Infrared has always fascinated both scientists and engineers. It sits just beyond the red end of the visible spectrum, invisible to the naked eye but powerful in countless applications—from thermal cameras and CO₂ lasers to gas monitoring and even medical aesthetics. Yet, one question keeps coming back when people start working with this part of the spectrum: how many nanometers should a filter block before you actually reach “true” far infrared?
This is not just a textbook question. It’s highly practical. The choice of where the cutoff happens—the exact nanometer value where visible light stops and infrared begins—decides whether your imaging system produces a crisp thermal view or a noisy mess. That’s where infrared long-pass filters come into play. Companies like Bodian have specialized in building these filters with precise cutoff points, and their infrared long-pass filters series has become a common choice in industrial, research, and medical fields.
Let’s dive in step by step.
What Defines True Far Infrared in Nanometers
Far Infrared Wavelength Range from 15 µm to 1000 µm
Far infrared (FIR) typically starts around 15 micrometers (15,000 nm) and extends up to 1,000 micrometers (1,000,000 nm). That’s a wide range—spanning from what many would call the “thermal infrared” all the way into the region used by specialized astronomy equipment. Engineers don’t usually deal with the whole span. Instead, they focus on specific slices of this range for practical tools, like laser processing at 10.6 µm.
Transition from Near Infrared to Far Infrared at Longer nm
The infrared spectrum is normally split into near infrared (NIR), mid infrared (MIR), and far infrared (FIR). Near infrared runs roughly from 780 nm up to 2500 nm. Mid infrared extends from 2500 nm to about 25,000 nm. Only beyond that do we enter the “true” far infrared.
Role of Long-Pass Filters in Reaching Far Infrared
Long-pass filters act as gatekeepers. They block shorter wavelengths—including visible light and sometimes parts of the near infrared—while letting through longer wavelengths. For far infrared work, you want the filter to hold back everything below a chosen cutoff, so your sensor, laser, or detector only receives the part of the spectrum that matters. Without such filters, scattered visible light would overpower the delicate signals you’re after.
Why Block Visible Light for Infrared Applications
Prevention of Unwanted Color and Glare
Visible light can create glare on optical components or add strange colors to infrared images. Imagine a surveillance camera trying to detect heat leaks in a building: if stray sunlight enters the lens, the thermal signature may be lost. Blocking visible light isn’t optional—it’s necessary.
Enhancement of Signal Clarity in Detection
Gas detection is a good example. A filter tuned to pass only around 4300 nm makes it possible to “see” CO₂ absorption features. If visible light passes through, the detector would drown in irrelevant signals. Precision comes from silence—blocking the noise lets the real signal stand out.
Improved Imaging for Industrial and Medical Use
In medical beauty devices, such as skin rejuvenation systems, infrared light penetrates deeper than visible light. A properly chosen long-pass filter avoids heating the surface unnecessarily while guiding energy into the tissue layer doctors actually want to target. Patients don’t care about nanometers, but the right filter can mean the difference between safe comfort and an unpleasant burn.
Which nm Cutoff Is Best for Long-Pass Filters
Comparison of Common Cutoff Points from 550 nm to 850 nm
For photographers experimenting with infrared, popular cutoffs include 550 nm, 720 nm, and 850 nm. A 720 nm filter lets through more visible red light, creating surreal false-color images. An 850 nm filter, on the other hand, blocks almost all visible light, giving dramatic black-and-white photos. Engineers in labs laugh a bit at these artistic choices, but the principle is the same in industry: the cutoff decides the look and clarity of the output.
Influence of Cutoff on Image Tone and Contrast
Lower cutoffs allow partial mixing of visible and infrared, producing softer contrast. Higher cutoffs make the scene stark and high-contrast. In spectroscopy or sensing, this translates to clearer separation between absorption bands. Choosing between them is like tuning a radio—set it too wide and you pick up static, set it too narrow and you miss parts of the song.
Selection Based on Photography vs Industrial Sensing
Photographers may choose based on aesthetics, but industrial users choose based on absorption lines or thermal behavior. For instance, a CO₂ laser system absolutely requires filtering at 10.6 µm, not because it looks pretty but because it’s the operational wavelength of the laser. That’s why off-the-shelf “photography IR filters” don’t cut it for industry.
