[TheForge] Re: Subject: Didymium? I say "no way."

[Chuck Robinson]

Mike,
What is your take on the gold vacuum deposition/didymium filters? they seem 
far more effective than any thing else I have used.
Chuck
----- Original Message ----- 
From: "Mike Porter" <michael.a.porter at comcast.net>
To: "Sponsored by ABANA" <theforge at mailman.qth.net>
Sent: Friday, February 10, 2006 12:52 AM
Subject: Re: [TheForge] Re: Subject: Didymium? I say "no way."


> Pupil? I meant to say iris.
> Mike P.
> ----- Original Message ----- 
> From: "Mike Porter" <michael.a.porter at comcast.net>
> To: "Sponsored by ABANA" <theforge at mailman.qth.net>
> Sent: Thursday, February 09, 2006 8:53 PM
> Subject: Re: [TheForge] Re: Subject: Didymium? I say "no way."
>
>
>> Bruce,
>> Any light in sufficient amounts will burn your eyes. It is true that the 
>> smaller the wave lengths, the greater the amount of energy they carry. 
>> This is why UV is more harmful than IR. However, they both have the same 
>> main hazard--they are invisible. You don't react to either UV or IR. 
>> There is no pupil contraction to either one of them, no blink reflex, no 
>> urge to look away, as there is with too much visible light. This has 
>> every bit as much to do with  physical impact as the square of the 
>> distance.
>>
>> Also, only far range IR is felt as heat. Near range IR is not felt at 
>> all, just as green light isn't felt. So, if it packs so little energy 
>> compared to every other light band, what is the big deal? That there is 
>> so very much of it whenever anything is heated past 1000 degrees. The 
>> amount of energy that super heated objects put out as IR is huge before 
>> you ever see the faintest glow of visible incandescence. As they brighten 
>> into the visible range, the IR multiplies as well.
>>
>> Lots of people can't just look away from the heat source. How do you 
>> braze or gas weld without looking at the heat source? How do you pound 
>> incandescent hot iron without looking at it? I'm not saying everyone 
>> should rush out and get protection from IR. That's your individual 
>> choice. I was originally answering a question asked by someone who does 
>> want that protection.
>> Mike P.
>> ----- Original Message ----- 
>> From: "Bruce Freeman" <freemab222 at yahoo.com>
>> To: "theforge" <theforge at mailman.qth.net>
>> Sent: Thursday, February 09, 2006 6:45 PM
>> Subject: [TheForge] Re: Subject: Didymium? I say "no way."
>>
>>
>>> Unlike Mike, I have NOT intensely researched
>>> protective eyewear.  However, I have one pedantic
>>> correction to his posting, and one genearl issue.
>>>
>>> The pedantic correction is that the yellow "sodium
>>> flare" has nothing to do with soda reacting with air.
>>> Merely heating sodium to flame temperature is
>>> sufficient to produce the flare.  Okay - who cares!?
>>>
>>> The other observation is what I consider an excessive
>>> concern about IR radiation.  IR is translated to heat
>>> when it encounters anything that absorbs it.   If that
>>> thing then gets warm, it will retransmit IR.  Ordinary
>>> glass absorbs most IR, and many plastics do as well.
>>> You can tell if a lens absorbs IR:  place it in front
>>> of a heater and see if it gets hot.  Unfortunately,
>>> that will not tell you what wavelengths it absorbs,
>>> should that matter.
>>>
>>> The thing about IR is that it is the least likely
>>> radiation to get you in trouble -- because you can
>>> feel it.  If you're so "manly" that you refuse to look
>>> away from the fire as your face cooks, then your
>>> eyeballs will cook along with your face.  Remember the
>>> reverse-square law:  Twice the distance from the heat
>>> is 1/4 the heat intensity.  Pretty easy to avoid too
>>> much IR.
>>>
>>> None of this is to say that IR should be ignored.
>>> But, finding a clear material that would PASS IR has
>>> been a significant problem in science.  Ordinary salt
>>> (NaCl) works, as do the chemically -related salts,
>>> such as potassium bromide (KBr).  Even those start
>>> absorbing if they pick up water, so they have to be
>>> kept dry.
>>>
>>> Bottom line:  Don't be stupid and try to cook your
>>> face and eyeballs, and you'll probably have no problem
>>> with IR.
>>>
>>> UV is another ball of wax.  Never look at an arc, even
>>> briefly.  Even the reflection of an arc can be
>>> damaging.
>>>
>>> Bruce
>>> NJ
>>>
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>>
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