A micrometer (µm) is a unit of length in the metric system equal to one millionth of a meter.

A light-year is the distance that light travels in a vacuum in one Julian year (365.25 days), approximately 9.46 trillion kilometers or 5.88 trillion miles.

This is because a micrometer is an incredibly small unit, while a light-year represents an enormous distance. The number of micrometers in a light-year is astronomically large.

While a direct conversion of 1 billion micrometers to light-years results in essentially zero, understanding the relationship helps illustrate the vast differences in scale between the microscopic and the cosmic.