Single point LED....

[ABuffington]

The three main areas in evaluating exposure  light:

The histogram: What is the nanometer wavelength(s) of the light and what is the amplitude of these wavelengths?  (Olec/Douthitt puts the histogram on the box that shows these outputs, many cheap replacement lamps don't.   Question any metal halide, fluorescent, that doesn't).  This is the issue with DIY lamps.  Urban myth is just that, sometimes it works, sometimes it becomes a never ending tech call to explain this to new printers and often I use the sun as an example.  Walk outside in noon sun in the summer with an unexposed screen for 15-30 seconds.  Compare emulsion hardeness to your exposure unit that is homemade at your best time, it should be as a hard an exposure or you are short changing the exposure.  Not an emulsion fault if it isn't working, its' a light quality fault.  Multi spectral lamps do create longer lasting screens.  Single wavelength lights typical of LED energize a portion of the sensitizer, but due to proximity they are working OK.  SP1400 shot on a Starlight was equal to a 5kw metal halide in strength with a pressure washer test, but has yet to be proven on 90,000 discharge prints I find in Central America.  My feeling is it will work given that a 30 second exposure equaled a 90 second exposure on the metal halide when hit with a pressure washer test.  Try holding your pressure washer (600-1500 psi not a 5,000 psi Hydro blaster) with fan spray at 2-3 inches to see if it will blow the emulsion off during development.  The Starlight is the only one we have tested, and it worked very well with this test.  (May also give you some reason to switch emulsions as well when you see how weak some are!).


Light strength (amplitude.):  This can be a 5kw at 42 inches or a starlight at 3/4".  The milliwatt rating of the LED can be backward engineered to compare to a MH at 42-48". (See post, thanks TCT for the mind blowing graphic, if only my band would listen to me as well).

Resolution: Our tests with the starlight shows decent resolution.  Is there some undercutting?  Yes, but minimal and not enough to warrant a lower exposure time.  MH lamps and reflectors also play a huge part of the point light source resolution quality. 

Note: There are specific MH lamps for diazo, SBQ and multi spectral for dual cures.  A diazo lamp doesn't expose an SBQ emulsion as well as a diazo lamp or a dual cure multi spectral.  We recommend multispetcral for this reason.  Reflectors is a science.  Without good reflectors a light intensity meter may give different millijoule values (light energy) over the face of the screen.  I have had some units be 1/2 the strength of a dead center reading when two screens are loaded in a 2 screen system.  Disaster for WB, discahrge and HSA.  If you see breakdown on one side of a screen this is the issue.  Try shooting it dead center one at a time for MH lamps for these inks to avoid breakdown.

[TCT]

After really mulling this over I went a head and put the order in for the "300" unit. Should be in on Monday. Figured worst case scenario I return the thing. I anticipate using it horizontally with a flip vacuum frame holder I have so I can burn 2 up. I'll update you guys with progress, exposure times, pics and overall impression. I'm not DTS/CTS yet, so it will be a hands on review for us less fortunate!

[Gilligan]

Keep us poor people informed!

[IntegrityShirts]

After really mulling this over I went a head and put the order in for the "300" unit. Should be in on Monday. Figured worst case scenario I return the thing. I anticipate using it horizontally with a flip vacuum frame holder I have so I can burn 2 up. I'll update you guys with progress, exposure times, pics and overall impression. I'm not DTS/CTS yet, so it will be a hands on review for us less fortunate!

Cool! Do some testing at different EOM levels so you can determine if the LED's are powerful enough to penetrate through thicker stencils.

[Northland]

...here's a quick video of my DIY LED project, which is very similar to IntegrityShirts.
My strips are mounted on 1/8" plexi and that sits on a wood platform (for elevation).

https://www.youtube.com/watch?v=RQTXNp4U6pE&feature=youtu.be

[Gilligan]

Nice.

Any reason for your 3" off?

If you halved that distance you would increase the intensity by 4 fold according to Inverse Square Law.  As long as your light throw is still even and uniform at that distance, that is a huge gain.

[IntegrityShirts]

...here's a quick video of my DIY LED project, which is very similar to IntegrityShirts.
My strips are mounted on 1/8" plexi and that sits on a wood platform (for elevation).

https://www.youtube.com/watch?v=RQTXNp4U6pE&feature=youtu.be

Cool! I just ordered an adjustable power supply and plan to overdrive mine up to 13v or so to see if I can get times down and penetration up for thicker stencils.

The traces are so small on these cheapo leds that voltage drop is a problem even on short runs.

[ScreenFoo]

I would highly advise you research what over-voltage conditions do to LED junctions.

You are likely to increase output by a very small margin, but only for a short time before you destroy your LED's.

(Not trying to be a jerk, just hate to see a bunch of soldering go to waste )

I think Gilly is on the right track, if you want fast exposure, lots of junctions for coverage, as little distance to stencil as possible.

[IntegrityShirts]

I would highly advise you research what over-voltage conditions do to LED junctions.

You are likely to increase output by a very small margin, but only for a short time before you destroy your LED's.

(Not trying to be a jerk, just hate to see a bunch of soldering go to waste )

I think Gilly is on the right track, if you want fast exposure, lots of junctions for coverage, as little distance to stencil as possible.

The resistors along the strip limit the current to the actual LED to a certain extent. What I'm trying to do is overcome the loss due to the length of the run for the copper strip in each row of LED's

13.8V at the power supply, 13.5V measured at the ends of each strip, and 3.5V measured at each LED. 3.5V is within spec for these LED's so I think I'm ok.

[Gilligan]

I think what he's saying is that if it gets hotter (and it will) then you run the risk of shortening the life span.

I picked up some white strips for replacing some florescents as an experiment and I cranked the voltage to 13.5 and I'd say it was at LEAST 10% brighter (calculated by my highly sophisticated eyehole-o-mometer.  I put it back to 12v for now.  They are not installed yet.

[ScreenFoo]

^^Yup.  And if you go over voltage, you will run the risk of shortening the lifespan to seconds or milliseconds.

Sounds like you're on the right track how you're measuring.
If you are measuring the traces just outside the junctions themselves you have a good voltage to reference. 

If you have or can get a datasheet, check it for Vmax, IIRC it's often listed as 3.6 or 3.7
If there is an individual resistor on each you are measuring, you may be safe up to or even over 4V.

Of course, if you don't have, and can't get a datasheet, you can always destroy one to find out. 

[Gilligan]

Definitely need to feed from both sides.

I measured 9.37v on the back end of a 5 meter spool while supplying 12v to the front end.

I was disappointed by the "white" from my leds that I installed in the ceiling so I buttoned it up and went home.  When I rip them out I'll measure it and see... I may even pierce the water proofing to read what the voltage is at the halfway point.

[IntegrityShirts]

Since we are going off course here in the single point LED thread, we should keep talking over in the DIY project thread here:

http://www.theshirtboard.com/index.php/topic,12120.15.html