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I am planning to obtain near infrared light for a project. Instead of producing the infrared myself, I thought it might be easier to use something inexpensive and commercially available. That's why I am wondering if the white light of a flashlight or a lightbulb also emits significant amount of infrared light? If not, is there anything else I can use to obtain IR in an easy way?

I'm interested in 700-800nm, and I will be filtering out the rest of the light, so efficiency or rest of the spectrum do not matter.

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    $\begingroup$ Easiest thing to do would be to go to eBay and order a 10W 740nm (near IR) LED and a cosntant current driver for it $\endgroup$
    – user56903
    Feb 23, 2016 at 16:47
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    $\begingroup$ Be careful - they can potentially cause eye damage $\endgroup$
    – user56903
    Feb 23, 2016 at 17:00

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You can easily show that an incandescent lamp produces infra-red as follow but whether it will be enough for your purposes I do not know.

Try the following experiment.
Select a mains lamp probably in a table lamp which has not been turned on for some time ie it is cold.

With the lamp off feel the glass enevelope. It should feel cool.

Without actually touching the glass cup you hands around the lamp and get somebody to switch the lamp on for about 5 seconds.

With the lamp off feel the glass envelope.

The glass should feel cold and yet you got the sensation of heat when the bulb was on - that was the infra red radiation emitted from the bulb.

Perhaps this experiment or measuring the temperature rise above room temperature of a mercury of alcohol thermometer with a blackened bulb may help you decide if an ordonary light bulb is sufficient for your purposes?

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Such light sources can be closely modeled as blackbody sources. So, if you look up the spectrum of a blackbody source with temperature ~1000C you can get an idea for how much IR there is.

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Yes, an incandescent bulb certainly produces a significant amount of infrared radiation. Indeed, the spectral flux in wavelength of an incandescent bulb is actually greater in the 700-800 nm range than in the visible spectrum, as shown in this image.

In terms of where the consumed energy goes, incandescent bulbs are essentially primarily electric heaters, that secondarily have a side effect of producing visible light.

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  • $\begingroup$ Well, to be a nitpicker, all EM radiation leads to heating. It's just that we make use of the small percentage of visible-range photons that reach our eyeballs before being absorbed by something else in the room for vision as opposed to heating things :-) $\endgroup$ Feb 23, 2016 at 20:18

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