[Aavso-photometry] Halogen lamps for flats

[Brad Walter]

Wolfgang, the box is made out of 3/16" (~8 mm) thick white foam core board.
The 120 V 20 W (330 lumens) Halogen lamps certainly are hot at the surface
of the bulb but the sides and rear of the fixture stays cool. I was still
concerned about heat build up in the box surface opposite the lens side of
the light. I have run the lamps at full voltage for 30 minutes with foam
board only 1.5" (~40 mm) from the front of the light and the heat build up
is not excessive -just slightly warm. In addition, the lights are mounted on
foam blocks that angle them at 45 degrees (compound angel) toward the closed
end of the box that actually gives about 4" clearance between the front of
the light fixture and the foam board and the foam board is angled relative
to the perpendicular from the fixture. I am going to these "bright lights"
to try to reduce my flat time from an over an hour currently (for 20 flats
each in 3 filters) to 5 minutes. I chose the halogens because they are
small, even including the fixtures compared to normal incandescent bulbs,
are more efficient (less heat per light), and have a broad spectral curve. I
will try to control the light level with a SmartHome digital dimmer so that
I can preset dimming levels for different filters, and one day if the
motivation becomes strong enough, write a script to change the dimming level
when I change filters while taking flats. If the SmartHome dimmer isn't
sufficiently consistent, then I will have to go to a Varian. They are
expensive compared to the dimmer, and very expensive if you get one equipped
with a stepper motor control.  

-----Original Message-----
From: Wolfgang Renz [mailto:wr-astro at kabelbw.de] 
Sent: Sunday, April 12, 2009 12:29 PM
To: Barbara G. Harris; Brad Walter
Cc: AAVSO-PHOTOMETRY
Subject: Re: [Aavso-photometry] Halogen lamps for flats

Hello

Just out of interest:
What are your light boxes made off ?
Foam core ? Ply wood ? Metal ?

Do the halogen and incandescent bulbs not get too hot when oper- ated at the
nominal voltage for a longer time ?

As halogen lamps need a certain pretty high temperature on the in- side of
the glas bulb to operate as intended, they might get really very hot (> 300°
C), hotter than usual incandescent bulbs (especially if these are operated
at a lower than nominal voltage). This temper- ature should be also high
enough to inflame most materials com- monly used in light boxes if the
surrounding of the bulbs is not activly cooled somehow.

If the lamps have not enough output in the NUV one might still make diffused
sky flats of a few seconds right after sun set or right before sun rise and
use the light box just for BVRcIc flats.

Clear skies
 Wolfgang

--
Wolfgang Renz, Karlsruhe, Germany



----- Original Message ----- 
From: "Barbara G. Harris"
To: "Brad Walter"; <aavso-photometry at mira.aavso.org>
Sent: Sunday, April 12, 2009 6:45 PM
Subject: Re: [Aavso-photometry] Halogen lamps for flats

> I would think that you would need to take the filter off to get U flats
(but
> I would wait for others to answer).  How many lumens will that 20 watt
> halogen lamp put out?  How many are you using?  I have a large light
> box for my 16" Meade SCT(I don't remember the exact dimensions of
> the box) but I use 4 15 watt incandescent bulbs in my light box with a
> rheostat to take all of my flats except for the I filter, then I switch
over to
> 7.5 watts.  The 15 watt bulb is 110 lumens and the 7.5 watt puts out 55
> lumens.  Usually halogen lamps are more efficient and require a lower
> wattage than an incandescent light to get the same light output.  I
usually
> shoot for 5 sec flats and adjust my light output to get a 5 min flat at
about
> 40% full well.
> 
> 
> 
> -----Original Message-----
> From: aavso-photometry-bounces at aavso.org On Behalf Of Brad Walter
> Sent: Sunday, April 12, 2009 12:10 PM
> To: aavso-photometry at mira.aavso.org
> Subject: [Aavso-photometry] Halogen lamps for flats
> 
> I am about ready to mount some 20 watt halogen lamps in a new light box.
> The fixtures include a UV filter which is required for normal household
use.
> Do I want to leave the UV filters in or take them out? My inclination is
to
> take them out since I want to use the light box for the full UBVRI
spectrum
> and the spectrum of a "halogen bulb in a desk lamp, which would normally
> have the filter in place, rolls off sharply above 500 nm as shown on the
> ledmuseum.org website.