Trying to understand formulas for lighting please send help.

I found a comment on Flytrap Care Forums with a breakdown of lighting and how it's measured and whatnot. https://www.flytrapcare.com/phpBB3/how-much-light-do-you-really-need-t31035.html

It was going great and I was making sense of things until the last bit about determining how close the lights should be from the plants. It starts out with two formulas for determining mounting distance, which is all well and good, but the example he writes out throws me off so bad. It doesn't seem like an example for the formulas at all. If someone could provide another example I would be ever so grateful.