Light burn, light burn due to humidifier water lights?

Well, I am just following their chart ! It advises to keep feeding the BioGrow through flowering stage. Why would they do that if it's so bad?

Yes you are right! The cause is water drips on the leaf working like a magnifier in your strong led! No need to cut the leaf but keep it dry from now (at least when the led is still on). You also give too much Nitrogen (N). It still did not created a nutrient lockout or a deficiency but if you continue feeding the Bio Grow it definitely will become a problem. So stop giving the Bio Grow. It does contain too much Nitrogen (N). Your plants just passed the pre-flowering phase. They manily need p Phosphorus (P), Potassium (K) and Cal-Mag for the rest of the flowering phase. Enjoy your grow!

I appreciate the answers, if it was nut burn wouldn't it be on the newer leaves instead of some of the lower leaves?

not likely light burn. Are you getting dew on your leaves? constant standing water on the plant would be bad for several reasons but still not the cause here. i think the soil composition and watering habits are the cause. allow it to dry more between irrigations, if possible. Use more perlite or similar amendment with soil. up to about 1:1 ratio with soil will improve root zone before diminishing returns. over watering will be impossible. even if you try to irrigate a bit more frequently it'll avoid these sorts of blemishes, given common sense limitations. this would reduce water capacity of your pot, which would mean you have to irrigate a bit more often throughout the grow - similar volume of overall use but more frequent applications. It's worth it and you can always re-assess the pot size you want to use to mitigate it too. Algebra is useful stuff :P

Feed nutrients mix with O2 and your soil will get fresher avoiding lots of issues.