Q: What is "Split-Glass" design and why is it important for night vision? A: When the front lens cover uses two pieces of glass separated by a metal ring to prevent LED light from reflecting back into the lens and causing a foggy effect.
IR back reflection, also called “light scatter”, is evident in the above captured image from a single plate bullet camera. In the lower right corner there is a foggy “port hole” effect along with visual artifacts which appear to be swirling around the van in the upper right corner. During daylight hours the camera’s picture looks normal and is of reasonable quality.
The above diagram shows a cut-out, side view of the typical bullet camera design that uses a single plate of glass to cover the lens and LED assembly. The drawing illustrates how IR light can bounce inside the glass plate an eventually into the outer edges of the lens. One result of this light can cause a halo effect which makes the outer perimeter of the picture look foggy. Problems can occur with a brand new camera and get worse when small amounts of dirt or grime build up on the glass. The slightest amount of dirt or water residue can increase the back reflection properties of the glass.
Pictured above is an example of a camera using a conventional single glass face plate with a rubber bushing to surrounding the board lens. Despite having 12 more LEDs than our 1R-0070-35IR, it had an inferior night vision range and suffered from a foggy halo effect within an hour of sunset.
Split Glass Design Makes Back Reflection Impossible. Shown above is the split-glass design that is employed by all our outdoor bullet and vandal proof dome cameras. Unlike with the single glass design, it is impossible for LED light to travel into the camera lense through the front glass cover plates because they are physically separated by a metal shield.
Above is our 1R-0070-35IR bullet camera with the front cap removed to better show the split glass design. Notice that the inner and outer glass pieces are physically separated by a metal light shield which completely blocks all LED light from directly reflecting back into the lens.