UV Light Source - Proper spacing for screw in BL bulbs?

[Mark G MacKenzie]

I have just discovered the existence of the screw in BL fluorescent bulbs (for myself). Several earlier threads brought them to my attention.

They offer significant cost and weight savings for my soon to be built light source unit.

My questions are these:

1. What is an appropriate spacing (unit to unit, or circle of coverage to circle of coverage)?

2. What "stand off" distance should I calculate for between the tip of the bulb and any contact printing frame?

3. Are there any other design criteria I should think of when altering a light box design from standard long round cylinder tube to these new tube forms?

4. If I were to replace my Crawford UV meter for a modern one to measure light distribution, actinic component, etc. which might anyone recommend?

Regards

Mark

 

[kudzma]

Mark,
I built a UV box with 12 20W spiral fluorescent BLB bulbs (3x4) spaced 6" apart (from center of bulb) and 5" above the contact frame glass. It gives perfectly even lighting, easily covering 8x20" (my biggest format).

Linas

 

[Mark G MacKenzie]

Mark,
I built a UV box with 12 20W spiral fluorescent BLB bulbs (3x4) spaced 6" apart (from center of bulb) and 5" above the contact frame glass. It gives perfectly even lighting, easily covering 8x20" (my biggest format).

Linas

Great! A simple calculation indicates that you should be able to expose larger paper sizes and still have good peripheral lighting even though you are only doing 8 x 10 now. Was that in your mind when you designed such a large area of lighting, for future potential?

Regards

Mark

 

[Mark G MacKenzie]

OOoops. Sorry, too fast on the reply. I just noticed you said 8 x 20 inches not the 8 x 10 I thought.

Disregard my questions then, your size answers them.

Regards

Mark

 

[avandesande]

Keep in mind that the 20w bulbs cost twice as much as the 15w bulbs. What kind of exposure times are you getting with the 20 watt setup?

 

[Shinnya]

Linas,

Is there any way I could take a look at your UV box? I am thinking of making a larger one to accommodate several frames for class use. I was thinking of making with tubes, but now bulbs seems to be easier, lighter, and cost effective.

Let me know. Thank you for your time.

Warmly,
Tsuyoshi

 

[juan]

I built a box using four of the 15-watt versions of the bulbs. I installed them in standard porcelain lamp fixtures which space the bulbs about 2 1/2 inches apart. The bulbs are about 2" above the negative. The inside of the box is simply painted white.

I have been exposing negatives I made to print properly on the last version of Grade 2 Azo - print times run about 12-minutes for Vandyke browns.

I do notice some falloff on the ends of the prints, so I think I'm going to get two more bulbs - making my bank 2 bulbs wide and 3 bulbs long. I see no evidence of gap in exposure between the bulbs.

The bulbs do not all come on at exactly the same time - some are about a second slower than others, however at the printing times involved, I don't think a second makes any practical difference.

The bulbs have built in ballast, so the expense is much lower than with tubes requiring separate ballast.
juan

 

[kudzma]

Tsuyoshi,
I'll take some pictures and post them here on AGUP sometime soon. It was very simple to build and the 20W screw-in bulbs are cost effective and very easy to wire. My print times (Juan's question) are 10-30 min depening on the negatives. My Pd/Pt negs are quite dense.

My bulbs come on pretty much all at once, but keep in mind that you should warm up BLB's of any type before use. I warm them up for about 1 min before each exposure.

 

[sanking]

Over on the alt-photo-process I started a conversation about the spiral BLB tubes and several people got interested in them and built working units. With her permission I am going to share with you a personal message from Judy Rowe about her personal experiences with these tubes. Judy does not post on apug.org but has indicated she would be willing to correspond with members about her unit.

I do want to mention that the spiral tubes that work in incandescent fixtures do not reach full output immediately on being turned on, as is more or less the case with regular tubes. For that reason it is very important that you allow them to warm up being timing an exposure.

Sandy

From: judyrowetaylor@comcast.net
To: sanking@CLEMSON.EDU
Subject: Re: FW: Re: update: screw-in BLB light-box
Date: Mon, 19 Dec 2005 02:31:02 +0000
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Hi Sandy,

I am currently taking a break from the alt-photo email list, but thought you might be interested in this update. I have changed from the 13 watt screw-in fluorescent bulbs to 20 watt ones and this has cut my exposure time for PT/PD (75% palladium + 25% platinum) to 7 minutes for "max black." These bulbs, from buylighting.com, are actually physically a bit more robust that the 13 watt ones. I am still on 6" centers since that was the configuration of the light fixtures I used in constructing the box. Distance from tip of the fluorsecent tube coil to contact frame plane (glass surface) is approximately 4 inches.

I am using a digineg step tablet, Clay Harmon's method for the 2200 (green D=1.9) and, with a few more iterations, should have the curve perfected. So far I have only tested Pt/Pd with the new bulbs.

