react to how the plant grows. too stretchy, needs more light... too tight, needs a bit less. resulting node spacing is a good guide.
using a klux app or even one tha tconverts it to PPF is useful, but you can't use it in a top-down way. The amount of light you need to give depends on the environment you provide too. So, it's a bit different for everyone and genetics play a role too. So you can't just blindly apply a certain level of light based on a schedule unless you have become familiar through consistency... a learning curve.
So, use a light meter of some sort, but stick to observe and reacting to growth pattern, initially. Take readings when it's dialed in. You can skip the trial and error next time. You don't work top-down from ppf or kLux.. allow the plant to dictate what is correct... this will give you light intensity targets properly callibrated for the environment you provide.