NIR – Myth or Reality?

What is NIR? NIR stands for Near-Infrared Radiation. The purpose of this article is to provide a basic understanding of the impact of near-infrared radiation on the manufacturing, use, and maintenance of military clothing and equipment. We are not professionals in the fields related to electromagnetic radiation, but we understand on a practical level how these things affect our work and the needs of the end-user.

This article is not groundbreaking scientific research but a down-to-earth response to a series of questions that might otherwise be difficult to find answers to. We’ve separated the practical elements from rocket science and the facts from misconceptions, packaging it all into an easy-to-read format.

Abbreviations and terms used in the text:

Infra? Ultra? The visible part of electromagnetic radiation, or the light visible to the human eye, occurs within the wavelength range of 380-750 nm. Red is at the upper end of this spectrum. However, "infra" in infrared means something that is "below" or "under," as the term refers to frequency, which is inversely proportional to wavelength. Similarly, "beyond" the violet at the other end of the spectrum is ultraviolet, which has a shorter wavelength but higher frequency. Still with us? Good!

• IR: Infrared, meaning all infrared radiation, is a commonly used but very broad term
• NIR: Near-Infrared, invisible "light" to the human eye
• LWIR: Long-Wavelength Infrared, also known as thermal radiation – invisible, but felt as heat

In addition to these, there are other classifications for infrared, but we won’t dive into those this time.

NIR and LWIR and Why They Are Completely Different

In this context, NIR refers to the invisible light that is seen with a night vision (NV) device. LWIR, on the other hand, means thermal radiation, which is seen with a thermal imager. These two are completely different and should not be confused with each other. An NV device cannot see the LWIR thermal signature, and a thermal imager cannot see NIR light. There are devices where both sensors are combined, and the image is shown as a combination of both, but they remain two entirely different phenomena.

The NIR image produced by an NV device is essentially a black-and-white (or black-and-green) version of the visible world. The image from a thermal imager (LWIR) reveals deviations in temperature (warm objects vs. cooler surroundings). Neither is perfect; both have their strengths and weaknesses. Protection from thermal imaging is a separate art form, and we won’t delve into it here.

What Can Be Seen in the Dark?

NIR light is invisible to the naked human eye, and it almost always accompanies all natural and artificial light sources (the sun, electric lights, etc.). In principle, wherever there is even a little visible light, there is also NIR light. With an NV device, you can also use an IR illuminator – although these can reveal the user's position to counter-surveillance since the illuminator's NIR light, infrared laser pointers, and similar devices are also visible through the opponent's NV device.

The NV device Detects Different NIR Reflections

A night vision device "sees" both visible light and the invisible NIR light and presents its observations in a form visible to the human eye on a display. In dim light, the image produced by the NV device consists of both visible and NIR light. In a pitch-dark environment, using artificial IR illumination, the image displayed by the NV device consists solely of NIR light. The more the image shown by the NV device is based on NIR light, the more it may differ from what the naked eye sees.

The NIR world seen through a NV device is monochromatic, meaning single-colored or "black and white" (though there are exceptions with new innovations). The NV device detects only how strongly or weakly different surfaces in the environment reflect NIR light. Non-reflective areas are displayed very dark on the NV device’s screen, while highly reflective areas appear very bright.

Different materials and surfaces such as tree trunks, rocks, leaves, and snow reflect NIR light in various ways, some more and some less. In a built environment, artificial materials and other extremes further complicate matters.

The character in the center is wearing a wool uniform with M05 woodland camouflage fabric on the reinforcements, hem pockets, and hood. The shelter fabric in the foreground is British Basha DPM camo. The shelter fabric in the background is DD Tarp 3x3 olive green with a black shotgun on top of a Berghaus Crusader rucksack.

Camouflage Against Night Vision Surveillance

A common and entirely incorrect misconception is that equipment "must not reflect NIR light." No, it’s not that simple. To hide from NV device surveillance, equipment must reflect NIR light in just the right way, with the same intensity as the environment it’s trying to blend into. In practice, the camouflage pattern should look like a black-and-white version of how it appears to the naked eye when viewed through an NV device, making it "NIR-compliant."

There is no such thing as an actual "NIR shield." There is no magical substance that can be applied to a finished garment or piece of equipment that will make it suddenly invisible to an NV device (or thermal imager, as is sometimes claimed...). Protection from night vision surveillance is achieved by using precisely developed dyes in the camouflage pattern that reflect NIR light at exactly the desired intensity.

Different materials require the development of individual dyes. What works on one material may not work on another, and then there are the compatibility challenges of different mixed materials. For example, printing a four-color NIR-compliant camouflage pattern onto a cotton/polyamide blend fabric can be a significant challenge.

