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? It is only when you get into microwaves on the wide
end of the spectrum that electromagnetic radiation becomes dangerous. Since
infra-red is manifested as heat, our heat receptors will protect us long
before any damage is done, unless of course we are caught in a fire. The
reason a greenhouse builds up heat is that the light coming in is absorbed
by surfaces and then re-radiated as infrared, which can't get out. It is not
dangerous to spend all day in a greenhouse, tending your plants.
> -----Original Message-----
> From: firstname.lastname@example.org
> [mailto:email@example.com]On Behalf Of Alan Tyson
> Sent: Sunday, February 04, 2001 11:53 AM
> To: firstname.lastname@example.org
> Subject: Re: filmscanners: Re: looking at the Sun
> Infrared is also a serious, if not worse, hazard. Glass is
> fairly transparent to it, as shown by greenhouses, passive
> solar panels, the burning of holes with magnifying glasses,
> and the feasibility of IR photography with ordinary lenses.
> Most glasses absorb UV much more strongly than IR. Most of
> the materials used for sun viewing and photography (eclipse
> goggles) have a (log10) density of 5-8 for UV and visible,
> and less than 5 for IR.
> The worst of the lot is fogged colour negative film, which
> is fine in the UV & visible, but lethal to eyes because it's
> transparent to IR.
> NASA's web site has lots on this under solar eclipses.
> Alan T