sunscreen makes you hotter?

[larry english]

i was wondering how sunscreen works.

about all i can find out is that it seems to trap and absorb the uv
radiation before it gets to your skin.

but the heat from absorption still does.

so my question is, wouldn't that make you hotter than not using sunscreen?

or is it the same, i.e., if you weren;t using it, the skin would
absorb the uv anyway...?

seems like it would be better to invent a sunscreen that would
reflect the uv away, rather than absorb it.

wle.

[Bob Denton]

On 31 Jul 2003 06:33:29 -0700, (larry english) wrote:

>i was wondering how sunscreen works.
>
>about all i can find out is that it seems to trap and absorb the uv
>radiation before it gets to your skin.
>
>but the heat from absorption still does.
>
>so my question is, wouldn't that make you hotter than not using sunscreen?
>
>or is it the same, i.e., if you weren;t using it, the skin would
>absorb the uv anyway...?
>
>seems like it would be better to invent a sunscreen that would
>reflect the uv away, rather than absorb it.
>
>wle.
UV doesn't make you hot. It's infra red and visible light.
Bob Denton
Gulf Stream International
Delray Beach, Florida
www.sinkthestink.com
Manufacturers of Sink the Stink

[Bill Davidson]

Bob Denton wrote:
> UV doesn't make you hot. It's infra red and visible light.

I'm pretty sure that's not true. Any time you absorb radiation,
you get heat. In other words, they all make you hot. It's
possible that UV results in less heat but even that I doubt.

Why does UV filtering (tint) on windows reduce the heat buildup
inside a car or building; even if it's a very light tint?

--Bill Davidson
--
Please remove ".nospam" from my address for email replies.

I'm a 17 year veteran of usenet -- you'd think I'd be over it by now

[Tim McNamara]

In article <eMdWa.33166$Ne.31813@fed1read03>,
Bill Davidson > wrote:

> Bob Denton wrote:
> > UV doesn't make you hot. It's infra red and visible light.
>
> I'm pretty sure that's not true. Any time you absorb radiation,
> you get heat. In other words, they all make you hot. It's
> possible that UV results in less heat but even that I doubt.

If all radiation absorption results in heating equally, why don't
microwaves use UV frequency light and use radio waves instead?

From www.howstuffworks.com:

> A microwave oven uses microwaves to heat food. Microwaves are radio
> waves. In the case of microwave ovens, the commonly used radio wave
> frequency is roughly 2,500 megahertz (2.5 gigahertz). Radio waves
> in this frequency range have an interesting property: they are
> absorbed by water, fats and sugars. When they are absorbed they are
> converted directly into atomic motion - heat. Microwaves in this
> frequency range have another interesting property: they are not
> absorbed by most plastics, glass or ceramics. Metal reflects
> microwaves, which is why metal pans do not work well in a microwave
> oven.

UV light only penetrates the skin about 1 mm, but this is deeper than
visible light penetrates. This is where the basal layer of the skin
is found (and where basal cell carcinomas start). Much of the visble
light spctrum is simply reflected from the skin and is not absorbed.
Sunscreen places an absorptive barrier specific to UVa and UVb
radiation above the skin, so it is absorbed or blocked before it gets
to the skin.

The shorter the wavelength, the more energy light has. Therefore UV
has more energy than visible light. As the wavelength of
electromagnetic radiation decreases, the radiation can be more
penetrative and damaging to living tissue (X rays and gamma rays).
These are not as readily absorbed by tissue and cause less heating as
a result. X rays pass through soft tissue readily, but tend to be
absorbed by bone, and can be captured on photographic film. Gamma
rays pass through hard tissue as well (and thus tend to be destructive
of bone marrow, for example).

Longer wavelengths such as microwaves and radio waves are more
absorbable (sp?), hence their use in microwave ovens to heat food.

> Why does UV filtering (tint) on windows reduce the heat buildup
> inside a car or building; even if it's a very light tint?

