Re: Fwd: CIR questions

["Anthony W. Maw" <amaw@xxxxxxxxx>]

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Flourescent lights work by discharging an electric arc through mercury
vapour ( inside every flourescent tube is a high vacuum and a small drop of
mercury).  The mercury vapour arc produces primarily ultraviolet radiation
(not sure whether UVA or UVB or both in what proportions) and also some
narrow line output in the green spectrum.  (that's why flourescent tubes are
primarily green when photographed with daylight film and also some street
lamps look green because they are mercury vapour arcs).  The tubes can be
made more pleasant looking (warm white, cool white, daylight) through the
use of flourscent phosphors coated on the inside of the tubes.  These
phosphors emit light in the red, green, and blue spectrums and the total
colour of the tube can be altered by changing the ratio of the colour
phosphors.  (Note that even daylight tubes only approximate 90 percent of
the actual spectrum of sunlight.)

Thus it is correct that flourescent illumination is virtually useless for
infrared photography unless you want to expose using the UVemissions only to
which the film is sensitive (but so is every other film),.

Hope this helps.

Jason Revell (in5) wrote:

> Well I don't know if you are using Colour or B+W BUT
> fluorescent lighting gives off very little IR light.  Are they just
> fluorescent lights though or are there some halogen lights as
> well as they give off a reasonable amount of IR light which would
> definitely help the exposure.
>
> I would expect (but I have never done this) that it will depend
> on the filter you are using, as there will be effectively no IR light
> above
> about 750nm so if you want to try this I would suggest using a Red
> filter
> rather than any of the 'black' IR filters.
>
> This will of course be different for EIR but I would be expecting little
> magenta in the slides.
>
> To try this out should I take my hand IR viewer to the supermarket
> next time I am going ! ?
>
> Not much help I know but let us know what happens.
>
> Jason Revell
>  ----------
> From: Spearmint
> To: Infra Red
> Subject: Fwd: CIR questions
> Date: Wednesday, 14 January, 1998 7:33
>
> Any suggestions ???
>
> Thanks in advance :)
> Gavin
>
>  ---------------- Begin Forwarded Message ----------------
> Date:        13/01  6:44 pm
> Received:    13/01  7:59 pm
> To:          Spearmint, minty@xxxxxxxxxxxxxxxxxxx
>
> hi, i've never shot infrared before and i was just wondering what if any
> effect would be produced under flourescent lighting (i have an idea that
> involves the aisle of a large supermarket). anyway, i was just
> wondering. thanks.
> jeff
>
>  ----------------- End Forwarded Message -----------------
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End of Infrared-Digest V0 #344
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