[mythtv-users] [Slightly OT] solar power for all our gadgets

raphy rpooser at gmail.com
Fri Mar 20 22:02:13 UTC 2009

On Fri, Mar 20, 2009 at 4:06 PM, Simon Hobson <linux at thehobsons.co.uk> wrote:
> raphy wrote:
>>  > That's the crux of it. If the heating is electric then there is ZERO
>>>  difference in efficiency - both the electric heating and light bulb are
>>> 100%
>>>  efficient at turning incoming electricity into heat. For other forms of
>>>  heating there will be some saving - but I don't know what it will be
>>> other
>>>  than "nothing like 80%".
>> This is utterly wrong. I don't need to mention anything more than the
>> fact that your electric heater doesn't emit nearly as much or even the
>> same wavelengths of visible light that your light bulb does to debunk
>> that one.
> Thank you for proving the point ! Lets not allow facts to get in the way of
> prejudice.
> So, I'm sat at home, and I've just pulled the curtains closed (which I have
> actually, it's going dark). Say I have a light bulb consuming 100W of
> electricity - and directly emitting 90W of heat. It's therefore also
> emitting 10W as visible light.
> Without ignoring the laws of physics, and in particular the law of
> conservation of energy, could you please explain where that 10W goes to if
> it doesn't heat up the room ?

I find it funny that you think light transmits heat to the air as
effectively as air convection through the the heating elements in your
electric heater. You must think we should just stop putting fans of
any type in electric heaters, then, and convert them all to visible
light sources.

More seriously, the visible light from your light bulb does not heat
the air. As a matter of fact, the air is transparent to the light
coming out of your bulb. It passes straight through the air and
reflects off of the various things in the room. That is how you see,
things, you see. The light sometimes bounces into your eyes, where it
is absorbed... your eyes it don't heat when you look at things, by the
way. Eventually the visible light in the room will be absorbed in
various objects that absorb at various frequencies. I know this is the
part where you would like to say that heating is now occurring.
However, the energy transferred to the curtains, walls, etc. can cause
different modes of excitation; not all of them will end up as phonons
which can then transfer heat back into the air. Most of the photons
will simply be scattered into the wall. Also, transferring any heat
from the walls back to the air is going to be fairly inefficient. We
don't simply heat our walls when we want to heat our houses, you know.
In fact, even though your curtains are closed, some of that heat may
actually radiate through the walls into the giant cold reservoir
outside. For that reason I can guarantee you, beyond a shadow of a
doubt, there is no way you will ever be able to transfer 100% of the
energy from a light bulb or electric heater into heat for your room. I
good bit of yes. 100%, no.

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