I suspect- but don't know- that heat gain through a transparent
surface such as window glass, with subsequent heating of the air
volume enclosed by the windows, is a matter of different wavelengths
than is the case with skin. Air absorbs different frequencies of
light and refiects none, unlike skin. Ditto the metal of a car body,
the brick of a wall, or the fibers of upholstery.

UV tinting is primarily used to prevent fading of upholstery and
doesn't- by itself- result in much reduction of solar (heat) gain
because the other frequencies are selectively unfiltered. Just as in
the case of UV photographic filters, which are nearly colorless, UV
tinted auto glass serves to improve long-distance vision by filtering
at the blue end of the visible spectrum. Blue light scatters more
easily in Earth's atmosphere than the longer wavelengths, causing
blurring of vision.

We probably see the small portion of the electromagentic spectrum that
we do because a broader spectrum could not be focused on the retina as
well. Even within the range of frequencies we can visually perceive,
the focal length for the short end of the visible spectrum is slightly
different than the focal length for the long end.

As far as sunscreen making one feel hotter- my subjective impression
is that I feel hotter with sunscreen on. I suspect this is due to the
oil base that most sunscreens use, which reduces the "wind chill"
effect and puts an insulating layer between the skin and the sweat as
it evaporates. My skin is certainly much wetter with sweat when I
wear sunscreen.

[Terry Morse]

Tim McNamara wrote:

> If all radiation absorption results in heating equally, why don't
> microwaves use UV frequency light and use radio waves instead?

<snip>
>
> UV light only penetrates the skin about 1 mm,

You answered your own question: UV doesn't penetrate much and would
only heat the outer surface of the food. A kilowatt of UV would
transfer the same energy to the food as a kilowatt of microwave, but
the microwave would heat deeper.
--
terry morse, heat transfer specialist

[Øyvind Røtvold]

Tim McNamara > writes:

[snip]
> If all radiation absorption results in heating equally, why don't
> microwaves use UV frequency light and use radio waves instead?

A fair question.

[snip]
> UV light only penetrates the skin about 1 mm,

And there is the answer.

[snip]


>
> The shorter the wavelength, the more energy light has.

Nope, The shorter the wavelength, the more energy per photon The
amount of energy in a wave depends on ... the amount of energy in the
wave.

[snip]
>
> Longer wavelengths such as microwaves and radio waves are more
> absorbable (sp?), hence their use in microwave ovens to heat food.

IR waves will be absorbed in the outer layer of food, hence their use
in barbeque.

[snip]
> As far as sunscreen making one feel hotter- my subjective impression
> is that I feel hotter with sunscreen on. I suspect this is due to the
> oil base that most sunscreens use, which reduces the "wind chill"
> effect and puts an insulating layer between the skin and the sweat as
> it evaporates. My skin is certainly much wetter with sweat when I
> wear sunscreen.

Sweat will not evaporate as fast from a oily surface.

--
__o | Øyvind Røtvold
_`\(, | http://www.darkside.no/olr/index.html
(_)/(_) | ... biciclare necesse est ...

[ph_leung]

(larry english) wrote in message >...
> i was wondering how sunscreen works.
>
> about all i can find out is that it seems to trap and absorb the uv
> radiation before it gets to your skin.
>
> but the heat from absorption still does.
>
> so my question is, wouldn't that make you hotter than not using sunscreen?
>
> or is it the same, i.e., if you weren;t using it, the skin would
> absorb the uv anyway...?
>
> seems like it would be better to invent a sunscreen that would
> reflect the uv away, rather than absorb it.
>
> wle.

Sunblocks should reflect and not absorb as much as sunscreens. Look
for zinc oxide and titanium dioxide in the ingredients of block
lotions or sunscreens. Neutrogena SPF 30 Sensitive skin sunblock,
many "kids" SPF 25+ blocks, and zinc oxide pastes (look in baby diaper
ointment section of supermarket) are examples.
Most of these give the skin a whiter appearance after applying than
sunscreens.

[g.daniels]

adequate heat transfer from the body to the environemnt requires
radiators-the capillary network below the basal layer does this and a
skin layer mechanism.Different areas of your skin transmit varying
quantities of heat-the head throws of a lotta heat that comes from the
metabolic processes that drive your muscles ect.