I expect if I were to redesign the box and install 8 individual ceramic sockets (or even 10) - instead of the two panels of three sockets each (6 bulbs) - I might need only 4 or 3 minute exposures. Though once I move to larger than 8x10 prints I will probably just make (or purchase) a lightbox with standard tubes rather than making a larger box with screw-in bulbs. It will be interesting to see what the actual life-time of these screw-in bulbs will be for contact printing, if I remember to track the usage minutes.

Happy Holidays,
Judy

 

[Shinnya]

Sandy,

Thank you for posting Judy's message. I have one question:

What would be the reason why she would use tubes when she moves to anything larger than 8x10?

I am trying to build a larger one than currently I have (22x24" with 14 tubes) in order to accommodate many frames at the same time. My thought was that it would be cost effective, easier to build (less materials), and lighter.

As for other details, a use of 20w bulbs and 6" OC seem to work fine...

Any thought on this? Thank you for your time.

Warmly,
Tsuyoshi

 

[sanking]

I don't know the reason why she would want to go to regular tubes for larger than 8X10. It seems to me that a larger unit built with the spiral tubes should be just as effective as a small one, at least in terms of weight and cost.

However, if I were to build a unit with the spiral tubes I would probably plan to space them closer than on 6" center. The more radiation you get over a given area the faster your printing times, and I calculate that if you were to space at 3.5" on center the unit would be more effective than one built with regular tubes.


Sandy

Sandy,

Thank you for posting Judy's message. I have one question:

What would be the reason why she would use tubes when she moves to anything larger than 8x10?

I am trying to build a larger one than currently I have (22x24" with 14 tubes) in order to accommodate many frames at the same time. My thought was that it would be cost effective, easier to build (less materials), and lighter.

As for other details, a use of 20w bulbs and 6" OC seem to work fine...

Any thought on this? Thank you for your time.

Warmly,
Tsuyoshi

 

[avandesande]

Probably the only advantage of the spiral bulbs would be a higher energy density as Sandy suggested. One bad thing about the spiral bulbs is the ballast will be in your box. With normal bulbs you can put the ballast somewhere else so there will be less heat.

 

[sanking]

I am not sure how these spiral tubes work, but there does not appear to be any ballast as they screw directly into regular household sockets. And so far as I can see they do not seem to produce more heat than tubes, though I would certainly recommend the use of a fan with both the spiral and regular tubes.

Sandy

Probably the only advantage of the spiral bulbs would be a higher energy density as Sandy suggested. One bad thing about the spiral bulbs is the ballast will be in your box. With normal bulbs you can put the ballast somewhere else so there will be less heat.

 

[avandesande]

The ballast is in the socket. It doesn't use a coil but some sort of thyrisistor to limit the current. I have seen this on little HPS units. They do make heat though.

 

[Jim Noel]

I believe the electronic ballast is in the base of each bulb. This base does get warm, but, in my experience, not hot. I believe a large muffin fan would keep a bank of these cool enough to prevent adversely effecting exposure times.
Jim

 

[avandesande]

It probably isn't an issue then if you need to use fans in either case.

 

[Poptart]

So y'all are using compact black light florescents to make a light table? Interesting. I tried black light--incandescent & florescent bulbs & tubes--to print gum. Nothing gave me any exposure. I finally bought an old GE sunlamp. Works great. (The instructor of the class had offhandedly dismissed it when I'd suggested one.) I just tip a fan toward the surface of the contact printing frame while the exposure is underway and for cool-off afterwards. Of course it's a hit-or-miss propisition finding one, but I've since bought a new old stock replacement bulb too.

 

[sanking]

The incandescent Black Light bulbs put out very little if any UV radiation so they are essentially useless for UV sensitive processes. The spiral BLB tubes, on the other hand, appear to put out as much UV radiation as a regular tube of the same wattage. Not sure why you were not able to print gum with BLB tubes as this process is highly sensitve to UV radation at about 350 nm, which is where BL and BLB tubes peak.

Sandy

So y'all are using compact black light florescents to make a light table? Interesting. I tried black light--incandescent & florescent bulbs & tubes--to print gum. Nothing gave me any exposure. I finally bought an old GE sunlamp. Works great. (The instructor of the class had offhandedly dismissed it when I'd suggested one.) I just tip a fan toward the surface of the contact printing frame while the exposure is underway and for cool-off afterwards. Of course it's a hit-or-miss propisition finding one, but I've since bought a new old stock replacement bulb too.

 

[Poptart]

I've heard that most alt printers today use the sodium-vapor lamps you can buy at hardware stores. I haven't tried one--that was next on the list if the sunlamp didn't work.

 

[sanking]

That is news to me. I don't know of anyone using a sodium vapor lamp for printing with alternative processes.

Anyone here have experience using one?

Sandy

I've heard that most alt printers today use the sodium-vapor lamps you can buy at hardware stores. I haven't tried one--that was next on the list if the sunlamp didn't work.