Prevent / reduce IR reflections on dome cameras with built

Prevent / reduce IR reflections on dome cameras with built
Prevent / reduce IR reflections on dome
cameras with built-in IR
November 24th, 2015
Introduction
LILIN dome cameras with built-in IR illuminator enable video surveillance at night or in
dark environments. The IR illuminator provides discreet and covert illumination for
network video while minimizing light pollution. However, IR-light reflected by close
objects can significantly deter image quality at night. The reflections may cause a cloudy
effect in the image or mirroring effects in the bubble. In some cases you may even see
the camera lens mirrored in the bubble. This is usually caused by either:
- IR-Reflection from nearby objects
- Reflections from external light sources
- Water droplets on the outside of the bubble
- Dirt and dust
Below we have listed a few considerations that should be taken into account to avoid
these potential problems and achieve the best possible results.
1. IR-Reflections on nearby objects
Walls, eaves, ceilings and other objects may reflect IR light back into the camera. The
strength of this effect depends on the proximity and surface of the object. As a rule of
thumb, light and glossy surfaces, metal and glass will reflect more light than dark, matt
objects.
Avoid direct reflections from nearby objects. The IR beam should not be directed
towards near walls or ceilings, windows and other objects with high reflectivity. The
camera’s angle of illumination might be wider compared to the angle of view so you
should not rely on the camera image to determine if an object is in the path of the IR
beam. Highly reflective objects could be covered or painted to reduce reflections.
External light (for example another camera or white light lamp) pointing towards the
camera might lead to reflections in the bubble.
2. Lens orientation
When installing the camera on wall or ceiling, the lens should be tilted as little as
suitable for the installation to avoid reflections from the nearby surfaces. The antireflective rubber ring around the lens should not be removed as it prevents light
interference. It is important that the rubber touches the bubble.
In this image the lens is positioned to low in the housing. No.1 half the LED’s are hidden
behind the housing. No.2 the anti-reflective rubber ring is also positioned beneath the
housing meaning light can leak in.
This is the result you get if
you position the lens as
above
This image demonstrates an improved lens position. No.1 the LED’s are not hidden.
No.2 the anti-reflective rubber ring is in full view, meaning no light can leak through.
Finally the wider angle that you set the lens the more susceptible the video image to
showing IR leak/reflection
.
3. Dust, dirt, rain, finger prints, snow and ice
Even small water droplets, dust, and other objects such as spider webs on the bubble
will deteriorate image quality substantially by reflecting IR light. If possible, the camera
should be mounted in a place where it is less exposed to the weather. The use of a wall
bracket may reduce (but not illuminate) the domes exposure to the above.
The camera bubble should be regularly cleaned to remove dirt and dust. We recommend
to use a mild soap detergent, water and a soft microfiber cloth to avoid scratches on the
camera. Dust on the camera could be removed with compressed air.
In some situation where water droplets are a common issue it may help to regularly
apply a water repellent spray on the outside of bubble such as those used for the visors
of motorcycle helmets.
This image was taken with a
clean dome cove
A thumb print was then
applied to dome cover
This image shows the
immediate effect of a single
thumb print
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