Talk:Infrared

General Comment

The definition of infrared in the opening paragraphs is inconsistent with the text. Authoritative sources (e.g. the McGraw-Hill Dictionary of Scientific and Technical Terms and the IEEE standard dictionary) define IR as extending down (in frequency) to 1mm or 1000 micrometers.

In terms of overall organization of the article, it would be better to either break some of the subtopics out into their own articles, or at least organize the materials so that it is a bit clearer that the various alternative categorizations of the IR spectrum are not different definitions for IR, but application-specific designations of bands within the broader IR spectrum.

(An aside, the last comment regarding the orders of magnitude question under "How does this make sense?" below, has it right.) —Preceding unsigned comment added by Neolute (talk • contribs) 15:34, 7 May 2009 (UTC)

Wavelength of Humans wrong?

The wavelength of 12 µm in the sentence "Humans at normal body temperature radiate chiefly at wavelengths around 12μm (micrometers), as shown by Wien's displacement law." is wrong!
Reasoning:
1. The Wien's displacement law article reads "Mammals at roughly 300 K emit peak radiation at 3 thousand μm K / 300 K = 10 μm".
2. My own calculations give at 37°C = 310,15 K give 9,34 µm.
Or did I forget something????
Michilans (talk) 15:40, 5 July 2010 (UTC)

Miscellaneous

"IF your computer monitor is warm, the following patch should be coloured infrared"

I like this joke a lot :-D. But technically, all objects above absolute zero radiate infrared, right?

I imagine if something gets cold enough its black body spectrum will have very little infrared in it, with the peak dropping down into the frequencies below infrared. There will still be infrared emission, but I'm not sure if the swatch could be termed to be colored infrared at that point. Maybe it would be colored microwave.

considering that no one can "see" infrared, it seems weird to say that it is colored as such. if the combination of colors creates other colors, then the square can't be "colored" infrared because it would then be a combination. if you say that it just emits or reflects infrared, then the color is still meaningless, because any visible color could do that if it contains IR reflective qualities. and, black would both emit and absorb IR since it absorbs, and it gets hot.

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Who wrote that about sunburn? are you sure? "Although relatively harmless, overexposure to IR can cause damage to cells and is the cause of sunburn (despite ultraviolet commonly being thought of as the culprit.)"

Scientific American seems to diagree: http://www.sciam.com/askexpert/medicine/medicine57/ --rmhermen

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How does the infrared in remote controls work? How does our sensation of radiated heat work? Does our skin sense infra-red, or does it heat up because of it and we then sense the heat (are the two different?) -- Tarquin 16:47 7 Jun 2003 (UTC)

I put in a few sentences about remote controls. As for skin, it senses heat, not radiation directly. There is a difference. Direct radiation sensing, as happens in the eye, is a photochemical process caused by photons colliding with light-sensitive (and, if you're a cat, IR-sensitive) molecules. These molecules are highly selective about what wavelength of photon they respond to, which is why we can see in colour. Heat receptors in the skin are different. It seems that nobody knows how they work, but they just sense temperature in the bulk of the skin. This temperature is mediated by mechanical vibrations of atoms, not by radiation. The skin receptors don't know if the heat got there by IR radiation, or by conduction from a hot object. By the way, some snakes can see infra-red, too, but they do it in a different way from mammals with IR-sensitive eyes. Their IR sensors, called pits, are separate from their eyes. The pits detect IR by its heating effect on the skin inside the pit. They can work out which part of the pit is hottest, and therefore roughly where the hot object is. -- Heron

thanks! The above is probably enough to make a start on Thermoception. -- Tarquin 19:45 7 Jun 2003 (UTC)

I find it cool how the Military has grasped this technology to make infrared goggles. —Preceding unsigned comment added by 216.227.15.93 (talk) 12:57, 14 May 2010 (UTC)

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The page happens to be in 4 (possibly 5) different categories that mean the same thing. This wiki definitely needs to merge categories to lower their numbers.