The Finnish Defence Forces have set strict requirements for the NIR reflectance values of the colors in camouflage uniforms and equipment. These are then tested in laboratories using various instruments to ensure that the materials perform as they should. To ensure the NIR compatibility of our military-use Särmä TST clothing and equipment, we use materials and components manufactured by reliable suppliers according to the Defence Forces' requirements. "Visual" quality control is done using night vision devices to see the product in the "light" that actually matters.

NIR-compatible Särmä TST L5 Thermal Patrol Coverall and CP15 combat backpack appear as shown when viewed through a night vision device. The person is visible, but not due to a lack of NIR compatibility. Camouflage and protection from detection involve more than just NIR issues.

Beware of NIR Hazards

In military equipment, the NIR characteristics of materials are very important, as important as camouflage against naked-eye surveillance. In civilian equipment, this doesn’t matter at all, and developing dyes to achieve the desired NIR reflection is an expensive endeavor. This is one reason why civilian materials are cheaper than their military counterparts.

Thus, it’s understandable that "cheap manufacturers" of military-style gear and other civilian products use materials whose NIR properties have not been given any consideration. These items often stand out as bright white or pitch black when viewed through an NV device. Camouflage patterns can blend into a light-colored mess. Often, there are sharp contrasts between fabrics and webbing, and a civilian backpack covered with PALS webbing might look like a bright white sack with pitch-black stripes under an NV device.

Even small pieces of equipment and details can pose a threat. Something as minor as using the wrong type of Velcro on a jacket sleeve can act as an "NIR reflector," which, when moving, can be visible from a distance. In the wrong place at the wrong time, this could be fatal.

In the picture, on the sides are NIR-compatible green and snow camo CP15 Backpacks. The background is dirty snow. In the middle is a black assault pack, whose fabric does not match the color of the straps when viewed through a night vision device.

In the background is a Särmä TST Combat Pack (NIR-compatible according to Defence Forces specs), with a Tasmanian Tiger Tac Pouch 4 on top, the photo was taken through a PVS-14 night vision device using the device's own NIR illuminator. As shown, the contrast is quite pronounced. Especially in motion, even a small "NIR reflector" can reveal the user from a long distance when detected.

Maintenance of NIR-compliant Material

Equally as important as ensuring that military clothing and equipment are NIR-compliant is making sure this effect is maintained throughout the lifecycle of the item. This requires proper maintenance, which is why, for example, the Finnish Defence Forces prohibit the home washing of their camouflage uniforms. Around this prohibition, all sorts of legends have formed. Among the many rumors, perhaps the strongest misconception is that the "NIR protection substance" wears off in the wash and that this mythical "protection substance" is added back to the clothing in the Defence Forces' maintenance chain after washing. Nope, that’s not the case. The reason for the Defence Forces' ban on home washing of camouflage uniforms lies in the optical brighteners used in many laundry detergents and fabric softeners:

"Optical brightener is a fluorescent substance that makes textiles or paper appear whiter than they actually are. The molecules of fluorescent agents used in textile detergents can convert the Sun's invisible ultraviolet radiation into visible white light with a short wavelength. This masks the yellowed shade of an originally white garment that has yellowed over time. Colored garments also appear brighter." (Source: Tieteen Kuvalehti magazine.)

The purpose of optical brighteners is to make clothing colors look appealing. Unfortunately, this has very harmful effects from a military perspective when viewed through an NV device. Fabric "ruined" by optical brighteners may reflect more NIR light than intended, meaning, for example, a camouflage uniform might no longer provide the intended protection from NV device surveillance. Not good.

How Should Military Clothing Be Washed?

There was no readily available information or answers, so we conducted a simple experiment. We washed pieces of fabric meeting the Finnish Defence Forces' NIR requirements in different detergents, rinsed them, allowed them to dry, and then checked the effects using NV devices. The results of this test were quite inconclusive, as we really couldn’t induce any change by just one washing cycle. Perhaps the NIR-detrimental effects take a few cycles and an ample amount of optical brighteners to happen. But anyway: Any washing of NIR-compliant stuff should be done carefully and is done at your own risk!

To be on the safe side, here is a few good rules of thumb of common wisdom concerning NIR-maintenance:

A Few Good Rules of Thumb

• The more "color-this-and-that" the detergent is, the worse it is
• Bleaching agents and detergents for whites are generally very bad
• The more natural the detergent, the safer the choice
• Detergents marked with an allergy label should not contain optical brighteners

Summary

1. NIR and LWIR (thermal radiation) are completely different things. Confusing them is dangerous.

2. A garment does not "protect" against NIR; it is made to blend in by reflecting NIR at a certain intensity.

3. A piece of camouflaged gear should blend into terrain similarly when viewed with the naked eye as well as through a night vision device – this is what NIR-compliance means.

4. Choose your detergent wisely, and avoid those with optical brighteners.

And Most Importantly

If you didn’t understand what this article is about, don’t worry – it probably doesn’t concern you, and you can continue to sleep peacefully at night.