Light wavelength
Ultraviolet and infrared light Among wavelengths invisible to the human eye, wavelengths shorter than visible light are called "ultraviolet light" and longer wavelengths are called "infrared light". (See the figure on the previous page.) Since each wavelength has different visible characteristics, it is necessary to use different wavelengths depending on the object.
"Light" is a class of waves called electromagnetic waves. The range of this light that the human eye can perceive is called "visible light" and extends from about 380 nm to 780 nm (nanometers). The wavelength range used in imaging is even wider than visible light, ranging from ultraviolet to infrared.
Electromagnetic waves
Exposure of certain objects, including phosphors, to ultraviolet light causes a fluorescence phenomenon (excitation) that absorbs the ultraviolet light and emits light with a longer wavelength. This allows the position of objects that are difficult to recognize with visible light to be captured more easily. Image captured by ultraviolet light
0.0001nm 0.01nm
10nm
1000nm
100m
0.01cm 0.1cm 1cm
1m
Ultraviolet rays
Radio Waves
Infrared rays
Gamma rays
X-rays
Visible light
Ultraviolet light（UV light）
Visible light
Ultraviolet light（UV light）
←Short wavelength
Long Wavelength→
Visible rays
Crumbs are mixed with foreign objects of the same color, which cannot be distinguished by visible light.
Unable to tell where the gear is coated with grease.
Grease is protruded and the applied area is clearly recognizable
Crumbs stand out and become brighter, while foreign objects can be kept dark.
400nm
500nm
600nm
700nm
Wavelength and Resolution
It can transmit through specific objects. This allows detection of substances within the object that are not visible with visible light. It can also darken and detect areas that contain more moisture than their surroundings, due to the absorption properties of moisture in a specific wavelength range of infrared light. Image captured by infrared light
The wavelengths of visible light are relatively short for blue and violet (short wavelengths) and longer for red and orange (long wavelengths). This characteristic leads to differences in refractive indices in lenses, and especially in the case of lenses with high magnification, the wavelength of the light source has a noticeable effect on the resolving power of the image. δ(μm)＝0.61 × λ ／ NA （λ=wavelength, NA=lens aperture) Resolution is expressed by the above formula, but if the same lens (same NA) is used, the longer the wavelength, the greater the spatial resolution=less finely resolved. If you want to image a small workpiece at high resolution, it is necessary to carefully select the wavelength of the lighting and the numerical aperture of the lens.
visible light Red
Infrared transmittance: Distinguishes between wood grain and cracks
Moisture detection: Water droplets on tablet confectionery
Sunlight
orange yellow green blue indigo purple
Visible light
Visible light (blue)
Infrared light (IR light)
Infrared light (IR light)
Prism
Due to differences in refractive index, sunlight is divided into bands of color as it passes through a prism
Infrared transmission + moisture detection: Water droplets of dried wakame seaweed
Infrared transmission + moisture detection: Scratches on eggplant
Visible light
Visible light
Infrared light (IR light)
Infrared light (IR light)
←Short wavelength
Long Wavelength→
Visible rays
Infrared rays
470nm(Blue)
630nm(Red)
850nm(Infrared)
1200nm(Infrared)
Comparison in infrared light Left: Oil / Right: Water
Short wavelength
Long Wavelength
1200nm
1450nm
1650nm
Visible light (Red)
Natural light
There is no difference under natural and visible light, but as we move to longer wavelengths, the water appears blacker and the difference becomes clearer.
188
189
Made with FlippingBook Ebook Creator