Measuring IR Light and Near-IR Light
Infrared (IR) light emits a broad range of non-visible wavelengths in the electromagnetic spectrum. Applications for infrared, including near-infrared, are defined by the respective IR bands during output. For example, LIDAR (Light Detection and Ranging) equipment uses 1,000 nm and 1,550 nm IR bands while surveying an area. In the military sector, 850 nm, 1,060 nm and 1,500 nm (and up) are used in IR laser range detection systems.
It is important to consider that measuring infrared light and using IR to measure the thermal properties of a surface are two completely different practices. The tools below are limited to measuring IR wavelengths and IR spectral properties.
IR viewers are handy tools that are designed for locating infrared illumination in the target area before measuring. They are usually small, handheld devices that incorporate a viewing mechanism, similar to a camera. Such units are capable of viewing a wide range of wavelengths, from 350 nm to 2,000 nm. Powerful lenses and filters can be used to enhance IR detection by blocking out or limiting a specific range of IR bands. For low intensity IR beams, the operator would need to observe special viewing practices for accurate readings, including: reduction of external background interference, reliance on low IR absorption surfaces (such as metallic surfaces- paper materials are known for absorbing IR bands), distance from the target object or area and the application of robust IR filters.
Optical Spectrum Analyzer
Optical spectrum analyzers can be used to measure IR and near-IR bands, ranging between 800nm and 1,600 nm. Such systems are capable of measuring wavelength emissions from a wide range of light sources, such as lasers, laser diodes and LEDs. During operation, an IR illuminator (or other light sources) is emitted to a receptor. A fiber optic cable then takes the signal and pushes it through a spectrometer, where it is processed. The type of connector varies, depending on the specific IR wavelength being tested. An optical spectrum analyzer software is used to graph and display the results generated by the spectrometer. Using the software, one can pinpoint the exact IR bands present in the light source sample.
An infrared spectrometer is a device that measures the absorbance and transmittance of an interaction between a sample and IR wavelengths. This is a useful tool for measuring IR, because it allows one to see how IR affects chemicals, objects, liquids and surfaces. For example, if you have an IR emitter, you would want to see how the range of peak IR wavelengths that the illuminator is pushing out affects objects or materials it comes in contact with. IR spectrometers are mostly used in chemical analysis, medical testing and forensic analysis. Most infrared spectrometer instruments are used in the lab, but there are also portable variants that can be used on the field. One of the main drawbacks with using such machines is the requirement of small samples for testing.
Infrared Detectors and Digital Radiometers
Radiometers are typically used to measure non-visible light outside of the visible spectrum, which includes ultraviolet and infrared. Such tools measure wavelength ranges, as well as the peak wavelength ranges of the light source. IR radiometers are mostly utilized for measuring thermal energies. However, filters and digital variants can be used to capture spectral readings of IR light. For near-infrared irradiance, compact detectors may be applied for specific spectral wavelength measurements.
Many people assume that a regular lux meter can be used to measure IR intensity. Unfortunately, this is not recommended, and attempting to do this using an IR light source will likely generate a zero reading on the device. This is because lux meters are designed for measuring visible light. Since IR is non-visible, a standard lux meter will not be sufficient for such wavelengths outside of the visible light spectrum. From another perspective, since the human eye is not sensitive to IR bands, it is not possible to define a lumen for IR wavelengths.
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