watch and they will let you know.
the things i look for are a bit detailed to tell you with any accuracy, i just know because i watch a LOT and take notes.
the leaves pointing up is the goal, there is a fine line between pointing up and light stress. just past stress you can see the tips turn down, yellow or brown. the reaching up becomes taco-ing.
it depends on age too. at this age the tips will turn or yellow or brown, then they will sag some.
im just guessing, but the ones taco-ing are at the edge of the light, and the droopy ones under it.
also i can tell some with mine by looking at the levels of leaves. at some point down they are happy, raise the light to make that level your canopy level. put shorter plants center and taller outter.
heat stress usually accompanies light stress and your leaves get ... hmmm... like thin and "whispy" and limp
you can grab an app to check your lux, see what it says and lower by 5k and see. you want these at/below 40k for a little while.
https://play.google.com/store/apps/details?id=com.tsang.alan.lightmeter&hl=en_US&gl=US