Nice project from Petar , he send me some photos of his UV Box. This UV LED Exposure Box was published in the magazine Emiter, and here’s what the author says on this project.
My UV box contains 54 ultraviolet 5mm LED distributed in a matrix of 9X6 leds.
The box can enlighten board with maximum dimension of 12X18cm.
Built-in digital timer allows programming of the desired time for lighting.
Keep away your lights from direct UV light from box.
Wavelength of the LED is the same with the sensitivity of the UV spectrum of photo spray Positive 20.