"My skin is certainly much wetter with sweat when I
Ø wear sunscreen. UV doesn't make you hot. It's infra red and visible
light
Any time you absorb radiation,
Ø you get heat. In other words, they all make you hot.
www.howstuffworks.com:"

and this is all true but clogging the pores with sunscreen??? probably
cuts down on that areas heat transfer efficiency while reducing heat
absorption-all those photons banging the devil outa your chromosomes
and cuasing melanoma. which incidentlly increases with age and with
the wind burn effect fron cycling which sunscreen reduces especially
on the shins.

But the deal is that one only rubs the sunscreen on some body parts
not all and the other parts take up some of the slack.
if you're having problems with heat transfer then one might look at
psychologic quantifications of the problem over time-like eating
oatmeal before may mae you hot when eating bananas doesn't rather than
the sunscreen.
The botttom line(and try a split seat there) is conditioning for the
heat. ya gotta run run run in the heat to not be too hot. taking a
pill doesn't do it.
wqearing a wicking skull cap with clean short hair might help, wicking
socks and surely an adnaced textiles wicking t-shirt the more
expensive the better and if you're in AR going east at 3pm try an arab
neck scarf. and try coppertone.

[g.daniels]

color equals colr not heat!
neutrinos pass thru everything, see the Antarctic neutrino telescope
facing into the earth from an ice bed. (the possibilities of a deep
space tunnel emitting these particles with an eddy layer?)

[Werehatrack]

On 31 Jul 2003 06:33:29 -0700, (larry english) may
have said:

>i was wondering how sunscreen works.
>
>about all i can find out is that it seems to trap and absorb the uv
>radiation before it gets to your skin.
>
>but the heat from absorption still does.
>
>so my question is, wouldn't that make you hotter than not using sunscreen?
>
>or is it the same, i.e., if you weren;t using it, the skin would
>absorb the uv anyway...?

Esseantially, the latter is the case, but since the thermal load from
this source is almost certainly dwarfed by the thermal load from IR
and visible light conversion, I doubt that it would have a significant
effect.

>seems like it would be better to invent a sunscreen that would
>reflect the uv away, rather than absorb it.

Zinc oxide cream. Great stuff, if you like looking like a clown and
not being able to sweat from those pores.

--
My email address is antispammed;
pull WEEDS if replying via e-mail.
Yes, I have a killfile. If I don't respond to something,
it's also possible that I'm busy.

[Werehatrack]

On 3 Aug 2003 02:43:54 +0950, BaCardi >
may have said:

>What was the question?

Does sunscreen make you feel hotter, and why? Thread drift carried it
off into lala land as usual.

For the original question, my experience says "yes". As for why,
well, really, does it matter? There's not a lot of choice available;
use sunscreen, find shade, or stay inside.

--
My email address is antispammed;
pull WEEDS if replying via e-mail.
Yes, I have a killfile. If I don't respond to something,
it's also possible that I'm busy.

[Peter]

Joe Riel wrote:

> Werehatrack > writes:
>
>
>>Light and microwaves of the same frequency are not the same thing. A
>>microwave transmitter that is operating on the same wavelength as
>>visible light does not produce light.
>
>
> Bull****. The phenomenon is identical. Microwaves have a significantly
> higher wavelength then light, that is why we cannot seem them.
> The shortwest wavelength of a microwave is about 1cm.
> The longest wavelenght of visible light is less then a 1um,
> orders of magnitude longer.
^
I presume you meant to say "shorter" here. Yes, radio waves, microwaves,
light, X-rays, gamma rays are all elecromagnetic waves that differ in
wavelength.

[Werehatrack]

On Sat, 02 Aug 2003 21:59:29 GMT, Joe Riel > may
have said:

>Werehatrack > writes:
>
>> Light and microwaves of the same frequency are not the same thing. A
>> microwave transmitter that is operating on the same wavelength as
>> visible light does not produce light.
>
>Bull****. The phenomenon is identical. Microwaves have a significantly
>higher wavelength then light, that is why we cannot seem them.
>The shortwest wavelength of a microwave is about 1cm.
>The longest wavelenght of visible light is less then a 1um,
>orders of magnitude longer.

