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The reason why phthalocyanine dye cannot be used in DVD-Rs is that the
wavelength of the laser used to burn DVDs is smaller than that used for
CD-Rs, and the dye doesn't respond to (absorb) this wavelength.

-----Original Message-----
From: Richard L. Hess [mailto:[log in to unmask]] 
Sent: Saturday, March 25, 2006 5:59 PM
Subject: Re: Further thoughts on the new CLIR report. DVDs


At 08:45 PM 3/25/2006, steven c wrote:

>Question for the technically knowledgeable...
>
>Since CD's and DVD's are (AFAIK) more or less the "same animal" and 
>operate by pressing (or "burning") pits into the surface of a plastic 
>disc, why should there be any difference in the lifespan of the two?
>
>Do the littler "holes" fill themselves up more rapidly?

There is one major difference in construction. The CD has the 
delicate top layer that is the reflective layer covered with lacquer.

The DVD's reflective layer is in the middle and the two discs are 
bonded together. That bond is a source of concern.

The CD-Rs that seem to fare best in tests use phthalocyanine dye. I 
think Joe Iraci pointed out that the DVDs do not use that dye. That 
could contribute to the lower life expectancy.

I don't know why phthalocyanine dye cannot be used in DVD-Rs, but 
apparently it cannot. The gold DVD-Rs from MAM-A, by the way, are 
only 4x while almost everyone is shipping silver 8x and perhaps faster.

Cheers,

Richard


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