Infrared as a color - physical significance?

Do you have any way to modify the human eye so that we can see infrared as a color?? This should be known by 2100.

Our retina's red-sensing cones are far more sensitive to long wavelengths. The green and blue cones aren't going to give much of a signal. See http://www.4colorvision.com/files/photopiceffic.htm . So, if we view some light which is well above 700nM wavelength ...and if that light is so bright that it does become visible, then it will appear to be deep red in color. This is different than with some digital cameras which "see" infrared as orange or even turquoise color. The three RGB (CYM?) filters on the camera CCD may pass differing amounts of NIR, and if the blue filter passes more NIR than the red filter, the camera will see NIR light as being bluish. --Wjbeaty 19:23, 28 May 2006 (UTC)

It should? omigosh I better get to work then! WTF?!--Deglr6328 16:31, 16 Aug 2004 (UTC)

http://www.amasci.com/amateur/irgoggl.html Yes, and for $10.00. --Alexander

Even for less, just take a IR-fluorescence card for €0.10.--BoP 07:44:59, 2005-09-09 (UTC)

One of the historical discoveries was that the IR radiation boundaries had no physical significance, but was arbitrarily placed due to physiology. Where should I place that in the article? History?--Rayc 03:03, 9 September 2005 (UTC)

Can you give me a hint which physical properties have "physical significance" in current setting of wavelength regions? Today IR is subdivided mainly by the detector range, the transmission windows in an optical fibre and the sources available. Think of Terahertz radiation, some years ago this region was just an uninteresting subportion of IR-or mm-waves. What is the "physical significance" you want to mention? --BoP 07:44:59, 2005-09-09 (UTC)

Applications

I think the article is good so far. One of the things I missed in it was Remote sensing. In a Remote Sensing grad class I took several years ago we focused on biomass and plant stress measurements from the Landsat program images, high Near-IR reflectance for healthy plants. A good discussion of this can be found in http://rst.gsfc.nasa.gov/Sect3/Sect3_1.html

Another simplistic sensing use I saw in a documentary was imaging polar ice to find polar bears, ice reflects IR and polar bears absorb IR (not sure of the band likely near-IR from the images shown). Boris58 22:54, 27 September 2006 (UTC)

How about gaming applications, for example the Wii? This is also creating interest in homebrew hacks on the wiimote such as Johnny Chung Lee's Wii projects Zlog (talk) 12:44, 20 January 2008 (UTC)

As well as gaming applications, some mobile phones also use infrared, although Bluetooth is used mainly. Wikiert (talk) 18:07, 23 October 2008 (UTC)

There is a less popular application that the use of infrared heat is utilized. The asphalt industry used infrared machines to heat asphalt in place to repair and decorate areas. This is a industry that is becoming more popular by the day because of its respect to "green". This application of infrared technology has been in use since the 1970's. --Colinkeinath (talk) 21:09, 28 October 2009 (UTC)

Fahrenheit and Celsius scales

The image only has a Fahrenheit scale. Does anybody know how to add a Celsius scale to it? Bobblewik  (talk) 12:16, 10 Oct 2004 (UTC)

Done. --Heron 09:37, 12 Nov 2004 (UTC)

what danger can infrared cause?

It's non-ionising, so the only danger is due to heating. In other words, if it's powerful enough, it will burn your skin. --Heron 09:08, 12 Nov 2004 (UTC)

This is only true in a certain range of pulse lengths and intensities. There are several effects involved at higher intensities (like these found in lasers), like multiphoton processes, plasma generation and such. But in the low intensity case the heating effect is the dominant. --BoP 11:44, 2 Jan 2005 (UTC)

Besides the heating also electrical effects might influence particles at the resonant frequencies, this is where the particle has about the size of the radiation. Which is neglible for humans in the range below 2mm radiation. However cm long waves have shown that they can affect the hair of certain animals... --BoP 07:44:59, 2005-09-09 (UTC)

