[Aavso-photometry] Halogen lamps for flats

[Wolfgang Renz]

Hi

Thx for your replys.

Good to hear that you haven't set your scopes on fire yet.

With halogen bulbs it can get tricky. Some of them have a special
heat reflecting front glas to protect the target they are aiming at (e.g.
for art illumination or desk lamps). If they have, they do emit all the
heat to the sides which then can cause a heat accumulation if they
are mounted in a slot in a lightbox without freely circulating air to
cool the slot walls.

Some of the halogen bulbs might also loose significant life time if
they are operated at a lower than nominal voltage because they
then might not reach the required temperature at the inside glass
surface to start the halogen process that brings the tungsten on the
glass surface back to the filament. In this case the glass should start
to look smoky and get darker and darker before the filament some-
when ends up in smoke.

Clear skies
 Wolfgang

-- 
Wolfgang Renz, Karlsruhe, Germany



----- Original Message ----- 
From: "Brad Walter"
To: "Wolfgang Renz"; "Barbara G. Harris"; <aavso-photometry at mira.aavso.org>
Sent: Sunday, April 12, 2009 8:16 PM
Subject: Re: [Aavso-photometry] Halogen lamps for flats

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 com-
pared 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 ta-
king 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
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.