The diffuser distributes the light of the three LEDs in the bottom area of the MK4/S display housing. Especially if the display protrudes over the edge of a table it is difficult to see the illumination. In my case it is attached to the Prusa Enclosure so the modification is tested with the original xLCD-support-L-MK4 and xLCD-support-R-MK4 on version B display (referring to the Enclosure assembly instructions of September 2023). I expect this to fit as well with the version A display as the left and right support parts are used for both version in the instructions.

Update according to MK4S: Without any changes the part can be used for the xLCD upgrade of the housing as well. I reused my printed light diffuser from the MK4 for the MK4S. There will be no fixture like with the old housing but it still fits well between the PCB and housing parts (see last screenshot).

Print instructions:

• 0.10mm layer height
• transparent PETG (optional white PETG for bottom layers)
• default Prusa Slicer settings with the new Input Shaper profile
• No support needed!

I used white PETG for the first three layers in order to improve the reflection of the LEDs and continued the rest with transparent PETG. 

Assembly instructions: (tested with version B xLCD at Prusa Enclosure)

• Remove the two M3 screws that mount the display to the Prusa Enclosure
• Remove the xLCD and PE cables
• Remove the two M3x8mm screws of the left and right xLCD-supports in the bottom area (LED side)
• As well loosen the third screw (not the PE faston)
• First slide the LED diffuser part under the xLCD-support-R-MK4 (left side in the pictures)
• Next insert the small diffuser fixation part in the unused hole of xLCD-support-L-MK4 and arrange it to hold the LED diffuser
• Insert and tighten all screws back to the xLCD housing
• Mount it back to the Prusa Enclosure
• Enjoy better light distribution!

Happy printing!