The lighs on my new Motorola / Arris Surfboard SB6141 Cable Modem are REALLY BRIGHT! I designed this cover to slide on the front and have the same form factor as the body itself. I still wanted to see the lights (but much much dimmer), so I used white filament (ABS), 100% infill, and made it 2mm thick. In complete darkness, I can see still the activity light flashing, and the send/receive lights VERY FAINTLY. I've attached the (quickly thrown together) openSCAD file in case anyone wants to mess with it. Print it thicker or in black if you don't want to see the lights at all at night. I'm assuming this would also work with the SB6121. The SB6183 appears to be slightly wider, so would need some tweaks.EDIT: user Zen1 reports (see comments) scaling the width to 116% fits the SB6183