Infrared light ranges well above 1mm in wavelength. Microwaves range
down into that area. The ranges overlap. An IR filter which was
known to block the transmission of IR in that freq range had no effect
on the microwaves. Remember the existence of the wavicle known as a
photon, and the reason should become obvious. Yes, the two forms of
energy follow the same rules, but the conclusion is that they're not
the same.

As of last I heard, no tech was available to reliably modulate such a
signal or detect modulation beyond on/off, so it wasn't too useful.
That may have changed; this was a number of years ago. I'm told that
the limits of microwave freq generation have changed, but I don't know
what they are now.

None of this will make your bike work better.

--
My email address is antispammed;
pull WEEDS if replying via e-mail.
Yes, I have a killfile. If I don't respond to something,
it's also possible that I'm busy.

[Peter]

Werehatrack wrote:

> On Sat, 02 Aug 2003 21:59:29 GMT, Joe Riel > may
> have said:
>
>
>>Werehatrack > writes:
>>
>>
>>>Light and microwaves of the same frequency are not the same thing. A
>>>microwave transmitter that is operating on the same wavelength as
>>>visible light does not produce light.
>>
>>Bull****. The phenomenon is identical. Microwaves have a significantly
>>higher wavelength then light, that is why we cannot seem them.
>>The shortwest wavelength of a microwave is about 1cm.
>>The longest wavelenght of visible light is less then a 1um,
>>orders of magnitude longer.
>
>
> Infrared light ranges well above 1mm in wavelength. Microwaves range
> down into that area. The ranges overlap. An IR filter which was
> known to block the transmission of IR in that freq range had no effect
> on the microwaves. Remember the existence of the wavicle known as a
> photon, and the reason should become obvious. Yes, the two forms of
> energy follow the same rules, but the conclusion is that they're not
> the same.

No, Joe is correct that they are both electromagnetic waves and the only
difference is the wavelength. If the filter stopped electromagnetic waves
of a certain frequency then it makes no difference if we call those waves
IR or microwave. Perhaps this page will help you 'see the light.'

http://imagine.gsfc.nasa.gov/docs/science/know_l1/emspectrum.html

[Tim McNamara]

In article >,
Werehatrack > wrote:

> On Thu, 31 Jul 2003 15:40:46 -0500, Tim McNamara
> > may have said:
>
> >In article <eMdWa.33166$Ne.31813@fed1read03>,
> > Bill Davidson > wrote:
> >
> >> I'm pretty sure that's not true. Any time you absorb radiation,
> >> you get heat. In other words, they all make you hot. It's
> >> possible that UV results in less heat but even that I doubt.
> >
> >If all radiation absorption results in heating equally, why don't
> >microwaves use UV frequency light and use radio waves instead?
>
> Light and microwaves of the same frequency are not the same thing.

Umm, the question was rhetorical, in response to the post which I
quoted. I knew the answer. But thanks to the three or four people
who answered anyway.

> >I suspect- but don't know- that heat gain through a transparent
> >surface such as window glass, with subsequent heating of the air
> >volume enclosed by the windows, is a matter of different
> >wavelengths than is the case with skin.
>
> Any incident photonic radiation which reaches the interior of a
> car, regardless of its wavelength, may be absorbed and converted to
> heat, just as with light hitting skin; a car's interior, however,
> has much less ability to shed that heat unless the car's engine is
> running and the A/C is operating, while skin can sweat. Most of
> the light that gets to the surface of the planet isn't UV, so the
> UV component is not the major player in car interior heating or
> skin heating, but UV (as you noted) has other tricks to play with
> skin.
>
> Most window glass will block some UV, but usually far from all of
> it. A photographic UV filter looks like just a piece of clear
> glass, but it blocks 100% of UV. Visibly tinted glass doesn't
> necessarily block UV, but it reduces the amount of visible light
> that gets through, thus reducing the amount of heat produced by the
> light-absorptive surfaces inside. The light that is blocked at the
> glass translates largely into heat that is shed back to the
> environment on the outside of the glass, and thus does not
> significantly contribute to interior heating. The majority of the
> light which gets through the glass is absorbed by, and therefore
> heats, the surfaces inside. Some of the light is reflected by the
> interior surfaces; if the reflection is back out of the window, the
> heat load is not increased. If it's reflected to another interior
> surface, the light may still contribute to interior heating. In
> being reflected, of course, there is some heat produced since the
> reflection is never 100%.