Related to the dangers of IR, in the "Different Regions in the Infrared" section, there is a mention that the 1530-1560 nm range is mainly used for long-range telecommunications. I've heard that this range is considered the "eye-safe" range. See here for a definition of "eye-safe". In general, I think the information in the previous link and this one from the same website explain some useful but simple ideas that could be incorporated into the article (if not already) such as why near-infrared light is able to permanently damage eyes, and 1.4+ micron light doesn't. This sort of gives context to why you shouldn't ever point a "laser" at someone's eyes. Or maybe just add a reference somewhere to the wiki article for laser safety, although ideally I think it should be the other way around. Kzero22 (talk) 19:19, 7 July 2010 (UTC)

15 micron band saturation and the greenhouse gas effect

I am doing some research on the question of the carbon dioxide greenhouse effect. Specifically, some critics of Global Warming claim that the 15 micron band is "optically saturated" for CO2 in the atmosphere. Further increases in CO2 will not have the expected effect, they argue, since the band cannot absorb anymore. There just ain't more 15 micron IR left to absorb. We would appreciate any info you could provide on this question. Specifically, how does the IPCC model IR saturation in the 15 micron band for the climate change predictions?

The center of the 15 micron band is saturated, but increasing CO2 concentration extends the unsaturated wings of the band, thus absorbing more IR radiation with increasing CO2 concentration. [1] treats this in some detail. The author there states that you can *still* increase the greenhouse effect by adding CO2 to the atmosphere if the CO2 level is 10 000 times higher than our CO2 level (3 atmospheres). Wikisteff (talk) 22:38, 12 November 2009 (UTC)

IR is not "Heat radiation"

The article and discussion here seems to reflect a common misconception about IR that I'd like to clear up. Basically, IR does not equal heat, "heat radiation", etc. Warm/hot objects radiate many wavelengths of electromagnetic radiation ("light"), INCLUDING infrared. Have you ever seen something extremely hot glow red? Or get hotter and glow orange, then yellow, then white? Same phenomenon.It glows IR first, you just can't see it. As for transmission of heat via IR, well yeah. Absorption of any wavelength of "light" warms things, INCLUDING infrared. Um, that's all. Thanks.

• EDIT*

After adding this comment, I went to clarify the article, and realized that this misconception /wasn't/ reflected in it after all. But in that case, what prompted me to post this and "fix" it? Twilight zone...

The article could be less wishy-washy if it clearly states that infrared "heat radiation" idea is simply wrong. After all, a snowbank puts out mostly microwave for its blackbody spectrum. And a 1000mW laser pointer can burn holes in objects. The IR/heat connection is a widespread misconception that's mostly supported by children's science books. But since we were all children at the start, even some physicists end up believing that IR is "heat radiation." One person who has written about this misconception is the physicist Dr. Chris Bohren, but I don't think his article is online anywhere. See his book on popular science, "Clouds in a glass of beer." --Wjbeaty 19:15, 28 May 2006 (UTC)

There still seems to be something missing in the article on the "heat" topic, it states that "IR light from the sun only accounts for 50% of the heating of the Earth, the rest is caused by visible light." Doesn't some of the heat on the earth come from other forms of electromagnetic radiation from the sun other than visible light? Or is the absorbtion rate for other non-visible electromagnetic waves that the sun produce just too low to count? This should be clarified, since the article also stated that "Light or electromagnetic waves of any frequency will heat surfaces which absorb it." --Tetrakatus 27 June 2006

Other heat-adding or heat-cooling mechanisms include:

* radioactive decay (adds heat);

* electromagnetic energy (adds heat);

* volcanic activity (chills surface, heats atmosphere)[1];

* solar wind (adds insignificantly)[2];

* lunar tidal heating (may influence additional volcanic activity)[3]; and

* greenhouse gases (traps heat).

[1] A. Robock, Volcanic Eruptions and Climate (2000)

[2] B. E. Wood, Astrospheres and Solar-like Stellar Winds (2004)

[3] J. G. Williams et. al, Lunar Power Dissipated by Tides and Core-Mantle Interaction (2000)

Hope that helps.

