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Science

People Emit Visible Light 347

Posted by timothy
from the lots-of-girls-I-know-glow-visibly dept.
An Anonymous Reader writes "The human body literally glows, emitting a visible light in extremely small quantities at levels that rise and fall with the day, scientists now reveal. Japanese researchers have shown that the body emits visible light, 1,000 times less intense than the levels to which our naked eyes are sensitive. In fact, virtually all living creatures emit very weak light, which is thought to be a byproduct of biochemical reactions involving free radicals."
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People Emit Visible Light

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  • Establish in 2005 (Score:5, Informative)

    by eldavojohn (898314) * <eldavojohn@gmFREEBSDail.com minus bsd> on Thursday July 23, 2009 @03:13PM (#28798721) Journal
    I thought this was discovered and establish in 2005 by Mitsuo Hiramatsu, a scientist at the Central Research Laboratory at Hamamatsu Photonics [quantumbalancing.com]. The only new information I recognize is that it varies by time of day, not that people emit visible light. Did this new study find anything else out additionally or just make pretty pictures that show it?
  • by amRadioHed (463061) on Thursday July 23, 2009 @03:23PM (#28798879)

    From wikipedia [wikipedia.org]: "The visible spectrum is the portion of the electromagnetic spectrum that is visible to (can be detected by) the human eye. Electromagnetic radiation in this range of wavelengths is called visible light or simply light."

  • by Bemopolis (698691) on Thursday July 23, 2009 @03:24PM (#28798899)
    No. His argument, correct but incompletely stated, is that any macroscopic object with a temperature emits a blackbody(-ish) spectrum which, since it spans the entire range of EM radiation, emits some light in the visible portion of the spectrum.
  • by thisnamestoolong (1584383) on Thursday July 23, 2009 @03:24PM (#28798913)
    The terms are a bit confusing, but the term "visible" light has nothing to do with magnitude, it only refers to light with a particular wavelength, roughly 380 to 750 nm, which our retinas happen to be sensitive to. The term visible is not meant to differentiate visible light from invisible light, but rather to differentiate these waves from radio waves, infrared, ultraviolet, X rays, microwaves, and gamma rays. So yes, even if the light cannot be seen, if it is in that particular spectrum, it is visible light.
  • by Draque (1367509) on Thursday July 23, 2009 @03:25PM (#28798917)
    You're right that they need different energies. If you graph the energies of photons emitted due to heat radiation, they'll form your typical bell curve, with the peak of the bell curve representing and energy level corresponding with infra-red radiation. That having been said... a few standard deviations from the center, you'll see the (very rare) photons emitted that have energy levels corrosponding with visible light. This happens when enough energy concentrates (by random, highly unlikely chance) to create a photon with much higher energy than is typical for a radiating body. It's very, very unlikely for ay given photon, but photons are created very, very often, so it happens frequently, though not enough to create intense enough light to see.
  • by amicusNYCL (1538833) on Thursday July 23, 2009 @03:30PM (#28798995)

    Visible in this context doesn't mean perceptible, it's describing the wavelength, not the intensity. The light is very low intensity that has a wavelength within the visible spectrum.

  • by Eukariote (881204) on Thursday July 23, 2009 @03:30PM (#28799001)

    This isn't any kind of new or unpredicted phenomenon.

    It is definitely unpredicted by conventional theory. The visible part of the black-body radiation spectrum (which you seem to be referring to) for an object at human-body temperature is far less than 1/1000th of what is still visible. These emissions are therefore not thermal. And the is no other conventional theory that mandates such emissions.

  • Re:Biophotons (Score:1, Informative)

    by Anonymous Coward on Thursday July 23, 2009 @03:35PM (#28799057)

    It's just simple blackbody radiation. Anything with a temperature emits blackbody radiation, which is made up of photon that are mostly infrared. But the various photons have different frequencies, and some of those frequencies are in the visible spectrum.

