Anyone Use LED lights for a contact printing box

[John Dean]

Hello, I am going to be building a contact printing box to expose OHP negatives for Platinum/Palladium and Gum printing, as well as some silver contact printing.

Is anyone using LED lights in such a lightbox and if so can you comment on how the compare to uv fluorecet in regard to fluorescents in terms of exposure time. Also since there are so many types of led lights on the market, which work best for this sort of application?

Any help would be appreciated.

John

 

[jvo]

i, too, was hoping for a response... guess we got an answer by omission!

 

[John Dean]

Yea, very strange indeed that the specialists haven't moved in this direction. Certainly they are powerful enough, they are cheap, last a long time, and they use less electricity. But the main reason I'm building a box for them is how light and small they are. I can build a 30x40 printing box that is very lightweight and takes very little space. They are being used for some expensive big commercial silk screen systems.

john

 

[TheMissingLink]

Hi,

I decided against LED though I saw several advantages with the practical use.

Mainly the time used to build it spoke against it from my point of view. My main handicap is the time I have left beside regular work, not space not money.

So I built a box with some Sylvania tubes within a few hours.

 

[John Dean]

I'm not sure what you mean by time to build. You can now buy the LED lights in strips, which you just cut to the exact length you need which is fantastic. It allows you to build a box the exact length and width you want for any application. Also the weight, man, the weight is nothing really. And they are easily replaced. My only concern is I don't know the exposure times because I haven't talked to anyone who is actually using them, other than the silk screen people using the really big powerful units.

john

 

[thuggins]

I recently bought this off of Amazon.

https://www.amazon.com/gp/product/B01KZLM3QC/ref=oh_aui_detailpage_o09_s02?ie=UTF8&psc=1

It is very bright, even on the 20% setting (bright enough to light a room). The adjustable color temperature is a nice feature; it works very well.

I was going to make a printing "box" with it, but after thinking it thru decided that a copy stand would be better. This allows the light source to be easily raised an lowered. It will hold a camera and so function as a regular copy stand. It will also pack flat and take up less storage space than a box.

Given the brightness of the light, it will probably need a significant amount of masking, a filter, or both. A timing relay allows control down to a fraction of a second.

 

[john_s]

Having had problems making safelights with orange/red LEDs (spectrum wider than expected) I would think that white LEDs would make a very effective contact printing box! They also respond very well to simple current reduction to reduce brightness. The only problem I envisage is uniformity: lots of LEDs uniformly spaced would be my approach, and a wider array than needed for the paper to minimize edge effects.

 

[locutus]

I recently bought this off of Amazon.

https://www.amazon.com/gp/product/B01KZLM3QC/ref=oh_aui_detailpage_o09_s02?ie=UTF8&psc=1

I was looking for a lightsource for a homebuilt enlarger back for my 5x4 and this looks perfect!

 

[Tor-Einar Jarnbjo]

I have never tried, but I can think of at least two issues using LEDs as light-sources in a contact printing box:

The actual light source(s) in an LED module are very small points, whereas a fluorescent tube glows more or less uniformly from the entire surface. To ensure even illumination, you would probably need a rather sophisticated diffusor design if using LEDs as a light source.

Many alternative printing emulsions are only sensitive to ultraviolet or near-ultraviolet light (wavelengths below 400nm). Even regular fluorescent tubes emit enough energy in this area of the spectrum to cause the emulsion to react. White, high-power LEDs have almost no emission below 450nm and will probably not be able to expose most alternative emulsions. You can of course buy dedicated UV LEDs, but these are quite expensive and have a relatively low luminous flux.

 

[thuggins]

I was looking for a lightsource for a homebuilt enlarger back for my 5x4 and this looks perfect!

I originally bought it for a home made enlarger. Decided to walk before running, so the contact printer is the first step.

The actual light source(s) in an LED module are very small points, whereas a fluorescent tube glows more or less uniformly from the entire surface. To ensure even illumination, you would probably need a rather sophisticated diffusor design if using LEDs as a light source.

This panel provides very smooth, even illumination. Much more even than my lightbox, which is noticeably brighter right over the tube. I originally thought it may need a diffuser but this is pretty much the flattest illumination source I've ever seen.

 

[john_s]

My comment above can be ignored because I didn't consider the need for UV.