sunscreen makes you hotter?

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.

BaCardi said:

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.

BaCardi <[email hidden]> wrote in message news:<[email hidden]>...

Quoted message said:

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.

Common sense, good concept.

One thing that was missed in a lot of this discussion is the difference between UV absorbed by the
skin and UV absorbed or reflected by sunscreen *on* the skin. Sunscreen is only on the surface of
the skin. Ergo, the body is not being heated by the UV other than the very surface of the skin where
airflow removes the heat instead of your body's cooling system.

My experience is that judicious use of a non-oily sunscreen helps me to feel less hot in direct
sunlight, especially my ears, neck and face which can get hot to the point of a distinct burning
sensation. A high spf sunscreen seems to relieve that. I also use it on the tops of my arms and
hands but don't bother otherwise. Test it on your ears on a sunny day. I think you will notice the
difference.

Common sense would be to use sunscreen in a way that maximizes the amount of UV energy blocked
from entering your body at its most vulnerable areas while minimizing the effect on your body's
cooling system.

JP

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

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 <[email hidden]> wrote in message
news:<[email hidden]>...

Quoted message said:

Joe Riel may have said:

Werehatrack <[email hidden]> writes:

Quoted message said:

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.

BaCardi <[email hidden]> wrote in message news:<[email hidden]>...

Quoted message said:

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.

"BaCardi" <[email hidden]> wrote in message "]news:[email hidden]...

Quoted message said:

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

Tim McNamara said:

In article <eMdWa.33166$Ne.31813@fed1read03>,

Bill Davidson said:

Bob Denton said:

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.

Werehatrack said:

Tim McNamara may have said:

In article <eMdWa.33166$Ne.31813@fed1read03>,

Bill Davidson said:

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.

Quoted message said:

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.

Quoted message said:

Quoted message said:

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.

Quoted message said:

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.

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 said:

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.)

Steve Maas said:

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 terrymorse.combikeOpen ↗

"Steve Maas" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

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?

Quoted message said:

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 said:

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.)

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 said:

Steve Maas said:

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 terrymorse.combikeOpen ↗

Steve Maas said:

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 terrymorse.combikeOpen ↗

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" <[email hidden]> wrote in message
"]news:[email hidden]...

Quoted message said:

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 said:

Steve Maas said:

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 terrymorse.combikeOpen ↗