How Does Bodian ILP 10600+ Support Far Infrared Performance
Transmission Above 10600 nm for CO₂ Laser Systems
Bodian’s ILP 10600+ is designed for the classic 10.6 µm CO₂ laser line. At this wavelength, industrial cutting, engraving, and welding machines operate with high power. The filter’s job is to pass that infrared beam cleanly while blocking unwanted shorter wavelengths that could reduce efficiency.
Stability in High-Power Industrial Processing
One underrated detail: heat resistance. These filters must survive exposure to high-power beams without shifting performance. The ILP 10600+ uses thin-film design that holds steady even under long operating hours. Ask any factory technician—they don’t want to pause a production line just to swap out a filter.
Reliable Performance in Precision Laser Applications
Beyond heavy industry, CO₂ lasers are used in delicate tasks like medical surgery and semiconductor processing. In those settings, a filter that doesn’t drift in cutoff wavelength is essential. A fraction of a micrometer off target could affect incision depth or chip yield. The ILP 10600+ provides that stability.
How Does Bodian ILP 5500+ Work in Mid Infrared Range
Transmission Above 5500 nm for Analytical Instruments
The ILP 5500+ serves the mid infrared range, particularly useful for spectroscopy. Many gases, including CO₂ and CH₄, have strong absorption lines in this region. A filter that starts transmitting above 5500 nm helps scientists target those lines directly.
Application in Gas Detection and Monitoring
Consider a refinery or chemical plant. Operators need real-time monitoring of emissions. Placing a 5500 nm long-pass filter in front of a sensor allows selective detection of gases, cutting false alarms from ambient light. It’s like giving the sensor noise-cancelling headphones.
Compatibility with Spectroscopy and Research Equipment
University labs and R&D centers often work with tunable IR sources. Having a stable long-pass filter at 5500 nm lets them isolate experimental conditions. Researchers hate surprises in data. The ILP 5500+ reduces one big variable: spectral contamination from shorter wavelengths.
How Does Bodian ILP 3000+ Enhance Infrared Imaging
Transmission Above 3000 nm for Thermal Sensing
The ILP 3000+ is positioned for thermal imaging and sensing. Wavelengths above 3000 nm correspond to mid infrared heat radiation, which is the bread and butter for thermal cameras.
Benefits for Security and Surveillance Systems
In security, cameras equipped with 3000 nm long-pass filters can detect people or vehicles at night without being blinded by streetlights or headlights. Instead of a washed-out view, the system captures heat signatures. That makes perimeter defense much more reliable.
Practical Use in Medical and Beauty Devices
Surprisingly, filters in this range are also used in aesthetic equipment like skin treatment lasers. By letting through deeper-penetrating infrared while blocking visible light, devices can stimulate collagen or tighten tissue with minimal surface damage. Patients may never know the words “ILP 3000+,” but they feel the results.
How to Choose the Right Bodian Infrared Long-Pass Filter
Match the nm Cutoff to Application Needs
The simplest rule: choose based on your application. CO₂ laser? You need ILP 10600+. Gas monitoring in the mid IR? ILP 5500+. Thermal imaging or medical? ILP 3000+. Picking the wrong one is like putting sunglasses on at night—not only pointless but potentially dangerous.
Evaluate Material Durability and Coating Quality
Not all filters are equal. Bodian emphasizes durability of coatings, which means their filters resist scratching and environmental stress. In industrial settings where dust and heat are constant, that’s a small but critical advantage.
Balance Between Cost and Technical Requirements
Every project has a budget. While it’s tempting to save money with generic filters, cheap glass often fails under stress. A failed filter mid-operation can cost far more in downtime. In this sense, a well-designed ILP filter is an investment, not just a part number.
FAQs
Q1: Is far infrared the same as thermal imaging?
A: Not exactly. Thermal imaging usually works in the 3–14 µm band, which includes mid and part of far infrared. “True” far infrared extends much further, up to 1000 µm.
Q2: Can I use a photography IR filter for industrial lasers?
A: No. Photography filters cut off around 550–850 nm, far too short for lasers at 10,600 nm. Industrial systems need filters specifically designed for those wavelengths, like Bodian’s ILP 10600+.
Q3: What’s the main difference between ILP 3000+, ILP 5500+, and ILP 10600+?
A: The cutoff wavelength. ILP 3000+ transmits above 3000 nm, ILP 5500+ above 5500 nm, and ILP 10600+ above 10,600 nm. Each serves different industries—from medical beauty to spectroscopy to heavy-duty laser cutting.
Beijing Bodian Optical Tech. Co., Ltd.
