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Web Cams & IR Response

Does anyone know if Web cameras (PC cameras, whatever you want to call them) based on CCD technology have any kind of infra-red response, i.e. they will produce an image in complete darkness if lit with infra-red?

Since most black & white security cameras use CCD technology and do work (to varying degrees) with IR illumination i'm wondering if Web cam's would be the same.
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paulburns
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paulburns
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RoadWarriorCommented:
They usually have some response to the near infra red, this can be seen if you have them capture a sequence of pics while pointing a remote control from a tv etc at them, with a button pressed. Usually the monochrome ones are more sensitive. The thing that usually costs the bucks in this type of application is the source of illumination, especially if you need it not to be obvious to the naked eye. The cooler a CCD device is, the better it picks up infra red, so playing about with peltier coolers might be in order here, take a look at some CCD astronomy pages online and you will get some tips for this sort of thing. Bear in mind that fixed focus cameras will give a very blurry image used in infra red light since the focal length must necessarily be longer because infra red light has longer wavelengths, so get hold of or make a method of focussing.

regards,

Road Warrior
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paulburnsAuthor Commented:
Thanks for the info. I didn't know that cooling a CCD gives better IR response so will have to look into that. I was going to make up a light source using IR LED's, don't know how effective it will be though.

Anyway, i'd like to leave this open for a few days, but if there are no more comments you can have the points.

Thanks again.
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RoadWarriorCommented:
LED's would be okay if you were trying to light a small space, a very small space, say a nesting box for birds, for nature photography purposes, then a dozen or so could give you enough light to get a picture, but if you wanted a range of feet instead of inches, then you'll need some powerful spotlamps with IR filters. Think of  lighting a room with regular LED's, not practical huh? You need the IR equivalent of a couple of auto headlights.

Semiconductors increase in resistivity when temperature lowers. Light or heat falling on a semiconductor decreases the resistivity, so to spot faint light differences, the base resistivity should be kept as high as possible, by keeping them cool.

Road Warrior

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paulburnsAuthor Commented:
>> Semiconductors increase in resistivity when temperature lowers. Light or heat falling on a semiconductor decreases the resistivity, so to spot faint light differences, the base resistivity should be kept as high as possible, by keeping them cool.


Are you sure about this? i always thought lowering temperature decreases resisitivity - think of superconductors.
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RoadWarriorCommented:
That's why semicomductors are unique. Basically, what happens is the means of conduction in a semiconductor is depandant upon the number of charge carriers available to convey the charge, charge carriers are electrons and holes, these are limited, there is not the abundance of a free electrons as in a metal, the electrons are more tightly bound to the atoms, so it requires input of energy to shake any loose. Heat or light energy will allow more electrons to escape from their atoms, overcoming the binding energy of the atom. So, when either heat or light is applied a semiconductor becomes more conductive. The conventional response of a conductor would apply when there is suffcient charge carriers free, but usually the energy required to make this amount free induces change of phase in the semiconductor, it also will have lost it's interesting properties, so no-one is really interested in doing this.

regards,

Road Warrior
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