Re: Back to the IR light source concept...
From: Chris Hodges (chrisjhodges_at_yahoo.com)
Date: 08/11/04
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Date: 11 Aug 2004 07:32:05 -0700
Don Bruder <dakidd@sonic.net> wrote in message news:<un9Sc.6756$54.105069@typhoon.sonic.net>...
> In article <d36a713e.0408100613.15b7ba92@posting.google.com>,
> chrisjhodges@yahoo.com (Chris Hodges) wrote:
>
> > Don Bruder <dakidd@sonic.net> wrote in message
> > news:<LsPRc.6561$54.101665@typhoon.sonic.net>...
> > > I don't see an underdriven filament putting off a larger *ABSOLUTE*
> > > quantity of IR - Rather, I see the relationship between mount of IR and
> > > visible output changing - As in the IR output stays (nearly) the same
> > > regardless of voltage, but the visible component falls off with the
> > > voltage drop until the point where visible output is nearly nil, but the
> > > IR output is just as strong as ever.
> >
> > I'll try and model this and get back to you - but if it's battery
> > driven (i.e. if you really want to use the maglite) it will improve
> > battery life.
>
> Well, the whole point of this concept is a portable unit, so battery
> power is probably the only reasonable way I can go. Nothing says it
> *HAS* to be a maglight - that was just my "proof of concept" whack at
> the problem - but it probably will have to be battery powered to make it
> practical/portable.
I modelled the blackbody curves in excel, and you're right, by quite a
margin - I don't know whether the power requirement or the IR output
would fall faster for a given emitter as you drop the temperature
(assuming temperature control for convenience) so it might not even
save battery life.
The maglite could be a good way to go - the focussing output would
seem to help, even if you have a diffuser effect from the vis blocking
filter.
Did you ever try multiple visible gel filters - these tend to be cheap
(I seem to remember £10 (~$18)/sq foot), and for a maglite even
offcuts would be enough, so even cheaper if you have a friendly
theatrical/DJ supplies shop that does stage lighting.
e.g. Lee filters (www.leefilters.com) "Blood red 789" transmits only
1% visible in the far red, combine with (e.g.) "Bray blue 722" should
do it. I found my old swatch book recently (since the last thread) so
I can have a look with a lamp and digital camera later. With anything
less than hundreds of watts they'll last forever.
Chris
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