Thanks, that's pretty much as I suspected.

[Prometheus]

Being from southern california, and a swimmer/water polo
player/general pool and beach bum, i feel obligated to contribute to
the sunscreen debate.

Having gone out both with and without sunscreen for physical activity,
in high sunlight environments (water surfaces reflect a good deal of
light, forcing to fight the UV war on two fronts), I say a few things:

1. alcohol based sunscreen (bullfrog quick-dry). non-greasy, and
doesn't get your hands all yucky. if not that, then regular bullfrog
is less messy than all the others. (its also so slick that its as
greasy as you can get without being illegal for sports).
2. I've actually been hotter WITHOUT the sunscreen than with. then
again, i don't feel heat so much as I feel sweat, so maybe I sweat
more without the sunscreen.
3. the best thing you can do to protect from the sun is a shirt
(polypropylene,cycling jerseys, and the like are the best for sun/UV
protection) and a big floppy hat. zinc oxide is messy, so is titanium
dioxide, and they're hard to get right, cuz you really have to slop it
on there, then sweat screws it up big time.

[Ignatz Q. Mouse]

BaCardi wrote:
> Its pretty simple really. Sunscreen DOES make you feel hotter. You put
> on a layer of sunscreen. Well duh. Common sense. Its going to be hotter
> than not having a layer of sunscreen on.

Doesn't sound at all like common sense as it does an assumption.

There's really two parts to the original question:

1. Does it make you 'feel' hotter?
2. Does it impede cooling, thus making you hotter?

If I rub on something that's a mild skin irritant, or becomes one during
the ride due to the sunscreens exposure to perspiration, light and heat,
I may think I'm hot, where I'm actually the same skin surface temperature.

Any compound which holds water to the skin surface, by it's own surface
tension or bonding with water molecules could reduce the efficiency of
cooling through evaporization. (Turning water liquid to water vapor is
exothermic, taking away body heat, this is why your arm feels cool for a
moment after an alcohol swabbing.)

Perhaps some actual empirical tests should be peformed, rather than
simply hazarding guesses.

[Eric]

HUH? Better tell those guys sending information to your house. CATV
uses AM fiber optic cable (at 1310 or 1550nm) for the last mile. If
you're a dish subscriber, you get QPSK digital microwave (KA band)
data.

Don't even want to get started on all those modulation methods for
phone calls...

Seems to work well enough.

Eric

Werehatrack > wrote in message >...
> On Sat, 02 Aug 2003 21:59:29 GMT, Joe Riel > may
> have said:
>
> >Werehatrack > writes:

> As of last I heard, no tech was available to reliably modulate such a
> signal or detect modulation beyond on/off, so it wasn't too useful.
> That may have changed; this was a number of years ago. I'm told that
> the limits of microwave freq generation have changed, but I don't know
> what they are now.
>
> None of this will make your bike work better.

[JP]

BaCardi > wrote in message >...
> Uhhh, it's like putting on clothes. The more you put on the
> hotter you get.

No, it's not like clothes, which don't necessarily make you hotter, either, BTW.

[Sorni]

"BaCardi" > wrote in message
...

> Uhhh, it's like putting on clothes. The more you put on the
> hotter you get.

That's why sunscreen sales soar in the dead of winter!

