Author Topic: DIY LED Exposure Unit  (Read 6298 times)

Offline Maxie

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Re: DIY LED Exposure Unit
« Reply #30 on: January 22, 2019, 02:33:11 PM »
The theory of a point light source seems to have been thrown out the window.
Not only are people using banks of LEDs but also have the screen moving over the LEDs.
I would like to know if anyone has tested exposure with a bank of LEDs opposed to a MH.
I’d also like to see a test of static leads and LEDs with a moving screen.
Maxie Garb.
T Max Designs.
Silk Screen Printers
www.tmax.co.il


Offline ABuffington

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Re: DIY LED Exposure Unit
« Reply #31 on: January 22, 2019, 06:53:17 PM »
Hello Maxie, MH was never broken, and LED didn't fix it, LED is just an alternative system to an already great light source in MH.  MH does have some quirks that LED did help out, like lamp costs, electrical draw (which I can argue the savings are lost on your first breakdown), but are they equal in terms of exposure quality?  We have done head to head tests to help develop new emulsions for both.   LED=fast and inexpensive to operate and often the best emulsion is a diazo or pure photopolymer emulsion while dual cure tells another story.  MH = the standard by which resolution and stencil strength are judged by can expose diazo, pure photopolymers, and dual cure emulsions (perfectly).  Science tells the story.  Histograms (Spectral Output), amplitude of light, how parallel are the light rays?, all tell different stories when compared.  A lot of these annoying science facts make a difference in durability and resolution.  However the two systems can work together beautifully.  One takes care of the majority of work, but the other fixes what the first can't do. I would have both, I like LED for speed, I like MH for resolution and stencil durability, especially on thick stencils.  I work with many shops that utilize both constantly.  MH serves as a good back up to the sun on a rainy day (probably not an issue for you!) when post exposure after LED may be necessary for a high solid acrylic base destined for a long run.  In any event, you can't go wrong with either, some issues that may not be important to one shop really shows up in another.  Some print mostly spot, some 85 line concert shirts.  To each his own, nothing wrong with either system if you like the prints and your customers are stoked.  Just print.
Alan Buffington
Murakami Screen USA  - Technical Support and Sales
www.murakamiscreen.com

Offline Maxie

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Re: DIY LED Exposure Unit
« Reply #32 on: January 23, 2019, 02:48:21 AM »
Alan, thanks for the reply.     I'd guess that most people on TSB are going to have one system only.      In theory there is no doubt that a point light source is better.     How much does this effect us in practice?       As you mention, for most the LED will work fine.       
I think a good compromise is something like the Saati lamp mentioned, it's closer to a point light source and LED.
I'd like to see someone post a test chart exposed with  LED and MH?       Maybe you can post one of your tests.   
Maxie Garb.
T Max Designs.
Silk Screen Printers
www.tmax.co.il

Offline Sbrem

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Re: DIY LED Exposure Unit
« Reply #33 on: January 23, 2019, 09:38:12 AM »
to throw my 2 cents in, the point source will make better halftones, I went from Carbon Arc (really the best, but poisonous) to Metal Halide, and we are now using the Saati, still testing exposure times. We don't do very much discharge or water base, so haven't had to consider the post exposure yet. However, as Alan mentions, we're keeping the MH for just that purpose when needed, or if the LED fails. I'm also making (as a pure hobby, not as a need) lamp using a 200w UV LED, I have all the parts, except for a case, which seems to be the hard part for my needed dimensions. If I get that to work out, it could become my backup, maybe redesigned a bit, say, with 2 200w, or 4 100w. I personally have never warmed to the bed of lights idea.

Steve
I made a mistake once; I thought I was wrong about something; I wasn't

Offline Gargoyle1212

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Re: DIY LED Exposure Unit
« Reply #34 on: February 16, 2019, 01:46:54 PM »
I dont see any examples of what LED stripes you used.  Can you share a link?

I have seen problems after 1 year with LED's that had weatherproofing added.  They are duller as have yellowed.

What spectrum did you use?  I have seen 365nm which I think is to low.  I think the optimal is 390-405nm.

Offline Pangea

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Re: DIY LED Exposure Unit
« Reply #35 on: February 16, 2019, 04:44:35 PM »
Got them on Amazon, the densest configuration they had (around 3/in if I remember correctly). No need for weatherproofed type and 395-405nm is optimal for based on emulsion tech sheets I read.