I realize this thread is about UV Ink Cure lights, but I found this somewhat technical article on the various ink formulations.
https://sdgmag.com/features/uv-cure-ink-technology
And now to bring the post on-topic....
Excerpt from the article:
LED curing systems generate UV light around one peak wavelength, ink formulators have had to search out and employ photoinitiators that optimally stimulate at the same exact wavelength as the one the LED curing system generates. Conversely, LED lamp manufacturers have focused on tuning their systems for wavelengths to match those that will stimulate known and readily available photoinitiators. The following light wavelengths will work with certain photoinitiators: UV-A at 365 nm, 375 nm, 385 nm and 395 nm, and into the visible light range 405 nm and at 415 nm. Ink maker INX International reports that 365 nm wavelengths cure dark colors better than 385 nm, while 385 nm cures light colors better. Equipment manufacturers may eventually include multiple LED types with sets tuned to different wavelengths to match the best chemistry for applications.
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So, to design a DIY UV array, I think you have to begin by choosing the ink, then design (or select) the UV array to match the ink formula's range of photoinitiator wavelengths.
So the basic design process would be something like:
Identify UV cure ink recommended for use with Epson inkjet printers
Based on ink cure specs, design or select an LED array that delivers the required energy, in the required wavelength ranges, during the window of time the array (i.e. print head) spends over the freshly-printed uncured ink.
Ensure the UV array operates within its recommended thermal operating range. Add cooling as needed.
Ensure the UV cure ink is kept within recommended temperature. Add cooling as needed.
Ensure UV light does NOT reach the print head nozzles by blocking it with a shield or whatever.
Ensure the additional weight of all this stuff does not impact print head ballistics, stability, accuracy, etc.
??
profit!!
p.s. I'm a total noob at DTG and UV cure inks, so please excuse if my terminology is derpy, or I'm just blithely stating obvious crap that everybody else already knows.