Thanks I'll check for insectsI would like to know what you are feeding your plant, as to my eye it could be a magnesium deficiency . Do you use supplements, like Cal Mag or kelp because a def in cal/mag usually shows up about that time. If the veins are yellowing, then it is a def probably, but if the spots are all over, check under the leaves at the brown spots for insects (use microscope) for insects/eggs. I think considering you only have 4 weeks approximately left until finish, you should be OK. Good luck.
This ^Maybe with the increased light the plant needs more nutes?