Why Thermal Imaging Devices Don’t See Through Glass and Other Common Questions

Thermal imaging devices are powerful tools for detecting heat signatures, whether for hunting, wildlife observation, home security, or professional use. However, they come with unique limitations and quirks that can sometimes surprise users. One of the most common questions we hear is: “Why can’t thermal imaging see through glass?” This article addresses that question and covers several other FAQs about thermal imaging technology.

1. How Thermal Imaging Works: Thermal devices detect infrared light emitted by warm objects and convert it into a visible image. When this infrared light hits a surface like glass, the glass reflects most of it rather than allowing it to pass through.

• What You See: Because glass reflects infrared radiation, a thermal device aimed at a window will typically capture a “mirror” image of what’s in front of it. This means you’ll see the heat signature of objects behind you or on the same side of the glass as the thermal device—not what’s on the other side of the glass.

2. Material Composition Matters

• Glass is designed to allow visible light to pass through, but it blocks most infrared radiation. Materials like Silicon, Germanium, or Chalcogenide glass, on the other hand, are more transparent to infrared light and are sometimes used in specialized lenses for thermal devices.

• Special Thermal Lenses: High-quality thermal imaging devices like those from Armasight use infrared-transparent materials like “Germanium” for their lenses to capture accurate heat signatures. However, these lenses are made from materials different from everyday window glass.

Common Questions About Thermal Imaging Technology

Thermal imaging is a unique and complex technology, and users often have questions about what it can and can’t do. Here are answers to some of the most frequently asked questions to help you get the most out of your thermal device.

Can Thermal Imaging Work Through Fog, Rain, or Snow?

Thermal imaging devices can detect heat signatures in various weather conditions, but fog, rain, and snow can affect their performance.

• Fog: Fog can reduce the clarity of a thermal image since it cools and diffuses the infrared radiation emitted by objects. High-end thermal devices with sensitive detectors can still detect heat signatures through light fog but may experience a loss in range and detail.

• Rain and Snow: Heavy rain and snow can absorb and scatter infrared radiation, making it more challenging for thermal devices to produce a clear image. While thermal imaging is more effective in these conditions than visible-light cameras, extreme weather can still impact image quality.

Can Thermal Imaging Detect Through Walls?

No, thermal imaging cannot “see” through walls in the traditional sense. Here’s why:

• Surface Temperature Detection: When you point a thermal camera at a wall, it detects the surface temperature of the wall itself, not what’s behind it. Walls, particularly those made of materials like concrete or brick, block infrared radiation from the other side.

• Exceptions in Certain Cases: If an object on the other side of a wall generates enough heat, some of that heat may transfer to the wall’s surface. For example, a large hot object or fire might warm up the wall enough for a thermal device to detect the heat difference on the wall’s surface. However, this is limited to situations where the heat source is significant and close enough to affect the wall’s exterior.

How Far Can a Thermal Device “See”?

The effective range of a thermal imaging device depends on several factors:

• Device Resolution and Sensitivity: High-resolution, high-sensitivity devices (like those from Armasight) can detect heat signatures from greater distances and produce clearer images. For example, a thermal scope with a 640x480 resolution can detect a human-sized heat signature from several hundred yards away.

• Weather Conditions: Temperature and environmental conditions impact range. Cold, clear nights tend to offer the best thermal imaging conditions, as heat signatures stand out more against the cooler surroundings.

• Size of the Heat Source: Larger heat sources, such as a car or a building, can be detected from farther away than smaller ones, like a small animal or a distant human figure.

Can Animals or Humans “Hide” from Thermal Imaging?

Thermal imaging is highly effective for detecting heat signatures, but certain techniques can limit visibility:

• Barriers that Block Infrared Radiation: Materials like thick clothing, walls, or glass can obscure or reduce the visibility of a heat signature. For example, hiding behind a wall or inside a vehicle can make it challenging for a thermal device to detect an individual.

• Thermal Camouflage: Special thermal blankets or suits that reflect or absorb infrared radiation can obscure body heat, making it harder for a thermal device to detect someone. However, this level of thermal concealment is typically used in specialized settings rather than general use.

• Environmental Blending: In cold environments, individuals or animals that remain close to objects with similar temperatures (like large rocks or cool ground) may blend into the background. High-quality thermal devices, like those from Armasight, are designed to maximize sensitivity and contrast, helping to minimize this effect.

Can You Use Thermal Imaging in Daylight?

Yes, thermal imaging devices work equally well in daylight as they do at night. Unlike night vision, which relies on light amplification and is therefore less effective during the day, thermal imaging detects infrared radiation, which is unaffected by visible light levels.

• Advantages of Daytime Use: Thermal imaging can be helpful during daylight for spotting wildlife camouflaged in foliage, detecting warm machinery or infrastructure, and identifying heat leaks or insulation issues in buildings.

• Avoiding Overheating: Be mindful of direct sunlight on the device, as extreme heat can affect performance. High-quality Armasight devices are built to withstand typical field conditions, but storing them in direct sunlight for long periods isn’t recommended.

Key Takeaways for Thermal Imaging Device Use

Thermal imaging is a powerful and versatile tool, but like any technology, it has its limitations. Here’s a summary of the main points to keep in mind:

• Glass and Infrared Reflection: Thermal imaging can’t see through glass due to reflection, so aim directly at objects rather than through windows or windshields.

• Weather Impacts on Performance: Fog, rain, and snow can affect thermal imaging quality, though it generally performs better than visible-light cameras in adverse weather.

• Limited Detection through Solid Barriers: Thermal imaging detects surface temperature, meaning it can’t “see” through walls, but high heat sources may affect wall surfaces.

• Thermal Imaging in Daylight: Daytime conditions won’t impact thermal imaging capabilities, allowing effective use 24/7.

Armasight: Precision Thermal Optics Built to Last

Armasight’s thermal imaging devices are built with precision materials and cutting-edge technology to deliver clear and accurate heat detection, even in challenging environments. From reliable construction to advanced sensitivity, Armasight’s products are designed to handle the demands of both professional and recreational use.

Our thermal imaging devices provide hunters, observers, and security personnel with the tools they need to stay effective and undetected in any environment. With Armasight, you’re equipped with technology that offers maximum performance and a deep understanding of how to use it to your advantage.