low power consumption, and long life, but the power may be poor at specific wavelengths depending on how the LEDs are combined.