P3D Re: light, stricly speaking....

[Gabriel Jacob <jacob@xxxxxxxxxxxxxx>]

John R. writes:
>Heat is not *any* form of electromagnetic radiation at all! :-)
>The analogy is not useful.

Sorry, but it is! This has been one of my points all along. If you
checked those books in the libraries you would have seen terms such
as heat absorbing glass, heat reflecting mirrors, heat transmitting
mirrors, radiant heat (yes RADIANT heat!), etc....., I think you
get my point, which is, it is accepted practice to use the term
heat. 

According to your logic, invisible light is a common term, which
makes it correct. Therefore if it is a common term and accepted
practice (not true), WHY is heat absorbing glass a misnomer? It
is an accepted term in describing the above objects. If anything
it is a more common term (heat to describe IR than calling IR
invisible light) than invisible light!

>I actually went to a technical library to check this out, and looked in
>a goodly number of respected publications for the definition of "light".
>I found three definitions, typically at least two per publication:
> 1) the visible range of electromagnetic radiation, roughly 400nm to 700nm.
> 2) the range of electromagnetic radiation including infrared, visible,
>      and ultraviolet.
> 3) the entire electromagnetic spectrum.
>
>There was not any note that any of these definitions was more valid than
>the others. This is the accepted usage.

First, I didn't see any visible light or invisible light in your above
quotes. :-) Secondly, the books I'm experienced with usually give
preference to visible radiation first, which I think is what you imply
above also. 

>Earlier in the debate on the definition of "light", one poster criticized
>another for "redundancy" in the use of the term "visible light". All of the
>technical publications I checked used the term "visible light" without shame
>or apology, so I do not believe that earlier criticism was merited.

Yes it was merited because "heat absorbers" was said to be a misnomer.
I don't know which publications you looked at but the ones I've read don't
over use these kind of terms and will use such terms as visible and
invisible light rarely. They might even use it in passing but then revert
to more precise terms in the main body of the text.

>I would speculate that the common accepted use of the term "light" to
>apply to ultraviolet and IR may have much of its basis in history - these
>ranges were first detected by the use of optical equipment, and were
>perceived as continuations of the optical spectrum. It also makes some sense
>to continue the use of this terminology - UV and IR are generated and
>manipulated using techniques that are much closer to those for visible light
>than those for X-rays and microwaves.

First of all it is not accepted in all fields. As I mentioned it depends on
the field of interest. Most books will mention that UV and IR is a form of
invisible light but subsequently revert to correct terms as mentioned
before. They don't use the term invisible light for UV, IR, etc. This is
not accepted practice and leads to confusion rather than to enLIGHTenment.

>It is also more incumbent on a person wishing to make a correction to
>be careful not to use loose terminology in making the correction (e.g.
>the definition of heat, and the description of what a camera does).

I'm sorry, I really don't know how you arrived at this conclusion. I
hope the above clarifies for you that this is not the case and if
one wants to use correct terminology, to at least be consistent.
Another perfect example which you omit is the comments I made with
reference to radiant heat. If we go by the strict statment in the
report that heat is NOT IR (which I agree with!) then how does heat
radiate? Only electromagnetic radiation can radiate. For your
information all these terms, "heat" and even "radiate" can have
different meanings depending in the context. For example in different
situations, "radiate" can mean to radiate a non-electromagnetic
component. In the original context this was not the case. 

As for what a camera does, your analogy with the pin hole camera doesn't
hold water! ;-) The implication, because we can see IR with an IR
camera makes it light, makes as much sense as, since I can pick up
radio waves with my receiver, means radio waves are sound! Makes
sense? Not to me either.

P.S. A thousand apologies to Jeff!

Gabriel



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