Infrared Light filtered out by double pain window?

[LittleScoobyMaster 0]

Hey everyone.

 

Realizing a non-optimal situation whereby an infrared illuminator such as the one listed below must be placed inside a house and pointed out through a double-pain window to the back yard versus being mounted outdoors, can anyone tell me approximately how much infrared light would be filtered out of the illuminator by the standard double pain window?

 

I'm looking for a rough percentage based on an average clear double pain window. For instance, will 10% of the infrared be filtered out, or 20%, or 50%? thanks

 

note: I'm not concerned about bounce back of the infrared light into the camera lens because the cameras are located in different windows in different rooms pointing towards the area outside that will be lit up by the infrared light.

 

Illiminator:

http://www.bhphotovideo.com/c/product/1058345-REG/axton_16n28120_orion_m_120_deg_850nm_indoor_outdoor.html

[the toss 0]

It will depend on the type of glass (laminated , hardened , etc) but for standard window glass you will be getting around 90% attenuation.

[LittleScoobyMaster 0]

It will depend on the type of glass (laminated , hardened , etc) but for standard window glass you will be getting around 90% attenuation.

 

Thanks

 

I think of attenuation as a loss, so to clarify, are you saying that 90% of the infrared light would be filtered out of standard double pain clear glass so that only 10% of the infrared light will make it out of the window?

 

Or do you mean that 90% of the light would make it out of the window and 10% of the total amount of infrared light would be lost?

[survtech 0]

A lot depends on the design of the windows. Low-E windows are designed to reflect IR back outside so a low-E window passes little IR. Standard glass passes a fairly large percentage of IR.

 

There are also two different types of low-E glass: one is designed for colder climates and actually passes IR to optimize solar heating during cold months. The other type is designed to reflect all IR back outside. It also depends on the exact wavelength of the IR. Low-E is not a perfect reflector of all wavelengths of IR light. It reflects more of the IR light the further it is away from visible light in wavelength. Since IR for cameras is very close in wavelength to visible light, even low-E glass will pass a fair percentage of it.

 

The three types of IR illumination are 715-730nm, which produces a red glow like a red traffic light, 815-850nm, used for semi-covert IR with a faintly red glow only just visible and 940-950nm, which is totally covert. The shorter the wavelength, the less it will be attenuated by the windows. Most IR illuminators use 815-850nm light.

 

So your answer is "It depends..."