A light-year is the distance that light travels in a vacuum in one Julian year, which is equivalent to about 9.46 trillion kilometers or 5.88 trillion miles.

One light-year is approximately 9,460,730,472,580,800,000 millimeters.

This conversion is primarily for theoretical or computational purposes, to represent extremely large astronomical distances in a very small, granular unit, often for specific scientific models or software inputs.

No, converting light-years to millimeters is not a common conversion for everyday use due to the extreme difference in scale. It's mainly relevant in specialized scientific and astronomical contexts.