Replying to LO28279 --
Dear Organlearners
John Dicus <jdicus@ourfuture.com> writes:
>I wonder if the kind of light we need depends on
>what we're looking for. Or what we'll see depends
>on the light we use. You know -- like the light we
>use to read works well with our eyes and paper and ink...
Greetings dear John,
I like your wondering.
Should we look in the dark for a green object against a black background
with a red light, we will not see it. All will be black.
The fatal error in my mind to make, is to use a pure green light to look
for the green object. We will see the green object, but we will not see a
red object which may also be there. We have to use a light having all
colours to see all objects of whatever colour.
And we have to keep the possible paradigm shift in mind. For example, some
of the rockier deserts have semi-precious stones here and there. To post
them in daylight is difficult because they usually look like the ordinary
stones there. But in the dark, using a UV (Ultra Violet) light, it is easy
to spot many of them. The UV light self cannot be seen because the eyes
are not sensitive to it. (Actually, it is dangerous to look at such UV
light because it damages the retina. UV light has far more energy than
visible light because of its much higher frequency.)
Ordinary rocks reflect UV light as UV light. But many semi- precious
stones absorb the UV light, lowers its frequency and then emit it as
visible light. (These stones have far more order in them to do it than
ordinary rocks.) This process is called luminesence.
So, if we want to spot paradigm shifts, we will have to step up the energy
of the light we are using.
With care and best wishes
--At de Lange <amdelange@gold.up.ac.za> Snailmail: A M de Lange Gold Fields Computer Centre Faculty of Science - University of Pretoria Pretoria 0001 - Rep of South Africa
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