Homemade UV box - What color lining??

rmann · Jul 14, 2009

I am making a plywood box to hold a series of UV lights - what color should the interior be? White paint, or should I use aluminum flashing? Or does it matter?

Thanks -

cowanw · Jul 14, 2009

Interesting Question.
Cabalas makes uv reflective fish lures using "UV Technology" and it seems clear that the reflection of visible light has not much to do with UV relection.
On the other hand I would be worried about a glare of reflection from flashing.
After 14 pages of google I have no better idea than a flat surface to promote a diffuse reflaction.

jeffreyg · Jul 14, 2009

I have a uv light box that was made from plywood and coated with white on the interior. I've used it for years to print platinum/palladium with no problems. The clearance between the bulbs and the printing frame is approximately three inches. It is ventilated and has a fan.
jeffreyg

Dan Dozer · Jul 15, 2009

Assuming that you are using the UV light for something like platinum printing - I'm not an engineer or anyone who is an expert on UV light, but from what I've been told, UV light that your images are sensitive to does not go around corners or reflect off surfaces - it has to be direct exposure. Case in point - when you stand in the shade out doors, is it possible to get sun burned from the sun reflecting off other surfaces? Given that, it shouldn't matter what the interior of your light box is. If you use a white or reflective surface coating, it may look brighter to your eye, but your image may not be sensitive to that extra light (different wavelength). Maybe there are some more experienced people here who can either confirm my understanding or correct it with more accurate information.

Ian Leake · Jul 15, 2009

I must admit that when I built my UV lightbox I was feeling lazy and just left the inside as plain wood. It's always worked

keithwms · Jul 15, 2009

Do *not* use bare metals, they have very high reflectance into the UV. A black matte surface is likely the best choice, but.. just about anything would be better than bare metal.

JBrunner · Jul 15, 2009

Dan Dozer said:
Assuming that you are using the UV light for something like platinum printing - I'm not an engineer or anyone who is an expert on UV light, but from what I've been told, UV light that your images are sensitive to does not go around corners or reflect off surfaces - it has to be direct exposure. Case in point - when you stand in the shade out doors, is it possible to get sun burned from the sun reflecting off other surfaces? Given that, it shouldn't matter what the interior of your light box is. If you use a white or reflective surface coating, it may look brighter to your eye, but your image may not be sensitive to that extra light (different wavelength). Maybe there are some more experienced people here who can either confirm my understanding or correct it with more accurate information.

UV absolutely does reflect, as anyone who has been on the Salt Flats out here in shorts but no underwear can attest. My NuArc has a metal reflector, but the unit is a 1k point source and precisely (more or less) designed. For a diffuse source box like you are building I don't think it will make a lot of difference. If you insist, flat white or flat silver might get you a little more energy to the print from bounce as a possible minor exposure enhancer. I highly doubt there is enough energy from any one point to cause trouble with a reflection.

photomc · Jul 15, 2009

Take a look at the the ones from Edwards Engineered Products, at the bottom of the page you will see a photo of one with the door open - the inside is white. From what I recall when I built mine, the general thoughts from what I could find then was paint it white - I used a flat white. As has been mentioned, you want the direct UV, not reflected anyhow.

Edit:Mr Brunner has a better explaniation...

rmann · Jul 15, 2009

Thanks for the information - I painted the outside white to match the cabinets it will fit into, so I will paint the inside white also.

UV absolutely does reflect, as anyone who has been on the Salt Flats out here in shorts but no underwear can attest. - I am trying to picture this - (no, maybe I better not) - but, I have to ask - did it (or they) peel??

Loris Medici · Jul 16, 2009

(As you probably already know) Best UV reflector is Aluminum. You'll gain some speed if you line inside the box with aluminum panels...

keithwms · Jul 16, 2009

Loris Medici said:
(As you probably already know) Best UV reflector is Aluminum. You'll gain some speed if you line inside the box with aluminum panels...

Well, the reason why I cautioned against bare metal is that the reflections can be irregular. If you take the time to make a really good half cylinder or something, then yes, maybe it's a good idea, but otherwise I think the reflected light will be uneven.

Of course, if the reflective surface is a long way away, then ... inverse square law... it won't matter.

Loris Medici · Jul 16, 2009

I think one would get better coverage and more even light with aluminum panels on top and sides (including the front cover)... That would prove very useful especially with large (close to the max. printable area) prints. Reflected light will not be stronger than what you get at the very center, right below the bulbs, so the possibility of exposure getting more uneven is out of concern. You'll get just more light (that won't exceed the max. that you get in the center) on the edges and corners, and that's compared to usual setup -> you don't have the risk to overexpose the edges/corners. (Even if it was that way, then there's the fact that more exposure at the corners is much better than less exposure. We tend to burn the corners in S/G printing right?)

Regards,
Loris.

Ian Leake · Jul 16, 2009

I expect that the type of light source has a bigger impact than the interior coating. If you have a bank of UV tubes then you've got yourself a very soft light source - so soft that interior reflections, fall-off, etc are not worth worrying about. If you've got one or more UV bulbs then you've got one or more hard light sources - reflections, fall-off, etc may then be worth worrying about. Choice of hard light or soft light will also have an effect on your contact print, but that's for another thread

Ian Leake · Jul 16, 2009

And another thing... How much time is one internal coating over another actually going to save? My standard starting point for one paper is 3 minutes, and 6 minutes for another. If coating the interior with a super-special coating reduced my printing time by a stop (which is highly unlikely - perhaps 1/3 of a stop is more realistic), then that would save between 90 and 180 seconds. Compare that with the end to end processing time of a print, which for me is about 45 minutes before it goes in the wash: that's a saving of about 5%. My maths isn't up to working out what a 1/3 of a stop saving would save, but obviously it would be quite a bit less.

So, if painting the interior white or lining it with aluminium makes you feel better then go ahead and do it. But don't think that it's going to save you any significant amount of time or increase print quality. If you want faster exposure then buy more lights. And if you want more even coverage then buy UV tubes which are longer than your biggest printing size and pack them close together.

Nicholas Lindan · Jul 16, 2009

It depends on what you are exposing and what you are exposing it with.

If it is relatively insensitive to / or the source produces little light at wavelengths shorter than 440nm then white house paint is an excellent choice, better if you add about 50% barium sulfate.

If shorter than 440nm then aluminum may be a better choice.

If you are using aluminum it has to be aluminum that has been polished and coated for UV reflector purposes. You want a textured or dimpled surface, not a mirror finish. Google will turn up several manufactures.

Aluminum foil is probably the most dismal choice there is.

donbga · Jul 18, 2009

keithwms said:
Well, the reason why I cautioned against bare metal is that the reflections can be irregular. If you take the time to make a really good half cylinder or something, then yes, maybe it's a good idea, but otherwise I think the reflected light will be uneven.

Of course, if the reflective surface is a long way away, then ... inverse square law... it won't matter.

Keith,

This is just pure drivel ....

Don Bryant

keithwms · Jul 18, 2009

Homemade UV box - What color lining??

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