Mike Hulsman, thanks for the link. Very interesting information. I have gone to consider technical subtleties...:-)
But for print B&W on a multicontrast paper a bit different installation is required, I think. The additive way of the print means serial exposuring of photographic paper by three (R, G and B) LEDs. For a multicontrast paper, as I understand, it is required to mix three colours in a different proportion and to exposure once. I see a problem in mixing of colours. Small LEDs in dense packing and good "mixer" are required, I think.