Sorry Lars, I have no idea and no ready way of finding out. But if the Lumejet people are reading this thread, perhaps they may have a fix on it and would respond.
Hi - I'm sorry I'm late to this, but I run L-Type (LumeJet), so let me do my best.
My understanding is that the Durst Lambda was originally conceived and built as a 200ppi printer (it's before my time) and, with its 50" width, was really aimed at large prints that would be viewed at a distance. It was then upgraded to give a resampled 400dpi so that it could produce smaller prints that would be viewed in the hand. So my understanding is that 200ppi is the native print resolution and 400ppi is a resampled print resolution. We do not think there was any hardware modification to go from 200ppi to 400ppi (ie no refocussing of the beams to produce a smaller spot size) - it was a question of using the same hardware to print the extra pixels in between the ones that would have been printed at 200ppi. The result of this resampling is that the image is softer (because it every other pixel is effectively a pixel that is created by interpolation from the actual image pixels all around it). By just imaging a higher res (blended) file with the same lower res laser, you get a blurring effect at high contrast edges e.g. text and fine lines, due to the intermediate grey pixels between the black and white edges.
Our printer, by contrast, is designed from the beginning to print with a precisely focussed, sharp-edged pixel at a native 400ppi and each image pixel is, natively, printed 1-for-1 at at that resolution. Of course, if you start with an image that is only set at 200ppi, or try to print an image that is, say, 2000px over 10", then we will resample that up to give 400 print pixels for 200 image pixels.
Put differently, my understanding is that if you wanted to print 2000px on a Lambda, this would naturally cover 10" at 200ppi. If you wanted it to cover 10" at 400 ppi, then you'd resample and create the intervening pixels and then print them all with a 'soft-edged' laser dot that was designed to print at 200ppi, but is now printing on a 400ppi pitch.
If you wanted to print the same 2000px on our printer it would naturally print at 5" wide at 400ppi. If you wanted to print it over 10" then we would also need to resample, but each resultant image pixel would be printed by a very precisely formed hard-edged pixel on the paper, rather than the soft-edged laser dot. So although our image would also be slightly softer due to the resampling, it would be much crisper and sharper than the Lambda version. And, most importantly, out printer images the paper using multi-parallel beams hitting the paper vertically at 400ppi at all points of the print with virtually zero sideways pixel overlap to maintain edge sharpness. Of course if someone sends us a res’d up file we will still have a somewhat softer edge, but imaged with a hard dot – not the other way around as with the Lambda. Also, laser systems use long path lengths (several meters), spinners, mirrors, Ftheta lens (not flat across the whole bed) and 3 beams for RGB – each of which will have some chromatic aberration (different paths for different wavelengths).
I was not involved with the company before late 2015, but I believe that in 2009, Durst held discussions with LumeJet about replacing its print heads with the LumeJet 400ppi print head (as did at least one other major manufacturer). In the end, Durst pulled out of printer manufacture and switched entirely to inkjet, and the other manufacturer went bust. And at that point, development of silver halide printing by anyone other than us pretty much stopped.