Before You Went LED, What Were You Using?

[ebscreen]

Clustering different wavelength leds would also add to inconsistent coverage. They can't all physically exist in the same space,
so you'd have offsets from each wavelength. Could you imagine a large coverage halftone pattern where only every quarter of a square
inch on screen is receiving the correct crosslinking wavelength? And you thought moire was bad. Cringe.

You could likely increase the distance from the source until it all evened out but then you'd be back at square one.

[blue moon]

So forgive me if this is a stupid question, but wouldn't an easy solution be to create groups of 3-4 LEDs, each producing a different wavelength, and lay those out in strips?  Would this not emulate the multi-spectral properties of a MH?

it would, but at the expense of the total power at required frequency. If you split it across four different wavelengths, the usable power could be as low as one quarter of the rated power.

pierre

...Unless we get the screen 4 times closer.

actually you would also have to have all the different color LEDs bunched together at a single point or you'd have gaps in the field. So there is more to it than one line I posted.
There is already a multispectrum LED unit on the market. I've talked to the designer, but had not had the chance to test. Reallity is, without a UV spectrum radiometer it is hard to analyze what's going on. I have been looking into getting or renting one, but who knows when I'll have the time to do it. . .

pierre

EDIT: eb beat me to it!

[ScreenFoo]

Actually, you wouldn't have to worry about that if the light geometry was correct--even if the different wavelength LEDs/junctions were offset from each other by half the distance between the first junctions, as long as all the junctions of the same type provide an even pattern of collimated light, I couldn't see there being issues.

But--four times the LEDs, four times the power, four times the heat, and a pretty serious price increase.

[ABuffington]

LED is here to stay.  As much as I like MH units for there long run durability, we simply rarely see the 90k runs of discharge or HSA here in the states.  So for almost 99% of the US printers with shorter run lengths, LED works just fine.  Thanks Pierre for reminding me that the inverse square law does help with strength for LED's.  And as pointed out select an emulsion that matches the nm output of your lamp. In almost all cases if there is any SBQ, post exposing in the sun helps complete the exposure and aids in reclaiming.

[IntegrityShirts]

3 wavelengths out of one LED is possible. The adhesive LED strips that most of these units are using have the 5050 type LED in them. EACH 5mm LED has 3 diodes in it that emit light. The only problem is LED's of different wavelengths have different power requirements so you'd have to isolate each diode and supply it independently. If you look at pics of a 5050 led strip you'll see current-limiting resistors between each LED.

My opinion was summarized already previously but it boils down to light penetration or "strength". SOME LED's don't emit enough light to penetrate thick emulsions in a timely manner. The M&R unit, based on what I've read here from reviews/opinions and exposure tests, uses MUCH more current than other models (which in my opinion equates to higher quality LED components). It generates a lot of HEAT. That should be one clue that it's a bright mofo.

If anything comes of this discussion, I'd hope the manufacturers will take notice of the large variation in results from end users. It would be in their best interest to post tangible and repeatable test results for their units using specific emulsions, specific mesh counts, and specific EOM coating (not just saying we coated with a round edge 1/1 etc.).

[GraphicDisorder]

LED will end up being cheap in a few years and people will not be using MH units unless they are dinosaurs I suspect.

[ZooCity]

Great conversation.

I think it all circles back to LEDs creating the need to match emulsions to spectral output.  This has been done for special uses in the past but not generally speaking.  Alan or someone with better knowledge could clarify for me. 

The best thing I can see happening at this point is the industry settling on a standard wavelength or, at the least, a set of them.  It would limit certain uses but really fine tune the bulk of the work being done in our industry with screen imaging.  It would also level things out and allow buyers to compare apples to apples on exposure units and their outputs.  Some shops would be ok with less expensive models with less output with others shelling out for the big gun units, but at least it would all be spectrally matched and nobody would be experiencing screen failures, just differences in exposure speeds and resolution quality basically. 

[ebscreen]

LED will end up being cheap in a few years and people will not be using MH units unless they are dinosaurs I suspect.

Nothing to do with price, everything to do with fully cross-linking screens while retaining detail. It ain't there yet.

[244]

LED will end up being cheap in a few years and people will not be using MH units unless they are dinosaurs I suspect.

Nothing to do with price, everything to do with fully cross-linking screens while retaining detail. It ain't there yet.

Sorry to disagree but I think its more than there. Have you played with one of ours?

[ebscreen]

I have not, but the emulsion manufacturer that brought this back up has, and the dance he's describing
to obtain quality screens doesn't sound very fun. Using only diazo emulsion, I don't know that
we'd save any time over our current setup either, so all in all, a net loss. So far.

Anyone have any 5K or higher MH units for sale?

[GraphicDisorder]

LED will end up being cheap in a few years and people will not be using MH units unless they are dinosaurs I suspect.

Nothing to do with price, everything to do with fully cross-linking screens while retaining detail. It ain't there yet.

The context of my post wasn't about today's price. I did clearly say end up being cheap.  Which yes doesn't have anything to do with price today, correct. My point was in a few years when LED's are super cheap and the price on these units go down nobody is going to buy a MH anymore in the typical shop.

[ABuffington]

As I mentioned in a previous post, 99% of the printing you will do in the US can be done very well with the LED.  The fine tuning process has one major advantage.  It is consistent.  The main drawback of MH is shooting with a bulb that is way past it's prime and has lost a lot of the punch it once had.  If the client is still using seconds instead of light units the break down issue is huge with poor UV light and exposure will be inconsistent.  The longevity of the lamps in LED and the consistency is a great sales point.  Both camps have valid arguments.  If I was a small to medium shop I'd fine tune my emulsion and coating techniques to use an LED.  If I was a 20-40 auto shop with tons of long print runs, lots of discharge and HSA I would go w 2 MH units for multiple screen shots at one time.  Check out my previous post on how to set up a coating/exposure test for LED.  I use this technique all the time.  1 screen, 3 different coating techniques, evaluated at 3 different exposure times.  Takes all of 15 minutes to do this and will answer a lot of questions on how much to coat and how much time for a strong exposure.

[ebscreen]

LED will end up being cheap in a few years and people will not be using MH units unless they are dinosaurs I suspect.

Nothing to do with price, everything to do with fully cross-linking screens while retaining detail. It ain't there yet.

The context of my post wasn't about today's price. I did clearly say end up being cheap.  Which yes doesn't have anything to do with price today, correct. My point was in a few years when LED's are super cheap and the price on these units go down nobody is going to buy a MH anymore in the typical shop.

Which means you are clearly misreading my post. Doesn't matter if it cost twenty thousand dollars or twenty thousand pennies, if it
doesn't do what we need it to do I ain't a buyin'.

We print a helluva lot more than plastisol on Gildans.

[Dottonedan]

He's gotta be in the elite group. He might need more than the majority.


Better image quality than your every day award winner.


Maybe the 2% dots on 85lpi type and he doesn't need it to be fast.


same screens to last an entire production run of 20-50k orders on average. Give or take 10k.


It's possible and if so, more power to him and good for him.

[ebscreen]

Was that meant for a PM?