Shortest Non-Ionizing Wavelength for human body at any intensity/duration?

Radium

Hi:

What is the shortest wavelength at which light is completely
non-ionizing to any and all parts of the human body regardless of
duration of exposure or intensity of the light? From my own research I
guess its 400nm but I could be wrong.

Thanks,

Radium

Tom Roberts

Radium wrote:
> What is the shortest wavelength at which light is completely
> non-ionizing to any and all parts of the human body regardless of
> duration of exposure or intensity of the light?

Given your absolute conditions, the shortest wavelength that meets your
criteria is infinite.

In general, X-rays and shorter-wavelength radiation can ionize
essentially any atom or molecule, and radio waves and longer-wavelength
radiation cannot ionize any atom or molecule, except for extremely high
intensity radiation for which multiple photons can "gang up" on a single
electron -- this makes the rate of ionization be many orders of
magnitude lower (so much so that in practice it can be ignored), but is
still not "completely non-ionizing".

Ultraviolet radiation can ionize some molecules.

Note that biological effects do not always require ionization, and your
eyes can see without the sensing nerves being ionized, all that is
required is enough energy to make the state change that fires the neuron
[#]. I believe that sunburn is ionization; I'm not sure about suntanning.

[#] Part of this depends on what one means by "ionization" --
the electrons are definitely pushed around the molecule, but
don't leave it; so some atom within the molecule is "ionized"
but the molecule itself is not. Sight is due to a chemical
change in the sensing molecules, not a current generated by
ionization. I believe it takes a few dozen molecules within
~0.1 second to generate a large enough signal to fire the
neuron.

Note also that non-ionizing radiation can cause biological damage via
heating. The radiation from your microwave oven cannot ionize normal
biological molecules (it works by inducing resonant vibrations in water
molecules)....

> From my own research I
> guess its 400nm but I could be wrong.

Above that wavelength the rate of ionization falls off quite rapidly,
but never to "completely non-ionizing" (see above). Note the rate of
ionization at a given wavelength depends rather strongly on which atom
or molecule is involved.

Tom Roberts

CoarseAdjust

Tom Roberts wrote:
> Radium wrote:
> > What is the shortest wavelength at which light is completely
> > non-ionizing to any and all parts of the human body regardless of
> > duration of exposure or intensity of the light?
>
> Given your absolute conditions, the shortest wavelength that meets your
> criteria is infinite.
>
> In general, X-rays and shorter-wavelength radiation can ionize
> essentially any atom or molecule, and radio waves and longer-wavelength
> radiation cannot ionize any atom or molecule, except for extremely high
> intensity radiation for which multiple photons can "gang up" on a single
> electron -- this makes the rate of ionization be many orders of
> magnitude lower (so much so that in practice it can be ignored), but is
> still not "completely non-ionizing".
>
> Ultraviolet radiation can ionize some molecules.
>
> Note that biological effects do not always require ionization, and your
> eyes can see without the sensing nerves being ionized, all that is
> required is enough energy to make the state change that fires the neuron
> [#]. I believe that sunburn is ionization; I'm not sure about suntanning.
>
> [#] Part of this depends on what one means by "ionization" --
> the electrons are definitely pushed around the molecule, but
> don't leave it; so some atom within the molecule is "ionized"
> but the molecule itself is not. Sight is due to a chemical
> change in the sensing molecules, not a current generated by
> ionization. I believe it takes a few dozen molecules within
> ~0.1 second to generate a large enough signal to fire the
> neuron.
>
> Note also that non-ionizing radiation can cause biological damage via
> heating. The radiation from your microwave oven cannot ionize normal
> biological molecules (it works by inducing resonant vibrations in water
> molecules)....
>
> > From my own research I
> > guess its 400nm but I could be wrong.
>
> Above that wavelength the rate of ionization falls off quite rapidly,
> but never to "completely non-ionizing" (see above). Note the rate of
> ionization at a given wavelength depends rather strongly on which atom
> or molecule is involved.
>
> Tom Roberts

I'd put it at much longer than that. Basically, as long as there is a
dipole in the anatomy (or part of the anatomy) that can absorb
radiation, you can get a burn from it. A burn is usually accompanied
by, if not the result of, a great deal of free radical fromation
(molecular ions), and that is something that even some amateure radio
enthusiasts might have experienced from touching a 100 Watt transmitter
antenna at 80 meters or even longer. Water as moisture in the skin
being the primary absorber in the microwave and RF cases.

