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People Emit Visible Light
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."
I thought this was discovered and establish in 2005 by Mitsuo Hiramatsu, a scientist at the Central Research Laboratory at Hamamatsu Photonics. 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?
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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.
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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.
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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.
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See Planck's law. 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.
Read about Planck's Law. 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.
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not a bell curve
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.
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The summary, most commenters, and largely the article itself seem to be missing the big point here
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.
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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.
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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.
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 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.
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.
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.
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