Or, you could do it the "old school" method of getting the light as close as possible to the plants without them showing any adverse signs like curling leaves, etc.
As indoor growers, we're fighting the "Inverse Square Law" (see your old Physics textbooks!
) which basically says that if you increase distance from the light by "X" you decrease the light intensity by X-squared. The light, as you move it away from the plants, covers a larger area but the intensity is spread over that larger area so what falls on the plants is significantly reduced.
You want that light as close to the plants as possible while still having coverage of your grow area (i.e. no shaded spots at the borders/edges).
I'm not "poo-pooing" the app which does give useful info and may show some problems with the light you're using, but ultimately, I would resort to the above before relying on the app.