Re: filmscanners: Re: looking at the Sun

["Alan Tyson" <AlanTyson@bknowl.freeserve.co.uk>]

UV is dangerous through breaking chemical bonds directly; IR
is dangerous through cooking (breaking chemical bonds by
heating as in a grill or a toaster).  The sun's radiant
energy has lots and lots of both. Your retinal heat
receptors (if any) won't be quick enough to prevent damage
if you put a small solar image on your retina for long.

If IR was nothing to worry about, fogged colour neg film
would be fine for eclipse viewing, and it isn't, (see
attached spectra from NASA's website).

The 'greenhouse effect' with respect to the Earth is
unfortunately misleading with respect to greenhouses. It's
because the incident black body radiation from the sun is
characteristic of intense 6500K and the reradiated energy is
characteristic of weak 300-odd K. Not a lot of the sun's UV
gets to the surface because it's absorbed in the ozone
layer, but the energy does stay in the atmosphere and warm
us up indirectly. The function of greenhouse glass and solar
water heater coverings is to let IR in and keep draughts
out.

This is another divergent OT discussion, so I'm sorry for
prolonging it, but it is a safety issue. When I can find an
absorption spectrum of optical glass I'll send it you
privately. Your greenhouse protects you surprisingly well
from UV in temperate latitudes, as I recall (but not well
enough for hanging up pictures of the plants).

Regards,

Alan T

----- Original Message -----
From: Frank Paris <marshalt@spiritone.com>
To: <filmscanners@halftone.co.uk>
Sent: Sunday, February 04, 2001 10:13 PM
Subject: RE: filmscanners: Re: looking at the Sun


> Infra-red is on the other end of the light spectrum and is
of very low
> energy per photon compared even to light. It is manifested
to us as heat.
> How is this dangerous?

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