 Getting The Right Material
Electromagnetic Spectrum
Only a small part of the electromagnetic spectrum is visible light ranging from blue/violet light to red light. Ultraviolet light has a higher frequency than blue light, whereas infrared has a lower frequency than red light. Both ultraviolet and infrared light are invisible to the human eye.
All objects above absolute zero (-273 degrees) emit radiation, some of which is infra-red. Depending on temperature and emissivity, most objects in the world can be thermally imaged.
Visible
Visible light extends roughly from 400nm (violet) to 700nm (red). There is obviously some overlap but as a guide the colours fall into these regions:
• Violet: 400-430 nm
• Indigo: 430-450 nm
• Blue: 450-500 nm
• Green: 500-570 nm
• Yellow: 570-590 nm
• Orange: 590-610 nm
• Red: 610-700 nm
Infra-Red
In comparison to visible, the infra-red region is quite large and has the following regions. Note that 1µm is 1000 times longer than 1nm.
• Near (NIR): 0.7 to 1.5 µm
• Short wavelength (SWIR): 1.5 to 3 µm
• Mid wavelength (MWIR): 3 to 8 µm
• Long wavelength (LWIR): 8 to 15 µm
• Far infra-red (FIR): longer than 15µm
A common misconception regarding IR cameras is that they can see what you can see, this is not completely true.
Glass and Perspex are completely transparent in the Visual wavelength; however to an Infra Red Camera they are completely opaque. The images below show examples of data gathered through differing materials, in this demonstration images were taken without optics, through glass and finally through Germanium.
Manufacturers place too much importance on providing IR window material with a very high infrared transmittance value; more consideration must be given to the environmental and operational conditions in which the window will be used, you want a window that will be functional for the life of the panel in which it is fitted, therefore never trade off mechanical properties for higher infrared transmission rates, you don’t need them, you do however want a window that lasts.
The following pages contain information regarding the materials that are used by G M Tech and the current range of IR windows available.
View Facts Sheet
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