Infrared backlighting is an integral part of most modern video surveillance systems, allowing you to get a clear image in total darkness. However, in some cases, the glow of LEDs can give the location of the hidden camera or create unwanted glare, unmasking the object of observation. Understanding the Physical Principles of Work IR emitters It is necessary for their effective masking without loss of functionality of the device.
There are several proven ways to minimize the visibility of glow to the human eye while maintaining the efficiency of night photography. It is important to consider that the complete elimination of the visible spectrum of glow often requires compromises in range or image quality. In this article, we will discuss the technical and physical aspects of how to do the job. night vision It's as subtle as possible.
The main problem is that many cheap LEDs not only emit in the invisible range, but also have a small “shelf” in the visible red spectrum. Exactly this. flashlight And it gives out a camera in the dark. To solve this problem, it is necessary to approach the issue comprehensively, using optical filters and the correct installation of equipment.
The principle of operation of IR illumination and visible glow
Most surveillance cameras are equipped with LEDs operating in the wavelength range of 850 nm. This spectrum is not chosen by chance, as it provides the best sensitivity of the matrix during night shooting. However, the human eye is able to detect a faint red glow at the edge of the visible spectrum, making such devices noticeable at night.
More advanced models use emitters with a wavelength of 940 nm and above. Such devices are almost completely devoid of visible glow, since their operating range is deeper in the light. infrared. However, it is worth considering that the sensitivity of the matrices to this range is lower, which may require more powerful emitters or lead to a decrease in the range of night shooting.
⚠️ Warning: Using too powerful filters can completely block a useful signal, making nighttime shooting impossible. Always test for changes in real light.
The difference between visible and hidden glow is often the quality of the components used. Cheap LEDs often have a wide range of radiation, capturing the visible red area. Professional equipment is deprived of this disadvantage due to the use of high-quality crystals and built-in filters.
For maximum stealth, choose cameras labeled "Black LED" or "No-glow" that use 940 nm diodes.
Use of optical filters for masking
The most effective technical solution to the problem of visible glow is the installation of specialized optical filters in front of the lens or directly in front of LEDs. These filters work on the principle of cutting off waves of a certain length, passing only the necessary infrared.
Filters are divided into two main types: pass and cut. For our task, pass filters are suitable, which block visible light (up to 700 nm) and allow IR radiation to pass through. A quality filter must have a high optical density in the visible area to completely hide the red glow of the diodes.
| Type of filter | Wave length of the cut-off | Visibility of glow | IR permeability |
|---|---|---|---|
| Standard red. | 600 nm | Tall. | Low. |
| Infrared 720 | 720 nm | Medium | Medium |
| Infrared 850 | 850 nm | Low. | Tall. |
| Infrared 900+ | 900 nm | Absent. | Medium |
When installing a filter, it is important to consider its location. If you stick the filter directly on the LEDs, you can achieve an effect when the glow is visible only at point-blank range, but not at an angle. However, it is more correct to install a filter in front of the entire optical camera system to cut off the parasitic illumination from the camera. lens and the interior elements of the body.
Where can I get the filters?
Specialized IR filters can be found in photo equipment stores, radio electronics or ordered from optical glass manufacturers. Filters from old webcams or remote control are often suitable.
Mechanical masking and shielding
Physical masking of the radiation source is a simple but neat method. Its essence is to create a barrier that hides a direct view of LEDs, but misses IR rays. For this purpose, materials that are opaque in the visible spectrum, but transparent to the infrared.
One of the popular materials is a certain type of black plastic or a special tinting film for windows. Some types of high-dimming car tinting can effectively hide the red glow by letting in enough IR waves to allow the camera to operate. Before sticking the film, you need to check its transparency using a remote control.
- 🎥 Use a multilayer structure: black grid + IR transparent glass.
- 🔦 Direct the LEDs at an angle so that a direct beam does not hit the lens.
- 🛡️ Screen the back of the diodes so that light does not scatter inside the case.
It is important not to overdo it with shielding, as this can lead to overheating of LEDs. Heat vent In compact chambers, it is often designed for free air circulation. Closing the vents or tight diode winding can shorten the life of the device.
