The human eye is sensitive light in the range 400nm (blue) to appx 750nm (red). Over 750nm is usually considered Infra Red - this is derived from the Latin 'infra' or 'below' to give the meaning 'below red'
Near Infrared is considered to be 750nm-1400nm and is invisible to the human eye. The 'light' from such a source is absorbed and reflected in the same way normal visible light is. Generally speaking a surface that absorbs IR will appear black on a NIR camera and surfaces that reflect NIR will appear white.
Due to the difference in frequency between infra red and visible light, some surface or materials will appear to be a different colour when viewed under IR. It is very noticeable with blacks and some materials will even become transparent under IR. One example of transparency is with 2 layers of exposed and developed photographic film - dark brown and opaque under normal light it becomes clear transparent under NIR.
As seen in these two photographs, the contrast between the the blacks is obvious. Not a disadvantage if you where seeking cover near or against a concrete wall while wearing black that shows up white under NIR. This would be a definite disadvantage if you where hiding in a dark corner or had mixed IR signature equipment as in these photographs.
Compare the photographs of the DPM camouflage suit under NIR - this particular uniform is a genuine Army issue suit and it retains its disruptive pattern under NIR
Exposed and developed 35mm film is transparent under NIR. It can also be used as a poor quality filter to let through IR and block normal visible light.
This type of filter has been used to lower the exposure on Nightshot cameras that have been Factory set to over expose in daylight. This is because some clothing becomes transparent in bright sunlight when viewed in NIR
A surprising number of other materials become clear transparent under NIR
NIR and IR are employed by various security systems to aid identification and observation.
The UK has the most police CCTV surveillance cameras per capita than any other country, don't try to hide behind dark sunglasses!
Would they really use IR cameras?
The following photographs compare various DPM materials and Armed Forces equipment in Visible and Near IR.
It has been found that most genuine military clothing and equipment does not change its properties when viewed in NIR, whereas the cheaper and 'made for Airsoft" clothing and equipment is unpredictable.
As more night vision equipment becomes available and older generation scopes are sold off at a reduced price, they will become a common tool used on Airsoft night games. It will be a great disadvantage for the person who's uniform glows white when they are using dark cover. The same for the person who stands against a concrete wall wearing clothing that appears black in NIR. Choice of cover will have to be taken with the knowledge of your IR visibility. The easy way is for the clothing and equipment to have the same properties in visible and IR light.
Thermal imaging sights and cameras are a different ball game - Camouflage under FLIR is difficult but not impossible to achieve but as usual for every measure there is a counter measure. A simple method to hide from 4th Generation night vision scopes is the high end "Space Blankets" - not the paper thin marathon finish sheets. Once the heat signature is reduced normal camouflage techniques are used to provide the advantages required. - not too much on this for obvious reasons.
Normal Army issue DPM combat jacket issued 1982-1990. The jacket retains some disruptive pattern under NIR
The difference in black dye is noticeable on the sewn name tag - it is almost a complete shade reversal under NIR
This is a store bought "Army" jacket that does not retain any pattern under NIR
The black dye used reflects NIR showing up white when viewed
The black helmet liners - dayglow white when viewed in NIR
The synthetic material reflects IR very well
Black anodizing seems to reflect NIR
I have yet to find a black anodized item that shows black in IR
Black powder coat and black paint remains black.
As can be seen in the captures, the red dot sight on the Airsoft MP5 is almost mirror like when viewed under NIR
An ongoing project to find a simple effective camouflage technique to suit the range and speed of airsoft and paintball skirmish games. The intention of the camouflage is to buy you enought time to get the first shot off and then move, not to remain undetected scout/sniper style.