  • by geekgirlandrea (1148779) <andrea+slashdot@persephoneslair.org> on Thursday July 23, 2009 @03:36PM (#28799073) Homepage
    See Planck's law [wikipedia.org]. The power density at a given wavelength is inversely proportional to an exponential function of the photon energy, for wavelengths short compared to the peak. For humans (37 celsius), the peak lies at about 9.3 microns. If this were thermal radiation from a blackbody spectrum, the exponent for the longest visible wavelengths would be about 66.3, corresponding to about 1.9 * 10^-20 W/m^2 of radiated power in the visible spectrum, assuming perfect emissivity. If a typical human has a surface area of 2 m^2, that's around one thermal photon every ten seconds in the visible spectrum. This is many more than 1,000 times too dim to see. The photons referred to in the article come from chemical reactions, not thermal radiation.
  • by smellsofbikes (890263) on Thursday July 23, 2009 @03:44PM (#28799189) Journal
    Read about Planck's Law [wikipedia.org]. It predicts the distribution of photons by frequency dependent on temperature. The scale is from wavelength = 0 to wavelength = inf, but the distribution is an asymmetric peak that goes to shorter wavelengths as the temperature increases. The extremely large majority of photons emitted by an object at 293K will be in the infrared, but a few will be visible, ultraviolet, and x-ray.
  • by Chris Burke (6130) on Thursday July 23, 2009 @03:47PM (#28799227) Homepage

    And you're playing a semantic trick where you take a word with multiple definitions, and change the definition you're using from the one that was clearly implied by the original context.

    In the headline "People Emit Visible Light", "Visible" means "in the visible portion of the spectrum". "Visible Light", especially in a scientific context, usually means "light which is in the visible portion of the spectrum".

  • by AndersOSU (873247) on Thursday July 23, 2009 @03:47PM (#28799231)

    not a bell curve [wikipedia.org]

    But it is a distribution, and the human body does radiate some visible photons. This phenomenon, however, is theorized not thermal radiation, but as something else.

  • by clone53421 (1310749) on Thursday July 23, 2009 @03:49PM (#28799273) Journal

    A flu mask is really only effective at stopping yourself from spreading germs when you're sick. It isn't really going to help keep you from getting sick from other people's germs.

  • by interkin3tic (1469267) on Thursday July 23, 2009 @03:58PM (#28799367)

    The summary, most commenters, and largely the article itself seem to be missing the big point here

    The researchers found the body glow rose and fell over the day, with its lowest point at 10 a.m. and its peak at 4 p.m., dropping gradually after that. These findings suggest there is light emission linked to our body clocks, most likely due to how our metabolic rhythms fluctuate over the course of the day...

    Since this faint light is linked with the body's metabolism, this finding suggests cameras that can spot the weak emissions could help spot medical conditions

    So yes, people glow, and yes, this was known previously. The point of the research is that this can be used, for studying circadian rythms and maybe identifying problems with it and metabolism. The scientist quoted is billed as a "circadian rhythm biologist," you've got to think he's probably not studying this to find out if people glow or not.

    The information in the summary is thirdhand at best: whoever makes the summary makes it from an article, which in this case wasn't primary literature from the actual scientists but was AOL news or whoever "imaginova corp" is interviewing several japanese scientists about their work. AOL news seems to have misunderstood the research that they were writing about.

  • by geekboy642 (799087) on Thursday July 23, 2009 @04:01PM (#28799405) Journal

    You lie. That film had ONE main part. Any evidence of some kind of 'sequel' was planted by the machines to confuse your mind.

  • by momerath2003 (606823) * on Thursday July 23, 2009 @04:05PM (#28799453) Journal

    The chance of emission at higher energies decreases exponentially. You're getting far, far, far more exposure to ionizing radiation from the naturally radioactive potassium in others' bodies than by their black-body emission.

  • by Chris Burke (6130) on Thursday July 23, 2009 @04:09PM (#28799499) Homepage

    I don't think that's obvious... well, other than the fact that they don't emit visible light by the definition I'd normally assume was meant. Since I can look around and see that they don't...

    It's extremely obvious if you're aware of the meaning of "visible light" in a scientific context. Anytime you see the phrase "visible light" in the same sentence as "scientists say" or "researchers have shown", then it is nearly 100% certain that this is the intended meaning. The clincher would be if you consider the layman's definition of "visible", realize that this is clearly not true, then consider the scientific definition and realize it is the only one that makes sense. Of course this still depends on knowing the scientific definition.