Logical Bill

[Precious Pup]

Tim McNamara wrote:
>
> In article <eMdWa.33166$Ne.31813@fed1read03>,
> Bill Davidson > wrote:
>
> > Bob Denton wrote:
> > > UV doesn't make you hot. It's infra red and visible light.
> >
> > I'm pretty sure that's not true. Any time you absorb radiation,
> > you get heat. In other words, they all make you hot. It's
> > possible that UV results in less heat but even that I doubt.
>
> If all radiation absorption results in heating equally, why don't
> microwaves use UV frequency light and use radio waves instead?


For a photon:

E(f) = h_cross*f

So if the energy is indeed _absorbed_ (not reflected, or...?), then photon for photon, higher frequency does
mean more heating.

I seem to recall a belief that the water molecule was "resonant" at some frequencies. If so then coupling
energy into them may be more effective at some frequencies than others (both higher and lower than resonance
might be less effective). For example: 2.4 GHz. Sorry about the mights and maybes; that is all you get for
an expedient response that *may* not be accurate. I'm not a specialist there.

[Precious Pup]

Werehatrack wrote:
>
> On Thu, 31 Jul 2003 15:40:46 -0500, Tim McNamara
> > may have said:
>
> >In article <eMdWa.33166$Ne.31813@fed1read03>,
> > Bill Davidson > wrote:
> >
> >> Bob Denton wrote:
> >> > UV doesn't make you hot. It's infra red and visible light.
> >>
> >> I'm pretty sure that's not true. Any time you absorb radiation,
> >> you get heat. In other words, they all make you hot. It's
> >> possible that UV results in less heat but even that I doubt.
> >
> >If all radiation absorption results in heating equally, why don't
> >microwaves use UV frequency light and use radio waves instead?
>
> Light and microwaves of the same frequency are not the same thing.


This is a nonsensical statement.

> A
> microwave transmitter that is operating on the same wavelength as
> visible light does not produce light.

As was that. Microwave != visible light, by definition.

Microwave is defined: 300 MHz to 300 GHz. However, most microwave engineers don't seem to consider it
"microwave" until about 1 GHz, due to the fact that they can more or less get away with *point form*
components below 1 GHz as opposed to the more accurate but more unwieldy *distributed form* used as the
frequency climbs.


> >I suspect- but don't know- that heat gain through a transparent
> >surface such as window glass, ...

Anyone who can figure out that "heat gain" thing ought to patent it and become the richest human ever.

> Any incident photonic radiation which reaches the interior of a car,
> regardless of its wavelength, may be absorbed and converted to heat,...

This much is true. In essence, tinted windows reduce transmission (reflect or absorb) to the interior of
certain spectral components, so naturally the total photon energy reaching the inside of the car will be less
with tinted windows.

[Steve Maas]

This is a joke, right?

In any case, light, microwaves, radio waves are all electromagnetic
radiation. The only difference is wavelength (or, if you prefer,
frequency). This is basic physics.

Solar energy is largely black-body radiation at about 5600K, which peaks
at a wavelength around 1 micron, in the infrared. Not that it
matters--the issue is cooling, not heating. We know that we get hot
while bicycling. What else do you need to know?

A thin layer of sunscreen provides a trivially insignificant amount of
insulation. Most of your cooling comes from evaporating sweat anyway,
not conductive heat transfer through your skin, so the effect of
sunscreen is negligible.

By the way, if you're really wondering why ovens use microwaves instead
of UV, aside from the fact that the UV would blind everyone, what would
you use for an economical source of 1500W UV energy?



Werehatrack wrote:

>
>
> Light and microwaves of the same frequency are not the same thing. A
> microwave transmitter that is operating on the same wavelength as
> visible light does not produce light. (Although the results of the
> original experiment demonstrating this of which I'm aware were not
> published due to the nature of the research facility in which they
> were carried out at the time, the result was not unexpected; no
> physicist that I've told about it was surprised, and the average
> reaction was of the "Well, duh!" variety.) A microwave transmitter
> may produce electromagnetic radiation at light frequencies, but it
> will not produce light. If this were not the case, a "light receiver"
> could be tuned to a convenient frequency and used for solar radiation
> collection with incredible efficiency. Unfortunately, it doesn't
> work, because light isn't electromagnetic. (Sadly, Popular Science,
> high school science texts, and the writers of that caliber have yet to
> come to grips with the distinction.)
>
>

[Chris]

"Steve Maas" > wrote in message
...
> This is a joke, right?
>
> In any case, light, microwaves, radio waves are all electromagnetic
> radiation. The only difference is wavelength (or, if you prefer,
> frequency). This is basic physics.
>

What if the biggest influence is that it interferes with your sweat and its
job in cooling your body? Would it still be a joke?

