[Aavso-photometry] Help with light Light Box Lamps

[Wolfgang Renz]

Hi Brad

To get output in the blue at all, incandescent type lamps
have to have a color temperature of above 3000 K which
usually results in temperatures of 200° C and much more
close to the bulbs. To get a sun light like output, the color
temperature must be even above 5000 K. Everything below
that value will give a rising output towards the NIR.

Some light source types require a certain minimum surface
temperature to operate as intended (halogen, ...). So these
bulbs get usually much too hot for usage in a foam core or
even a plywood light box. Most acceptable light sources
showing a continuum without stronger emission peaks have
this issue. These might be well used for dome flats but not
for light boxes if they are not made of metal. 

Mini lamps might do the job in some cases, but must be
checked if they don't get too hot for a foam core or even
a plywood light box. I'm sure nobody of use wants to torch
their scopes (even not at christmas or New Year's Eve).

For the red/far/red/close-NIR you might also consider miniature
incandescent lamps (like e.g. for toy trains / street lights or one
step larger) and use these together with the warm-white LEDs.

If you use a warm-white white LEDs, the narrow blue peak is
about just as high as the wide green dye reemission peak.
So these behave a bit "better" photometrically in the blue
than the daylight-white or cool-white white LEDs.

Clear skies
 Wolfgang

-- 
Wolfgang Renz, Karlsruhe, Germany
Rz.BAV = WRe.vsnet = RWG.AAVSO



----- Original Message ----- 
From: "Brad Walter" <bswalter at hughes.net>
To: <aavso-photometry at mira.aavso.org>
Sent: Sunday, November 11, 2007 11:34 AM
Subject: [Aavso-photometry] Help with light Light Box Lamps


> A number of years ago I built a light box to be used for
> astrophotography using white LEDs. I know, I know, I
> know, sacrilege for photometry. My light box is the Don
> Goldman Design
> http://www.astrodon.com/oldsite/LearningCurve.html
> using the Nichia NSPW500BS LEDs.
http://www.astrodon.com/oldsite/White%20LED.gif
> Although the spectrum of these LEDs is quite blue shifted,
> they work well enough in R and V, are barely acceptable
> in B (even though the LED spectrum is shifted in that
> direction), but trying to use them for Ic flats, is a totally
> pointless endeavor (essentially no output below 700 nm).
> So I want to replace the LEDs with a 12V light source that
> has a more even spectral distribution throughout the BVRI
> range. The little bit of research I have done indicates that
> Xenon lamps would be a good choice and there are some
> 5 watt 45 lumen lamps available from
> www.unitedhalogenbulb.com
> that look like they might do the trick.
> The light box uses four mini light sources baffled to shine
> toward the back of the box, and with a suitable potentio-
> meter in series, I think these Xenon mini lamps would give me sufficient Luminous flux to do flats in any of the BVRI
> filters in 10 to 20 seconds. 
> 
> Does anyone have any experience with Xenon or other low voltage mini lamps
> for a light box?  
> 
> 
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