What is the root word for lumen?

The root word for "lumen" is "lūmen", which is Latin for "light."

Here's how it breaks down:

* Lumen is a unit of luminous flux, which is a measure of the total amount of visible light emitted by a source.

* The term is derived from the Latin word "lūmen", which means "light."

So, the root word "lūmen" directly contributes to the meaning of "lumen" as a unit of measurement for light.