> Solar energy is largely black-body radiation at about 5600K, which peaks
> at a wavelength around 1 micron, in the infrared. Not that it
> matters--the issue is cooling, not heating. We know that we get hot
> while bicycling. What else do you need to know?
>
> A thin layer of sunscreen provides a trivially insignificant amount of
> insulation. Most of your cooling comes from evaporating sweat anyway,
> not conductive heat transfer through your skin, so the effect of
> sunscreen is negligible.
>
> By the way, if you're really wondering why ovens use microwaves instead
> of UV, aside from the fact that the UV would blind everyone, what would
> you use for an economical source of 1500W UV energy?
>
>
>
> Werehatrack wrote:
>
> >
> >
> > Light and microwaves of the same frequency are not the same thing. A
> > microwave transmitter that is operating on the same wavelength as
> > visible light does not produce light. (Although the results of the
> > original experiment demonstrating this of which I'm aware were not
> > published due to the nature of the research facility in which they
> > were carried out at the time, the result was not unexpected; no
> > physicist that I've told about it was surprised, and the average
> > reaction was of the "Well, duh!" variety.) A microwave transmitter
> > may produce electromagnetic radiation at light frequencies, but it
> > will not produce light. If this were not the case, a "light receiver"
> > could be tuned to a convenient frequency and used for solar radiation
> > collection with incredible efficiency. Unfortunately, it doesn't
> > work, because light isn't electromagnetic. (Sadly, Popular Science,
> > high school science texts, and the writers of that caliber have yet to
> > come to grips with the distinction.)
> >
> >
>

[Terry Morse]

Steve Maas wrote:

> My source [for solar radiation] is the curves in Radio Astronomy by
> John Krauss. Take a look at them; I think you'll find that the peak
> is fairly broad.

[Wish you wouldn't top post, it makes following a discussion
difficult]

Here's my most convenient source:

Roshenow et al, _Handbook of Heat Transfer_, 1998, p. 7.5:

"the solar radiation spectrum has a peak at about [lambda] = 0.5
[microns], as T(sun) = 5762 k"

Those curves you are looking at are probably on a log scale, making
the distribution look wider than it is. Using the Planck
distribution equation, the sun's energy at 1 micron is only 41% of
its energy at 0.5 micron. Not a big difference on a log scale, but a
substantial difference in energy.
--
terry morse Palo Alto, CA http://www.terrymorse.com/bike/

[dookie]

save the technobabble...

as a strawberry blonde who relies heavily on his sunscreen i absolutely
guarantee you that sunscreen is less hot than a 1st or 2nd degree burn.

and while i'm spouting...the new alchohol-based 'gel' formulas absoultely
blow the old lotion-style formulas away in terms of comfort and ease of
application.

$0.02,

dookie
(whose sworn brand is bullfrog quickgel)

"Steve Maas" > wrote in message
...
> My source is the curves in Radio Astronomy by John Krauss. Take a look
> at them; I think you'll find that the peak is fairly broad.
>
>
> Terry Morse wrote:
>
> > Steve Maas wrote:
> >
> >
> >>Solar energy is largely black-body radiation at about 5600K, which peaks
> >>at a wavelength around 1 micron, in the infrared.
> >
> >
> > You're off by a factor of two. Solar energy peaks at about 500 nm,
> > which is visible yellow/green(*). The percentage of solar energy in
> > the infrared range is rather small when compared to the visible
> > light it emits.
> >
> > * Wien's Law: peak wavelength = 2.898E-3 / T
> > --
> > terry morse Palo Alto, CA http://www.terrymorse.com/bike/
>