In article <ipbbc.net>,
George Nospam <net> wrote:
You see visible light, not the infrared that CD-drives use. To the
drive, in the spectrum it can "see", the disk is probably close to 100%
opaque/reflective. To you, in a different spectrum, it looks clear.
Transparency/opacity in one region of the spectrum says nothing about
the transparency/opacity a material will exhibit in another, totally
different, region of the spectrum.
As an example, consider X-rays. A piece of plastic may very well be
absolutely opaque to visible light, but move up the spectrum a bit, into
the region occupied by X-rays, and it's as perfectly transparent as the
finest plate of glass you've ever looked through. Similarly, a piece of
lead crystal is nearly perfectly transparent in visible light, but in
the X-ray range, it's as opaque as a solid brick wall.
Exactly the same thing applies to the infrared that CD drives
produce/see. Some materials will be transparent to it, others will be
opaque, and others will be somewhere in between. Yet the materials that
are opaque to it may very well be completely transparent in visible
Don Bruder - net <--- Preferred Email - unmunged, SpamAssassinated
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