--User:Thangalin 23 September 2006

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Excuse me, I think this sentence in the Apps->Night-vision paragraph is a bit screwed up, could some native speaker take a look at it...? (you can delete this post afterwards) [bkil] 17:12, 11 July 2005 (UTC)

Smoke is more transparent to infrared than to visible light, so fire fighters use infrared imaging equipment when working in smoke-filled areas because it does not interfere with other devices in adjoining rooms - this is especially important in areas of high population density (IR does not penetrate walls).

I believe that a partial sentence describing indoor infrared comms got nixed with one on infrared firefighting equipment. Fixed it. Jaraalbe 20:27, 11 July 2005 (UTC)

Yup, just as I suspected! ;) Tx for your edit! :) 62.201.113.195 21:34, 11 July 2005 (UTC)

Didn't a Canadian, P. M. S. Blackett (poor guy, with those initials!) do research on infrared in WW2? --squadfifteen

Lower boundary of IR

I've tweaked the article a bit, since there seems to be no strong definition I can find of the exact boundary between visible and IR (I've seen 700nm, 750 nm, 760 nm, 780nm, and 800nm listed in various references and standards.) I've also added a paragraph addressing the issue. --Bob Mellish 18:10, 15 December 2005 (UTC)

Authors who give various IR boundaries just show that they don't understand how retinas behave. Since human retinas have no sharp frequency cutoff, therefore there can be no sharp boundary between IR and visible red light. Here's a good article on retinal response: http://www.4colorvision.com/files/photopiceffic.htm

On the other hand, for almost all practical purposes, 700nM is the boundary between IR and visible light. Our retinas are about 10,000 times less sensitive at 700nM than at the peak at 550nM (the green frequencies.) For scenes illuminated with broadband white light sources, the wavelengths above 700nM have far less than 1% contribution to visible red colors, and are essentially invisible. However, if the intensity of a 700nM narrowband source is cranked up by 10,000 times, it becomes just as visible as green light. Similar things are true of ALL near-infrared wavelengths: to easily see 750nM, turn up the brightness by about 200,000X. To easily see 800nM, turn up the brightness by about 10^7. The lower boundary of IR wavelenghts depends on the brightness and frequency distribution of the light source used as illumination. --Wjbeaty 19:15, 28 May 2006 (UTC)

One important note is that the visual system is stimulated by sources as a power law (see Stevens' power law for reference) with a coefficient between 0.33 and 0.5, depending on the source. That means that being 10 000 times less sensitive in photometric terms corresponds to between 20 and 100 times less sensitive in perceptual terms, which is not an insignificant difference. If one were looking at a monochromatic source in a dark room at 710 nm, one's eyes would certainly adapt to be able to see it as a dim red. You can easily test this by turning on an element on your stove to medium at night, if you have a dark kitchen. Not that I disagree with Wjbeaty, who seems to have it right. However, the lower cutoff adopted for IR matters a lot for the power contained in the infrared. Using 750 nm, the irradiance at the Earth's surface is 32 W/m² in UV, 503 W/m² in the visible, and 468 W/m² in IR. Using 700 nm as a cutoff, the irradiance at the surface is 32 W/m² in UV, 445 W/m² in the visible, and 527 W/m² in the IR. Wikisteff (talk) 22:45, 12 November 2009 (UTC)

Could it be that increasing the intensity is not making the the longer wavelengths more visible but the "red" that is perceived is the result of the natural harmonics present that are at unperceptible levels for lower intensities?Carywt64 (talk) 12:29, 13 October 2009 (UTC)

To Carywt64, received light has essentially no higher harmonics at normally-encountered intensities, as the energy densities required for nonlinear optical effects in most materials can only be found in very high-powered lasers. So it's a real effect of wavelength. Wikisteff (talk) 22:45, 12 November 2009 (UTC)

Ahooo

Riiight, it's a wolf. This dangerous animal can be seen at http://coolcosmos.ipac.caltech.edu/image_galleries/ir_zoo/dog.html --Femto 14:20, 6 April 2006 (UTC)

Cellphones

Can someone add the use of infrared on cellphones. --MarioV 01:05, 1 August 2006 (UTC)

Ice cubes emitting microwave?

and ice cubes emit mostly microwaves...