☑️ Checking the quality of the masking
Sensitivity and operating mode settings
Modern video surveillance systems, such as Hikvision or DahuaThey have flexible IR lighting settings. Competent software configuration allows you to reduce the visibility of glow without physical modification of the device. Often the problem is solved by changing the threshold of inclusion or the power of radiation.
In the camera menu, you should find the section responsible for Day/Night regimes. Here you can adjust the dependence of the lighting power on the level of illumination. If the switching threshold is too high, the camera will go into night mode when there is street lighting, making red lights visible where they are not needed.
Menu -> Camera -> Display Settings -> Night Mode -> IR Brightness: LowIt is also worth paying attention to the function. Smart IR Or adaptive IR lighting. This technology automatically adjusts the intensity of the glow depending on the distance to the object, preventing illumination of closely spaced objects and reducing the overall glow in the frame. This makes the camera less visible to the observer.
⚠️ Note: When reducing the power of IR illumination software methods, make sure that in the observation area there are no other sources of IR radiation that can interfer with the light sensor.
Selection of equipment with invisible spectrum
If masking existing equipment does not yield the desired results, the most rational solution is to replace the cameras with models originally designed for covert surveillance. The market offers a wide range of devices, where the issue of visibility of glow is solved at the level of the construction.
Cameras with 940nm diodes, often referred to as "Black IRs," have no visible glow at all. However, as mentioned earlier, they are less effective. For longer distances, it is better to choose models with hybrid backlighting, where part of the diodes works in the visible range for a colored night, and part in the hidden.
- 🔍 Look for models labeled "Invisible IR" or "Zero Light."
- 📡 Pay attention to cameras with external IR spotlights, which can be masked separately.
- 🏗️ Consider the options for dome chambers with a darkened dome hiding the insides.
When choosing a new technique, it is important to pay attention to the angle of lighting dissipation. It should correspond to the angle of view of the lens. If the angle is too wide, the light will go to the sides and may be noticed. If it is too narrow, there will be a “tunnel” effect in the center of the frame. The right ratio of parameters is the key to invisibility.
Common mistakes when trying to hide the light
When trying to make the camera invisible, users often make mistakes that negate the effectiveness of the security system. The most common of these is the use of opaque materials that block both visible and non-transparent materials. infrared. The camera will go blind at night, recording a black screen.
Another mistake is the incorrect installation of external filters. If the filter is too far from the lens or diodes, it can create its own glare or reflections that will be visible on the recording. In addition, cheap materials can burn out or become cloudy over time, changing their optical properties.
And we must not forget about heat-radiation. Powerful IR spotlights are heated, and this heat can be noticeable to thermal imagers or even felt by the hand, giving away the location of the hidden camera. Thermal insulation in this case will not help, as it will block the useful radiation.
The main mistake is an attempt to seal the diodes with ordinary tape or black tape. This is guaranteed to disable the camera or make night photography impossible.
FAQ: Frequently Asked Questions
Can the red glow be completely removed from a normal 850 nm camera?
It is impossible to completely remove the glow without replacing diodes or installing a high-quality narrowband filter. The 850 nm filter will significantly reduce visibility, but a faint glow at point-blank range may remain. For 100% invisibility, 940 nm diodes are needed.
Does IR lighting affect the quality of color photography during the day?
No, it doesn't matter if the Day/Night switching mechanism is in operation. The day before the matrix lowers the IR filter (Cut-filter), which blocks infrared radiation, ensuring correct color reproduction. Problems only arise if the filter is jammed.
Is it safe to look at the lens of a working IR camera?
The radiation power of home security cameras is safe for the human eye with a short-term look. However, prolonged examination of the powerful IR spotlights included in the focus is not recommended, since infrared radiation can heat the tissues of the eye without causing a reflex blink.
Why does the camera see the remote control but not illuminate the object at night?
The camera matrix is sensitive to the IR spectrum, so it sees the remote diode. If the camera does not illuminate the object, the light sensor may be faulty, the LEDs themselves have burned or there is no power on the IR line, although the camera itself is working.