DIY LED Exposure Unit

I think loosing nearly 40% of your available uv is fairly problematic. If we could 'reclaim' that amount of light then the mid sized shops could all get by without spending what amounts to the price of a good Manual press on what is effectively a light bulb in a box. I know that this 'everyday' print shop would think so. I for one have more than enough invested in 'ancillary' equipment.

The whole point of the paragraph that you quoted was that there must be a way of gaining good positive contact without the use of glass. The new generation of direct to screen systems cuts out the exposure unit by printing the image directly to the emulsion.
Surely then there is a way to get a similar, low-cost effect by getting transparencies to adhere (temporarily) directly to the screen.

I've tried using 'window cling' vinyl printed on the versacamm, but it is not thick enough to get completely smooth and the vinyl doesn't have enough static cling to stick to the rough emulsion. But I think that I am heading in the right direction.
All the problem needs is a transparency film with a low tack temporary backing to stick directly to the screen. Simple, affordable and advantageous.
Maybe I should get down to the patent office?

There are other sectors of our industry that could provide us with a solution. The transfer or printable vinyl sectors should be able to develop the film, and uv conveyor dryers used by the rigid substrate and wide format solvent sector could be easily modified for exposure purposes.
All this nonsense of messing around with sheets of glass or having something the size of a deep freeze in the corner need to be a thing of the past.
After all, the only real requirement is a bit of light.

That's true - but almost all units come with low iron glass and are not loosing 40% uv. What I'm trying to say is how fast so you really need to expose? 3 minutes? 1 minute? 15 seconds? that's what people are getting and in the relative scheme of things with metal halide bulbs, the exposure time is now mostly insignificant. Metal halide is still expensive because it is relatively new to our industry. But you can still build one for cheap yourself if you want. The size of the unit is simply a factor of the light spread. Those big units you refer to allow 2 screens to be exposed at once. 1 screen every 7.5 seconds is way quicker than I can handle - the bottleneck just isn't at exposure and I don't think glass is a problem or limiting factor. Technically, I know that it could be better, but I loose way more resolution from my print method and substrate (using poly screens and printing onto cotton fabric), than I do by having the light pass through a sheet of low iron glass.

I applaud you for looking for a different way of getting positive contact, but given that the glass isn't a problem, why not just use that since it's there?

My patent actually eliminates the big exposure units and glass so please don't think that I don't want to improve the current process. But even if you came up with a better way to get positive contact, I can almost guarantee that industry will not jump at the idea. I introduced insulated concrete swimming pools to the industry in the UK. They saved 80% of heating costs, yet they were not adopted by the industry because people like to do things the way they always have. That's why people still buy wooden screens. I mean, why on earth would you buy wooden screens? But people do because they are cheap and do the job.

Unless you have a revolutionary idea that gives a huge host of benefits (cough cough, like my patent idea ), then I think that perhaps you have actually just created a screen positive contact problem by not wanting to use glass

However, if you can figure out a glass less option then it would certainly benefit the hobby market immediately and may eventually come through to the pro end. The light would need to be above, rather than below, though, because right now the glass allows me to use a variety of screen sizes without having to have a special adjustable frame to support them.

I have two problems with current exposure systems.
Firstly I use 84" screens for the correx sign printing half of my business so exposure units are large.
Secondly my old exposure unit went 'tits up' a year ago and I don't currently want to re-invest in large unit, given the changes that are afoot regarding uv led light source. When the tech settles down I may take a different view.

I have been forced, but not too reluctantly to revert to overhead lamps, which is probably where my biggest issue with the glass comes from - hefting a 7 foot sheet is not easy. I can expose 4 31" screens at a time.
The actual light source is fine and I have no issues with the exposure time (it is just long enough to burn the next screen whilst washing the previous one out). The multi point light source I have been using is not a problem for the big screens as they don't tend to use halftones. When burning 31" screens the light source is lower and each screen is far enough apart to have its own light.

Its just that the glass seems soo superfluous. I am not even talking about technological advances here, just some sticky transparency film.

Sorry to bgtshirts for hijacking your thread..

With the proper light and SBQ emulsion you can get a 10-30 sec exposure. After talking to a few of the DTS people they have had to change back to pure photopolymer or diazo due to too fast of exposure. Yes according to them there is. It is recommended that nothing faster than 10 sec exposure. There is a shop I visited that has DTS and using diazo and a Nuarc 3140 DTS exposure unit. 18-24 sec as they use light units so it varies to what the sensor reads. They were even having issues with photopolymer. With their volume its no problem to go through a 5 gal of diazo in a month and probably much more. I personally will buy 4-5 1gal containers of emulsion at a time to save on cost. Unopened a most photopolymer have a 2 year shelf life and opened a 1year. Diazo 30-90 days. Yes it can be extended longer buy personally I don't want to guess will it work today or not. The other thing is I use a registration system. With a adhesive the carrier sheets would get ruined. I have kicked around picking up a 24" epson and trying to make a poor mans DTS. The info isn't as available for the 24" as the 17" and under epson printers.

I have used standard glass which came with my old national exposure unit that I converted to metal halide. Then switched out to starfire glass which is the lowest iron most optically clear glass available. There are other copy cat glass similar but this is a PPG product and our local glass company has a display with some of the off brand, standard and the starfire. Visually there is a night and day difference but not so much when it comes to exposure time.

This next statement is more of my opinion from using the 2 different glass. I don't think the iron cuts the amount of UV that gets to the screen as much is it causes light to refract around the iron. I get slightly cleaner exposure with the low iron glass and 10-30 sec faster exposure depending on the mesh and stencil thickness used.

As some know here I do a lot of testing to prove or disprove what is said in this industry. I do this because I personally have found that some stuff being told in the industry doesn't apply to every shop.