    And I'll admit I'm rather shocked that so many /.ers apparently don't know that meaning of the phrase "visible light". I know we have a more diverse background than we used to, but I still figured the average slashdotter was likely to have gotten a science degree where basic physics was a requirement, or at least have payed more attention than normal in high school physics or even just read the many science/astronomy related articles posted here, or read xkcd, or something.

    It made more sense to me when I just assumed people were being pedantic dicks. :P

  • by Roger W Moore (538166) on Thursday July 23, 2009 @04:20PM (#28799653) Journal
    Correct. Doing a quick back of the envelope calculation a human body will emit one photon with a wavelength of 600nm every 10 seconds. If we scale that up by a factor of 1,000 that would mean the human eye would need to be capable of seeing a flux of 100 photons/second per unit solid angle. This is well below the threshold of a human eye - you'd need a photomultiplier or low temp photon counter device to pick this up. So clearly this is not the source of light.
  • Re:Biblical? (Score:5, Informative)

    by Narcocide (102829) on Thursday July 23, 2009 @04:24PM (#28799705) Homepage

    They aren't, as such. What we know as a "halo" is more of a Hanna-Barbera cartoon knock-off of something that appears in a lot of early Christian art as a nimbus - a sort of glowing aura around Jesus and sometimes an accompanying Lamb. According to this wikipedia page [wikipedia.org] the concept was used earlier in a lot of other historical religious art too before becoming bastardized by pop culture's somewhat clumsy literal interpretation.

  • by Chris Burke (6130) on Thursday July 23, 2009 @04:39PM (#28799903) Homepage

    And you're assuming that Slashdot headlines are viewed as Scientific forum (capitalization used to emphasize your bias).

    When the sentence containing the phrase in question also includes the phrase "scientists reveal" and the next sentence includes "researchers show", then it is probably safe to interpret it in a scientific context.

    I will admit that I am biased towards thinking that most slashdotters would have attended and been interested enough to pay attention to high school or entry-level college physics. I realize that's not true. I guess I'm just really surprised that the term "visible light" is outside so many /.ers experience.

    Slashdot is not a scientific forum, but a nerd-emphasised general forum.

    Uh-huh. And one common attribute of nerds -- at least a virtue of anyone who I would call a nerd as a compliment -- is the desire to learn. When I read articles on /. about things not in my area of expertise, I often learn things from the article and from other readers who are familiar with the terms and phrases used in the article. It's one of the more enjoyable aspects of this forum.

    And now you know what "visible light" means in a scientific context. That's the most common context for that phrase, by the way. When talking in layman's terms, using "visible" to describe "light" would generally be redundant. Nobody would say "Then I saw a visible light shining through the woods."

    Slashdot may not be a scientific forum, but there are a lot of science articles on it. So you should be prepared to see scientific terms and to interpret them in a scientific context. You should probably not be upset when a scientific article uses scientific terms.

    Thus the common or vernacular definition should always be used, and the editors should remember that headlines are summaries of the article and stand alone frequently without further explanation.

    Okay, so next time an article mentions "infrared", it should instead specify "electromagnetic radiation with wavelengths between 750 nm and 100 m" so that readers don't say "What's infrared? I know from latin that 'infra' means 'below', but what's 'below' red? Maroon? Fuchsia?" Er, but wait, "electromagnetic" and "wavelength" don't aren't vernacular in any way... So no science terms? No technical terms? How do you even describe what this article is about using only vernacular definitions?

    Look, I don't understand a lot of legal terms (for one example among many), but I'm not about to ask that every YRO article avoids using them, or kvetch about it when I fail to comprehend a term and am corrected.

  • Re:link to paper (Score:2, Informative)

    by FleaPlus (6935) on Thursday July 23, 2009 @05:10PM (#28800307) Journal

    I'm a little worried that their first reference is Fritz-Albert Popp, who's kind of a pseudoscientific quack and into biophotonics [wikipedia.org], which is often used to try to validate things like homeopathy [hpathy.com].