Frank P. Auteri

jwill@BasicISP.net

Tom Roberts wrote:
> Radium wrote:
> > What is the shortest wavelength at which light is completely
> > non-ionizing to any and all parts of the human body regardless of
> > duration of exposure or intensity of the light?
>
> Given your absolute conditions, the shortest wavelength that meets your
> criteria is infinite.
>
> In general, X-rays and shorter-wavelength radiation can ionize
> essentially any atom or molecule, and radio waves and longer-wavelength
> radiation cannot ionize any atom or molecule, except for extremely high
> intensity radiation for which multiple photons can "gang up" on a single
> electron -- this makes the rate of ionization be many orders of
> magnitude lower (so much so that in practice it can be ignored), but is
> still not "completely non-ionizing".
>
> Ultraviolet radiation can ionize some molecules.
>
> Note that biological effects do not always require ionization, and your
> eyes can see without the sensing nerves being ionized, all that is
> required is enough energy to make the state change that fires the neuron
> [#]. I believe that sunburn is ionization; I'm not sure about suntanning.

Yes. Conformational changes in a rhodopsin derived molecule
in the photoreceptors causes initiation of visual response to light.
This molecular-level change does not require ionization, so the
specious dichotomous criterion of either "ionization" or "heating" as
the only causes of biological effect from electromagnetic radiation
is obviously false.

Many persons with only a very basic knowledge of the biology assert
that ionization and heating are the only possible effects of EM
radiation;
therefore, the only possible effect of microwave radiation relevant to
biological function must be "heating" of one kind or another. This
clearly is ignorant and false, because all visible light is nonionizing
and nonheating.

Lord preserve us from the idle speculations of ignorant physicists
and electrical engineers!

For example, just as prolonged exposure to loud but not
immediately harmful sounds will cause deafness, so also will
prolonged exposure to blue light in the visible range cause loss
of the blue-yellow color system -- permanent damage similar in
effect (but not in obvious injury) to exposure to light
from an arc welder. This blue light is nonionizing (say, 480 nm
wavelength); yet, it apparently irreversibly damages the blue
cone photoreceptors. Mixing exposure to blue with exposure
to white light or other color mixtures prevents the damage.

To answer your question about effects on the skin, ultraviolet
radiation is required both for tanning and for sunburn.
Tanning is a response to skin damage caused by ionizing
radiation. I am not certain of the mechanism,
but I believe specific byproducts of the damage trigger
melanocyte growth, leading to a darkening of the upper
dermis.
The absorption of ionizing radiation (and conversion to heat)
in the darkened upper layers then protects the
lower layers (and underlying blood vessels or muscle) from
subsquent radiation exposure.

> ...
> Tom Roberts

Timo A. Nieminen

On Sun, 31 Dec 2006, jwill@BasicISP.net wrote:

> Many persons with only a very basic knowledge of the biology assert
> that ionization and heating are the only possible effects of EM
> radiation;
> therefore, the only possible effect of microwave radiation relevant to
> biological function must be "heating" of one kind or another. This
> clearly is ignorant and false, because all visible light is nonionizing
> and nonheating.

Certainly _not_ nonheating. The energy doesn't just disappear when the
light does.

Capable of biological effect through mechanisms other than ionisation and
heating, yes. However, I suspect that most of these effects include
heating as a side effect. The heating isn't always biologically
significant, so perhaps it's a pedantic point. OTOH, given that many
organisms deliberately exploit the heating effects of visible light ...

However, it's not stupid to claim that the only significant biological
effect of microwave radiation is heating, at typically encountered
intensities. Perhaps wrong, but not stupid - compare energy per photon to
thermal energies at room temperature. What will a single photon do?

Of course, there's more to EM radiation than photons - namely, electric
and magnetic fields, and these can have a wide range of effects. Some
years ago, I saw some nice photos of elongated E. coli - put them in
an AC field of the right frequency and amplitude, and they stop dividing.
They keep growing longer and longer. But at this point, you can stop
bothering about photons, or absorption of single photons. It's also not
typical RF exposure.

If you're willing to extend "biological effects" to include behaviour,
then clearly there are non-ionising, non-heating effects in the visible,
as shown by, eg TV, photos, art, etc.

--
Timo Nieminen - Home page: http://www.physics.uq.edu.au/people/nieminen/
E-prints: http://eprint.uq.edu.au/view/person/...,_Timo_A..html
Shrine to Spirits: http://www.users.bigpond.com/timo_nieminen/spirits.html