Which UV light source

[reinier_de_vlaam]

I'm currently using philips 40w/05 UV tubes for my palladium and

Cyanotype prints. I have several problems with these, including long

blinking times for turn on and 'long' exposures (12-16min).

 

Can anyone recommend me any alternatives. Would browning tubes do

(but these would be pretty long)?

[j king]

A good overview of UV light sources is at:

 

http://unblinkingeye.com/Articles/Light/light.html

 

I am currently using 20W UV bulbs (F20T12/BL). The bulbs are about 6"(150mm) from the print frame and my "new" cyanotype exposures are about 15 min. If the bulbs were placed closer together - they are curently on 2.5" (6.2cm) centers - they could be closer to the print while maintaining even light intensity. That would cut print times.

[reinier_de_vlaam]

thanks..I lost that link. Seems I have to get me some Philips BL's

[joseph_wisniewski]

Reinier,

 

I've got lots of advice for you, but first, I'd like to ask you a couple of silly questions.

 

What country are you from? All the part numbers I'll mention further down are for 120V (US and canada) wiring. If you're in Europe with 240V, the principles are the same, but you'll have to track down different parts.

 

Are "browning tubes" what an American would call "tanning tubes"? Are those 8 foot (2.4 meter)?

 

Did you build your UV source from the Jon Edwards plans that you see on the internet?

 

The Jon edwards plans have a serious flaw. His frame doesn't have a "ground plane", a metal plate under the tubes. This makes them harder to start, which gives you a longer "flicker" period before you get good light. That sounds like one of your problems.

 

Now, I'm guessing your 40w/05 UV tubes are the 4 foot (1.2 meter) long 40 Watt Philips "Super Actinic" tubes. They probably have an F40T12 designation on them. If memory serves, the complete number is F40T12/05.

 

The problem is probably your fixtures, not your tubes. If you're using commercial fixtures, they have "energy saving" ballasts. The Jon Edwards plans recommend the same ballasts. They "start" badly, even if you have a ground plane (they're even worse without one, though).

 

The worst thing, though, is that they "save energy" by driving regular tubes to about 60% of their rated power, so a 40w tube only gives you 24w. Which means long exposures. And, for darkroom use, they don't save energy after all, because giving you 40% less light means you need 67% longer exposures. The watt-hours come out the same, and all the photographer gets is agrevation.

 

This ratio of the ballast's "actual power" to the bulb's "rated power"

is called the "ballast factor". Be careful, there's another number called the "power factor", which actually has nothing to do with "power". A ballast can have a horrible 0.60 ballast factor, giving you aggrevating long exposures, yet still have a 0.98 power factor.

 

You can find electronic (or even some magnetic) ballasts that start better and give you ballast factors of 0.90 or even 1.04 (the highest I've seen).

 

Our 24 inch printing frame uses the very same tubes Jonathan uses, 24 inch (60cm) F20T12/BLB. Initially, I used the ballasts in Jon Edwards' plans, Advance RL-2SP20-TP ballasts. These are rather typical ballasts, easy to obtain at hardware stored, with a low 0.6 ballast factor. (Also easy to obtain are the Universal 447-LR-VLH-TC-P, with an even worse 0.55 ballast factor). We use, instead, the Advance HM-2SP20-TP, with a nice 0.9 power factor. They're harder to find, you have to hit a decent sized electrical supply store, instead of the local hardware store. They start better than the energy saving ballasts.

 

Now, my big frame, 18 bulbs, 48 (1.2 meter) 40 watt F40T12/BLB, uses a technique called "overdrive ballasts".

 

I advise you DO NOT TRY THIS. If done properly, it can drive the F40T12 with a ballast factor of 1.4-1.5, which cuts your exposure time in half compared to "stock" ballasts. If done improperly, well, it's a 1060 Watt system that uses a 600V pulse to start the ballasts. It's dangerous.

 

This is the link for the system that YOU SHOULD NOT BUILD.

 

http://forums.dpreview.com/forums/read.asp?forum=1025&message=8027113

 

Again, this is dangerous. DO NOT BUILD THIS.

 

Ciao!

 

Joe

[don_mckeith]

I use the sun-

no problems

[reinier_de_vlaam]

Thanks Joe that's usefull information. The ballasts: you probably mean the big boxes (coil/transformers?) not the starters (I don't know how they are called over there? (Difficult with these technical terms to get the right objects)

 

Indeed I use 2 2-tubes commercial frames. Should I connect there frames with a metal plate?

 

Here in the netherlands the sun is not shining that often, like scotland were known for our rain :( So I would prefer a more reliabale source.

[joseph_wisniewski]

Yes, the ballast is the large, heavy box with the transformer.

 

Wow, do they still have "pre-heat" ballasts, the kind that need starters, over there in the Netherlands? I don't think we have then in the US any more, nor do they have them in the larger EU states like the UK or France. The ballasts here all have startup control inside the ballast: trigger start, rapid start, or instant start.

 

The ones I use for the big four foot high output fixture are "instant start", just apply power and they're on. It's pretty cool. They don't even run the filaments, they just apply a high voltage pulse, and that ionizes the gas, and the bulbs start, just like a larger version of a photoflash or strobe.

 

The ones I use for the 2 foot fixtures are "rapid start". They fire the filiments, then pulse the bulbs on about 2 seconds later. A single pulse and they strike, no flicker. The filaments stay lit as long as the bulbs are on, so you can see them glowing orange at the end of the purple blacklight tubes.

 

If there's already metal frame under the bulbs, you don't need any additional metal connecting multiple fixtures. There has to be something metal under the bulb, along the entire length of the bulb, about 1cm (or less) from the bulb. The metal plate has to be grounded.

 

You can actually get good starting with a copper wire running along the length of the bulb (but not too close). I've used that technique to start bulbs that were freestanding inside long plexiglass tubes. The T-12 (1-1/2 inch) tubes were inside 2 inch ID plexiglass tubes. A wire for the operating voltage ran up one side of the inside of the tube, and a ground wire for starting ran up the other side.

 

And I don't agree with the other poster, either. Even when the sun is shining, intensify varies with time of day and season of the year. I don't want to kill expensive platinum paper tinkering with exposure, nor do I want to use an integrating exposure meter for an outdoor exposure. Seems so "wrong" to require the use of a 20th century exposure meter in order to get decent results from 19th century processes.

[reinier_de_vlaam]

I will go and ask about these balasts in my store. I bought cheap frames as I though it would all be the same anyway. Proves again, buying cheap is expensive ;-)

 

I don't like sun exposure either. It will often do, but hey..this holland, were known because of the rain...