  • by Anonymous Coward on Thursday July 23, 2009 @05:10PM (#28800313)

    Close. A single photon is capable of making a single cell (rod) in your retina fire. To actually perceive light, you need around 9 or 10 rods to fire at around the same time. Problem here is that only around 10% of the photons entering your eye end up striking a receptor - the rest are reflected off of the cornea, get absorbed in the vitreous humor (fluid inside the eye), or pass through the retina without striking a spot where a receptor is located.

  • Re:Biblical? (Score:5, Informative)

    by rumith (983060) on Thursday July 23, 2009 @05:19PM (#28800425)
    Usually "visible light" means "electromagnetic radiation with wavelength lying in (approximately) 380-750nm range". At least that's what they taught us in the university. Somehow, I find this definition much more logical than yours, no offense meant.
  • Re:Biblical? (Score:5, Informative)

    by Chris Burke (6130) on Thursday July 23, 2009 @05:52PM (#28800773) Homepage

    Also a lot of people don't know this but the Super Devil doesn't appear anywhere in the Bible.

  • Re:Biblical? (Score:2, Informative)

    by Anonymous Coward on Thursday July 23, 2009 @05:54PM (#28800799)

    If there are people who have vision that is 1,000 times normal, then they must get blinded by the sun really easily...

    Poor dogs! I hear that their sense of smell is something like 5000 times more sensitive than ours. They must not be able to smell anything when there is a strong aroma!

    Or thing of the cats who can see "in the dark". Well it's not really the dark it's just thousands of time less bright than daylight. Which means that in the daytime they must get blinded!

    Should I continue? :)

  • Re:Biblical? (Score:3, Informative)

    by BikeHelmet (1437881) on Thursday July 23, 2009 @06:55PM (#28801449) Journal

    You don't even have to assume some people are more sensitive to light, and can "see" it.

    There was a study a while ago about conscious and subconscious sight. Apparently certain kinds of blindness leave subconscious vision semi in-tact, so although the person couldn't see, he could snap his eyes shut if a bug was about to hit them.

    "Halos" might not even be literal halos, so much as a feeling you get when looking at someone.

    Your subconscious doesn't have a lot of ways to communicate. It's limited to feelings and reactions, mostly? I think this could all be processed subconsciously, so that our conscious mind would never know.

  • by Roger W Moore (538166) on Friday July 24, 2009 @01:07AM (#28803721) Journal
    Ah - but you are forgetting the solid angle. My rate is 100 photons/second/per steradian. I have no idea how small a rod is but probably on the 1 micrometre? (it has to be bigger that the wavelengths it detects which are 100's of nm). Hence you would have to place your retina within ~5 micrometres of the source for each rod to subtend a solid angle of 0.01 steradians to get one photon a second - which the article says that you still won't be conscious of - particularly since at this point you've rammed the source into your eyeball!
  • Re:Biblical? (Score:2, Informative)

    by shadanan (806810) on Friday July 24, 2009 @03:59AM (#28804501) Homepage

    The retina of the eye contains two types of light sensitive cells: cones and rods. The cones [wikipedia.org] are responsible for the eye's ability to distinguish colour and function well in good lighting conditions. The cones are further broken down into three types of cones, each sensitive to one of the three primary colours. The rods [wikipedia.org] are responsible for providing vision when the ambient lighting is low. There is only one type of rod. As a result, when observing in very low light conditions, the eye can only see in black and white.

    The rods are located near the outer edges of the retina. This is why very distant stars that are barely visible appear brighter if you use your peripheral vision to view them by looking off to the side.

  • Re:Biblical? (Score:2, Informative)

    by phatslaab (1046786) on Friday July 24, 2009 @10:09AM (#28806567)
    Well-spoken. The word Satan is a title or description, not a name originally given to the angel now known as Satan. We may never know his original name. Perhaps it is because biblical names have special meaning and the angel now known as Satan does not live up to his former name. Reminds me though of people who use the word "God" as if it is a name. Most people either don't know or don't care what God's real name is.
  • Re:Biblical? (Score:2, Informative)

    by phatslaab (1046786) on Friday July 24, 2009 @10:14AM (#28806611)
    Sorry, Job is actually the 4th, 5th, or 6th oldest book. Genesis, Exodus, & Leviticus were all written prior but Numbers, Deuteronomy, & Job were all completed in the same year - circa 1473 BCE.

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