LED light sources can be customized to provide the correct quality of light for professional tasks.
Currently in the microscope, the existing light source is a quartz-halogen incandescent lamp, and LEDs are currently entering the microscope because the halogen source typically dissipates 50W-100W. However, it can be seen that halogen sources are still very advantageous, they are essentially black body heat sinks.
This means that they produce a continuous spectrum without any bumps, so any object of any visible color can be seen and any visible color can be separated by optical filtering.
Clive Beech, component manager of British LED manufacturer Plessey, said, "The benefit of halogen is that it is a good broad-spectrum source. The spectrum is very uniform and the color is very good."
Each has its own strengths
Optical microscopy is not entirely complete. Some microscopes do the same job every day, such as counting white blood cells, requiring a narrow range of illumination. Others are generic, in which the required number of lighting options is "more". The observer may look directly at the eyepiece or connect to the monitor of the microscope camera.
Researchers sometimes need excellent, accurate color rendering performance, requiring high contrast between what they are looking for and what they are not interested in, and therefore requires the best combination of spectral and illumination directions.
The first problem with halogens is to protect the sample from heat. Beech said: "It comes with high load of infrared light, which is harmful to any tissue sample or organic material, so you have to filter it out."
The LED avoids this layer of filtering because the standard blue core plus phosphor technology does not produce IR. Plessey optical designer Samir Mezouari said, "Most [LED companies] can simulate blackbody emission spectra. But the challenge is how to get the best performance."
Sufficient optical power is also in place. Beech said: "Our standard white LED is 12V 8W 1000 lm, and the lens is available in a 7x7mm package.
The four attachment points of the device are tiled flat on a single chip with virtually no gaps between the emitters, eliminating artifacts.
LED brings change
Although more current is required, large-size chip LEDs are also possible, requiring an increase in the size or number of die bond wires. These are potential problems with microscope illumination, and even if Kohler illumination minimizes this effect, residual images of the source structure may be superimposed on the view of the object.
Even with the necessary bonding wires, the LED source is brighter than the halogen lamp. For very sensitive samples, LEDs can be micro-flash photography to further reduce heat and infrared.
Beech said: "You can't remove the halogen to reduce the energy input, but you can use the LED. You can shoot the light with the camera that is always on, and the sample that can't be shot with the halogen bulb can be imaged by the LED."
It is also easier to use space for LED lighting. For example, Leica allows the LED ring to pass through the objective lens of a reflective microscope to achieve surface characteristics by producing light from only one angle.
Due to the long life of the LED, the LED can be permanently built into the optical instrument, eliminating the need for rearrangement and calibration steps required to replace the halogen bulb, saving space, eliminating the need for finger space and less heat dissipation. .
Contrast enhancement
The first step is to replace the halogen with a continuous spectrum of LEDs. For contrast enhancement, some microscopes include switchable optical filters that can be replaced with LEDs of many different wavelengths.
Beech said, "You can't always want to image with a uniform spectrum. For example, with blue light, the red light sample composition will become darker, so you can increase the contrast."
He added, "With LEDs, you can make a broad spectrum of phosphors. Especially for pathology, I will choose the wavelength."
Mezouari said: "Imagine red, green, blue, white LEDs, emit some broad spectrum, peaks with specific wavelengths. Then, for example, you can turn off the red and find the spectral formula for the specific sample you want."
Camera digital image processing is an important part of the microscope, and Mezouari believes that combining images taken at different wavelengths allows for highly enhanced images. Which wavelength of LED is chosen depends on the job at hand, but if using a camera, Beech recommends matching the red and green to the RGB filtering of the blue and camera chips.
In extreme cases, higher resolution can be provided by using only the short-wavelength (blue) light that is available from the LED or that filters out most of the halogen energy. There is also some evidence that long-term exposure to intense blue light can adversely affect the human eye.
LED light source
Before the science becomes clearer, in the case where the operator may expose himself to strong light, then the precaution may be to limit the light source to a halogen analog or green wavelength or longer wavelength. For severe short-term exposure, there are already light biosafety standards.
A complete cancellation of spectral illumination can be a mistake because a sample may only include a single color material that is inconsistent with the light source.
For multi-wavelength LED sources, the light must be combined in some way. Mezouari said: "You can use a tiny LED array with a small diffuser to get hundreds instead of thousands of lumens, but it's enough."
“If you have enough space, use a separate LED and a few centimeters of mixing rods. Or if you only have red, green and blue, you can use a prism reflector to mix and sometimes add a mixing rod.â€
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