Infrared Illumination / IR through glass

[DigiTan]

PART 1:
I'm setting up a security camera. It's got to work day or night and I'm trying figure out the best way to illuminate scene without a visible light source. I've seen commercial security cameras fitted with the near-IR diodes but it's hard to gauge for myself whether that would work at the range I need. Are they practical at--say--40 feet?

PART 2:
I'm trying to trigger the recording by either sound or motion through a window pane. If possible, I was to have the IR motion detector. Near-IR seems to pass the glass; no problem. Will long-IR from body heat pass at all?

 

[DigiTan]

Well, looks like I found PART 1. There's some places that sell IR Spotlights, which are pretty much IR versions of those high-powered spotlights you find in the sports/outdoors aisle. The version I'm getting runs at 1000nm, so it's completely discrete. I'm trying to find one for a reasonable price.

 

[Brian Hoskins]

Make sure your camera is sensitive to the same wavelength as the floodlight you buy (or as close to as you can).

Brian

 

[Hero999]

Will long-IR from body heat pass at all?

No, I don't think it will.

You could use a computer system connected to the camera to sense when the picture changes significantly and start the recording.

 

[Nigel Goodwin]

[DigiTan] Will long-IR from body heat pass at all?

No, I don't think it will.

You could use a computer system connected to the camera to sense when the picture changes significantly and start the recording.[/QUOTE]

Or just record 24 hours a day, which makes much more sense, and is far more reliable.

 

[Brian Hoskins]

The problem with recording 24 hours a day is there's no way you can review the recording for interesting events later. I use mine on motion detect which works in the same way Hero has described because then I can review a night's events on a daily basis. There's no way you can do the same thing with a 24 hour recording, so you have to rely on noticing when an interesting event has occured (like a scratch on your car for example) and then trawling through hours of recording in fast forward mode to try and catch it.

I think a mixture of the two options would be a good compromise. So the system records 24 hours but inserts markers when motion is detected. In that way you get the reliability of 24 hour recording (all events are captured) and the searchability of event recording. My system does not have that option unfortunately.

Brian

 

[jpanhalt]

Will long-IR from body heat pass at all?

No, I don't think it will.

So, why do we make such a fuss over thermal pane and similar windows to improve insulation and decrease heat loss? John

 

[Hero999]

That's a fair point.

But isn't more heat lost from windows by conduction rather than radiation?

Isn't this why double glazing is such an effective method of insulation.

 

[jpanhalt]

But isn't more heat lost from windows by conduction rather than radiation?

True, but not related to the question of whether window glass transmits (enough) IR for images.

From: https://en.wikipedia.org/wiki/Infrared_radiation

Near-infrared (NIR, IR-A DIN): 0.75-1.4 µm in wavelength, defined by the water absorption, and commonly used in fiber optic telecommunication because of low attenuation losses in the SiO2 glass (silica) medium. Image intensifiers are sensitive to this area of the spectrum. Examples include night vision devices such as night vision goggles.
Short-wavelength infrared (SWIR, IR-B DIN): 1.4-3 µm, water absorption increases significantly at 1,450 nm. The 1,530 to 1,560 nm range is the dominant spectral region for long-distance telecommunications

See: Attached transmission spectrum of soda lime glass (window glass, untreated).

The basic problem, as noted in the Wikipedia reference is absorption by water. Related substances, such as sapphire are better at transmission of IR and are used in heat-seeking missiles for that reason, but glass still a good proportion of transmits IR heat. John

 

[Boncuk]

Scanners use quartz glass for mimumum losses. May be you'll find an inop scanner and use that glass.