Generally, most night vision devices do not work effectively behind standard glass. The reasons depend on the type of night vision technology being used.
Types of Night Vision and Glass Interaction
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Image Intensification (I²): These devices amplify existing ambient light (starlight, moonlight) and near-infrared (NIR) light.
- Standard glass can allow some ambient and NIR light to pass through. However, if the I² device uses an active infrared (IR) illuminator, the IR light will reflect off the glass surface back into the device, causing a "white-out" effect or severely obscuring the view.
- Even without an active illuminator, reflections from the internal optics of the device or ambient light from behind the user can reflect off the glass, degrading the image.
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Thermal Imaging: These devices detect differences in heat signatures (mid-wave infrared, MWIR, or long-wave infrared, LWIR).
- Standard window glass is largely opaque to the LWIR and MWIR frequencies that thermal imagers detect. Instead of seeing through the glass, the thermal imager will primarily see the temperature of the glass itself, or reflections of other heat sources off the glass surface.
- Specialized, expensive materials like Germanium, Sapphire, or Zinc Selenide are transparent to certain infrared wavelengths and are used for thermal camera lenses and windows, but these are not typical for building or vehicle glass.
In summary:
While you might get a very degraded image with an image intensification device through glass under specific, ideal conditions (no active IR illumination, minimal reflections, sufficient ambient light passing through), it's generally impractical.
Thermal imaging devices will almost universally not see through standard glass; they will see the temperature of the glass surface.
