[Aavso-photometry] Halogen lamps

Tue Apr 14 07:59:10 EDT 2009

Hi Guys,
just needed to add a bit.
As it is even a little more tricky than stated.
Wolfgang is correct with the lower temperature affecting the Tungstan/ 
halogen recycling process,

however all is not lost.

In the Theatre and Rock & Roll lighting world, the norm is that atleast 10 
percent of the 'on time' of the halogen lamp should be at a suffient 
temperature for the  cycle to work, so typ every hour, the lamps should be 
run at full power for about 6 min.

The real issue for lower voltage is that the lamps' operating temperature 
and oviously its' spectral color will change a lot.

A good source of background info is usually the manufacturer for example, 
see http://www.gelighting.com/eu/resources/firstlight/module08/5.html

The glass covers over the front of the lamps used in Art exhibitions are 
designed to remove the UV emitted by the lamps as it is the UV radiation 
that damages the pigments in the paint, just as the UV damages and changes 
the pigments in your skin.

Some Halogen lamps have a dichroic coating on the rear (on the reflector 
side) that reflects visible light back out the front of the lamp (where we 
want it ) and passes Ir (the heat) out the back,   see fig 8.12 in the above 
manual, so these lamps may need different housings to others.

Some halogen lamps actually reflect the IR radiation back onto the filiment 
as it improves the overall effiency see fig 8.8 in the above manual

Note that some halogen lamps are sensitive to the burn position as well.

The only way to keep the color temperature constant and vary the brightness 
is either use less bulbs, lower wattage bulbs, move the bulbs further away 
(Inverse square law) or use mechanical dimming solutions.

Read some of 
http://www.gelighting.com/na/business_lighting/faqs/halogen.htm as well to 
get a further understanding of halogen lamps...
and 
http://www.gelighting.com/na/business_lighting/education_resources/learn_about_light/distribution_curves.htm 
give a good idea about spectral distribution within different lamp series.

please not that I'm not suggesting GE lamps, it's just their website offers 
appropiate reading material for the current discussion.

You really should investigate the best lamp for your needs.

Hope this helps (?)

Cheers
Blair Lade
Instrument Officer
Astronomical Society of South Australia
www.assa.org.au

----- Original Message ----- 
From: <aavso-photometry-request at aavso.org>
To: <aavso-photometry at mira.aavso.org>
Sent: Tuesday, April 14, 2009 1:30 AM
Subject: Aavso-photometry Digest, Vol 63, Issue 5

> Send Aavso-photometry mailing list submissions to
> aavso-photometry at mira.aavso.org
>
> To subscribe or unsubscribe via the World Wide Web, visit
> http://www.aavso.org/mailman/listinfo/aavso-photometry
> or, via email, send a message with subject or body 'help' to
> aavso-photometry-request at mira.aavso.org
>
> You can reach the person managing the list at
> aavso-photometry-owner at mira.aavso.org
>
> When replying, please edit your Subject line so it is more specific
> than "Re: Contents of Aavso-photometry digest..."
>
>
> Today's Topics:
>
>   1. Re: Halogen lamps for flats (Wolfgang Renz)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Mon, 13 Apr 2009 00:15:02 +0200
> From: "Wolfgang Renz" <wr-astro at kabelbw.de>
> Subject: Re: [Aavso-photometry] Halogen lamps for flats
> To: "Brad Walter" <bswalter at hughes.net>, "Barbara G."
> <barbharris1 at hughes.net>
> Cc: AAVSO-PHOTOMETRY <aavso-photometry at mira.aavso.org>
> Message-ID: <F43B22F2116B41D5AEB942B43A803492 at WINXPPROWR>
> Content-Type: text/plain; charset="iso-8859-1"
>
> 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.
>
>
> ------------------------------
>
> _______________________________________________
> Aavso-photometry mailing list
> Aavso-photometry at mira.aavso.org
> To change options or unsubscribe, goto 
> http://www.aavso.org/mailman/listinfo/aavso-photometry
>
> End of Aavso-photometry Digest, Vol 63, Issue 5
> *********************************************** 