DIY UV LED Exposure Unit - Will this work?

[JonnyP]

I am building a new DIY single point source UV LED exposure unit.
The glass will be about 36" x 42"  -- I'm using low iron Starphire glass
Hoping to be able to place the UV LED light like 20 - 30" from the glass

For the light source, I'm thinking of using this:
http://www.topledlight.com/200w-ultra-violet-uv-395nm405nm-high-power-led-light_p1509.html

It is a 200watt, 395nm - 405nm LED, so should work with, for instance Saati PHU emulsion.
As I understand it, I need to attach it to a heat sink and a driver, both rated for this lamp.
I am no electrician, not even a little bit, so I'm a bit nervous about it.
Will it work? Will it expose the screen even at the edges of the glass?

The other option is the SAATI 300w LED light, which is a plug and play option, but it's $1000 more than this.

What do you think?

[Sbrem]

I recently built one, just like this. At 200W, you'll be more like 12" - 20". I haven't had a chance to test mine yet, (we have the Saati 450) but since I garnered my info from another forum where a bunch of folks were experimenting, I'm going with those recommendations to start. You should make a reflector too... Parts wise, including box, I was under $300.00.

Steve

[blue moon]

With the single point light source, it is all about the reflector. If it doesn’t disperse the light evenly you will have a huge hot spot in the center of the screen.
Pierre

[3Deep]

I didn't think LED gave off that much heat if any?

[Frog]

With the single point light source, it is all about the reflector. If it doesn’t disperse the light evenly you will have a huge hot spot in the center of the screen.
Pierre

Do any other members, especially  DIY'rs, perhaps have a radiometer that could be lent? A lending tool library (with adequate deposits and of course lendee-funded shipping) could be a valuable asset.

[easyrider1340]

I just built one with 50 watt LED.  I figured it had to be better than my fluorescent tubes.   Fixture is 22” from glass.  Glass is 28”x32”

Exposure times on a 156 are double my tube unit.  (About 7.5mins)
230’s are about half of my fluorescent tube unit.  (2mins)

I used existing WR-14 emulsion so I could compare apples to apples.   Coated 1:2. 

Now that I’ve got a ballpark, I’ll use PHU and do exposure tests again.


Terry
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[JonnyP]

Thanks for the discussion.
For those of you who have done this -- did you use a reflector around the edges of the LED, or perhaps extending out to the box?

For glass - any info out there on whether getting tempered glass is going to affect UV transmission?
The Starphire has very high transmission of UV and the glass store indicated that there was no difference in transmission between tempered and not tempered (obviously laminated is all about stopping UV from being transmitted, so non-laminated for the glass).

Thanks.

[Sbrem]

I didn't LED gave off that much heat if any?

Oh yes, they do. That's the reason for the heat sinks for COB LED's. Our Saatil 450 has a very large fluid heat sink. The one I built is a fin type block I bought on eBay. The LED mounts to the flat side (well, duh!) and you need a thermal adhesive, which helps draw the heat from the back of the COB into the sink. I have a 12v fan attached to the back of the heat sink. As Pierre points out, the reflector is quite important, and I believe Mr. Buffington posted eloquently about that in the last week or two.

Steve

[easyrider1340]

I haven’t incorporated an additional reflector (yet).   

Do I need one?  Current screens are 20x24.


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[blue moon]

Find/buy a meter and measure the field. I can tell you that almost every LED field I measured few years back was uneven (some from the big names in our industry). On the other side, our old MS3140 was spectacular (large area and even intensity).
With a hot spot in the center, the edges of your screen will be under exposed and will break down during the run. If the spacing between the LEDS and/or the distance from the glass is incorrect you will get spots of high intensity on the emulsion. So there might be a 30% variation in the intensity on your emulsion (think polka dots). So how do you expose for that?
The only way to know for sure is to measure it. Anybody willing to come to Cleveland, I’ll gladly take the readings and help you fine tune it.
So TLDR, measure your field! Or I would not use it.
Pierre
P.s. no, i will not lend my spectrometer out. It’s probably about $2k now and the software is registered and limited to one user.

[Frog]

P.s. no, i will not lend my spectrometer out. It’s probably about $2k now and the software is registered and limited to one user.

I was thinking of meters that are more in the $100-$200 range. Are they of no use? Ten or fifteen years ago, Chromaline was even selling one for a limited time at $50.

[easyrider1340]

Appreciate the wisdom Pierre!


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[Frog]

Find/buy a meter and measure the field. I can tell you that almost every LED field I measured few years back was uneven (some from the big names in our industry). On the other side, our old MS3140 was spectacular (large area and even intensity).
With a hot spot in the center, the edges of your screen will be under exposed and will break down during the run. If the spacing between the LEDS and/or the distance from the glass is incorrect you will get spots of high intensity on the emulsion. So there might be a 30% variation in the intensity on your emulsion (think polka dots). So how do you expose for that?
The only way to know for sure is to measure it. Anybody willing to come to Cleveland, I’ll gladly take the readings and help you fine tune it.
So TLDR, measure your field! Or I would not use it.
Pierre
P.s. no, i will not lend my spectrometer out. It’s probably about $2k now and the software is registered and limited to one user.

If one had a few Stouffer scales (or similar) could test exposures with them placed at increasing distances from the center be a good starting point?

[blue moon]

Find/buy a meter and measure the field. I can tell you that almost every LED field I measured few years back was uneven (some from the big names in our industry). On the other side, our old MS3140 was spectacular (large area and even intensity).
With a hot spot in the center, the edges of your screen will be under exposed and will break down during the run. If the spacing between the LEDS and/or the distance from the glass is incorrect you will get spots of high intensity on the emulsion. So there might be a 30% variation in the intensity on your emulsion (think polka dots). So how do you expose for that?
The only way to know for sure is to measure it. Anybody willing to come to Cleveland, I’ll gladly take the readings and help you fine tune it.
So TLDR, measure your field! Or I would not use it.
Pierre
P.s. no, i will not lend my spectrometer out. It’s probably about $2k now and the software is registered and limited to one user.

If one had a few Stouffer scales (or similar) could test exposures with them placed at increasing distances from the center be a good starting point?

Yes, that would work in a pinch. Those strips are hard to read on the photopolymer emulsions (at least the ones I tried), but are better than nothing.
Pierre

[blue moon]

P.s. no, i will not lend my spectrometer out. It’s probably about $2k now and the software is registered and limited to one user.

I was thinking of meters that are more in the $100-$200 range. Are they of no use? Ten or fifteen years ago, Chromaline was even selling one for a limited time at $50.

Problem is most meters barely register 405nm light. They are calibrated for 325-365 and are maxing out at 400-410. This is the cheap stuff I have. Between Richard and myself, we have about 5 different meters and only one is capable of measuring correctly (it provides full output graph of all light from 200 or so to about 600).  I could not find anything under $1k that would analyze low 400s.
If anybody finds something they are thinking about buying, post the link here to the specs and sensitivity graph and i’ll take a look.
Pierre