It doesn't match. If microwaves start at 1 mm, according to Wien's displacement law the top wavelength should be about 2.9 K! Sure water is frozen at that temperature, but it is not what I mean with just ice cube. --Pinzo 19:49, 4 October 2006 (UTC)

CADPAT

The Canadian Army uses a type of camouflage called CADPAT that reportedly reduces or conceals IR. Think this should be included?

--JodoYodo

Different regions in the infrared

This section is lacking in any references and so it is unclear who is using the listed "schemes" or how they are applicable. I have no idea how this information was derived. It could be complete rubbish for all I know. Should the first two "schemes" be scrapped? Thanks. — RJH (talk) 18:55, 3 April 2007 (UTC)

Citations

Why are there so many sections in this article that are missing citation? --the_hoodie 17:21, 23 May 2007 (UTC)

The fact "Humans at normal body temperature radiate chiefly at wavelengths around 10μm" cites a page that does not contain that information

That was boned by this anon IP edit in Dec. 2008. I'll take it out. Dicklyon (talk) 15:17, 26 October 2009 (UTC)

Missiles

homing on to the IR signature of the target aircraft, typically the jet engine exhaust plume.

My understanding was this is NOT true; IR missiles home in on the hot metal of the tailpipe, not on the gases themselves which are too diffuse to track. But then this is old information and I know IR seeker heads have changed since then. The sources I can Google talk about both hot metal and exhaust plumes, but they're not all that great ( a lot are corporations with a product to sell ) so I would hope somebody has a good book they can check.

Eleland 20:07, 25 June 2007 (UTC)

therapeutic uses

This documents a new one, but there are other, better known therapeutic uses such as for cramps etc. --Espoo 18:08, 27 June 2007 (UTC)

"FIR is also gaining popularity as a safe method of natural health care & physiotherapy. Far infrared thermometric therapy garments use thermal technology to provide compressive support and healing warmth to assist symptom control for arthritis, injury & pain."

The above reads like it came straight from an info-mmercial. Before you know it someone will add some BS about the "benefits" of embedded amethyst crystals in your clothes, or something equally asinine. The marketing jargon should be dropped and simply something to the effect of "insulating garments and wraps can increase blood flow to the extremities, perhaps relieving pain and accelerating healing." Ideally, a legit source should be provided to justify the claim. Also, "compressive support" is completely unrelated to an insulating clothing item, which may or may not be compressive. 143.215.217.47 (talk) 18:37, 13 April 2010 (UTC)

IR Blaster / IR Blast Diode

Should something be added about an IR Blaster or IR Blast Diode used to actually create the IR signal?166.20.114.10 15:49, 6 July 2007 (UTC)

Night Vision

Added a couple of references resolving some year old tags. Rewrote the Night Vision section as it was confusing night vision which deals with infrared light and thermal imaging which deals with infrared radiation. Arcos9000 04:36, 13 August 2007 (UTC)

Thermography copyright violation

In November 2006, user 70.91.43.253 replaced the entire Thermography section of the article with text copied from http://www.infraspection.com/FAQ.html. (Here's a link from archive.org, showing that they had the text before it was added to Wikipedia.) I've reverted the section to the previous version.  --mconst 01:16, 2 November 2007 (UTC)

Wavenumbers

Can we add wavenumbers (cm-1) into this article. They are an extremely common way of measuring infrared frequencies

what is the history of infrared rays? KALIY Smith —Preceding unsigned comment added by 75.49.37.47 (talk) 00:48, 20 March 2008 (UTC)

Heat - Infrared - The resulting frequencies from external stimuli

I have been wondering for years: There are apperantly infinate frequencies for an object to be stimulated with/by. However, I wonder if the heat generated, due to the stimulation, is part of the reaction of the object limited to the infrared range? David Colley 75.0.13.223 (talk) 16:54, 22 March 2008 (UTC)

No.

How does this make sense?

Towards the beginning of the article it says: "Infrared radiation has wavelengths between about 750 nm and 1 mm, spanning five orders of magnitude." How is 750-1000 five orders of magnitude? Isn't this only 1/4 of an order? Or is there some base other than 10 which is being referenced? Anyone? 65.183.135.231 (talk) 19:03, 19 May 2008 (UTC)

750 nm is 0.75 μm and 1 mm is 1000 μm. Seems like 3 orders of magnitude to me. Thunderbird2 (talk) 19:06, 19 May 2008 (UTC)

Doh!65.183.135.231 (talk) 19:20, 19 May 2008 (UTC)

History cruft

The history cruft was added by a drive-by anon here; since we don't have anyone we can ask about sources, I recommend we just flush the unsourced stuff. OK? Dicklyon (talk) 19:02, 18 December 2008 (UTC)

Candela for sunlight

It is strange to mention the candela value of bright sunlight in relation to how much of the sun's energy that reaches earth's surface is IR. Candela is a unit weighted for the perception of humans, so all IR light will have an irradiance of 0 candela, no matter how bright. "Bright sunlight provides luminance of approximately 100,000 candela per square meter at the Earth's surface." I would instead use the total radiant flux of the sun across all wavelengths.

122.161.6.100 (talk) 11:05, 23 August 2009 (UTC)

Hey, I just fixed the candela and lumens per Watt to be something more useful, along the lines of your initial comment. Wikisteff (talk) 22:50, 12 November 2009 (UTC)

Article

Is the subject of this article supposed to be infrared, or infrared radiation? "Infrared" can imply something broader, such as interactions with matter, and "IR radiation" is more specific. Which is it? Tranh Nguyen (talk) 04:54, 15 October 2009 (UTC)

It appears to be infrared radiation, broadly construed, including applications. Dicklyon (talk) 04:56, 15 October 2009 (UTC)

So shouldn't the article be titled "Infrared Radiation"? The ambiguous "Infrared" as a title seems odd, and implies a wider discussion of heat, etc. Tranh Nguyen (talk) 05:02, 15 October 2009 (UTC)

I think the current title is fine. If there's some other infrared topic that needs to be distinguished, show us and we can consider what to do. Dicklyon (talk) 05:03, 15 October 2009 (UTC)

Be sure to cite your sources when you add information, so we can verify it or express it better to agree with the source. Dicklyon (talk) 06:49, 15 October 2009 (UTC)

Frequency values.

Infrared radiation is right at the intersection of two different schools of measurement: The first being the measurement of visible light (commonly measured by length), the second being the measurement of radio frequencies (commonly measured by frequency).

As a result, it's important to list the ranges of infrared using both wavelength and frequency. I've added frequency values in the lead section of the article. InternetMeme (talk) 11:36, 26 November 2009 (UTC)

Solar Irradiance

In Raymond S Bradley's book Paleoclimatology the figure of 342 wm^-2 but it is not broken down. The figure given in the article is 1kwm^-2 and is broken down. Can someone explain the difference between these two figures? Wilmot1 (talk) —Preceding undated comment added 10:16, 10 December 2009 (UTC).

Heat Seeking Telescope

The Times:-Dominic Dyer, chairman of CWI. “These animals are being wiped out by poachers who are increasingly well equipped with automatic weapons, GPS satellites, night-vision kit and heat-seeking telescopes to spot animals at night."

Do these heat seeking telescopes home in on the animals and automatically control the positioning of the telescopes to track them? Isn't this how the Spitzer Space Telescope works? Kwenchin (talk) 01:53, 21 March 2010 (UTC)