Help lower canopy is light green

unless leaves were suffocating it and shielding it, probably not from being shielded. My lower third is heavily shielded and it's all still lush. So, it's definitely not a universal reaction. Looks like 2 patterns of progression going on, too. Any paling that is progressing tip-in and bottom-up on plant is very likely a nitrogen deficiency. If this is isolated to a few of the lowest leaves, it could just be the plant shedding some leaves it doesn't need. If it progresses and gets worse, it's a nitrogen deficiency. Also looks like some interveinal chlorosis is developing -- this is different from paling tip-in and can be caused by numerous things, so you'll need to cross-reference more information to eliminate possibilities. i don't think it is a mg-deficiency because that should be accompanied with spots, too. So, numerous trace elements cause that. Make sure pH is relatively okay. IF soilless/hydro, make sure one of your products contains the trace elements and soil really shouldn't have this problem, unless poorly constituted. Molybdenum looks closest to what you have going on in first picture on right side of frame. Trace element issues are rare and more often caused by ph-caused or various nute-concentration-caused lockout. In this case it very well might be, becausae you'd usually have other symptoms coinciding under those contexts, but not always. leaf symptoms are indiscrete., they are not 1:1. you need to use more info to eliminate less likely options. Download a leaf symptom chart. download mulder's chart. these along with knowledge of your behaviours will make diagnosing easier and more accurate.

Could you update your diary with what you're feeding and have you changed the feeding lately or since you started flowering? Your diary says you're in Week 2 of flower, the latest I would do a major defoliation is Week 3 of flower. You still have time if you want to remove some and if I were you, I would definitely do it or you're going to have air flow, humidity, and possible mold issues. It's pretty thick in there and is going to get worse. I see you already have a fan at the bottom, that's good 👍

Either lack of light or lack of co2 hitting those particular leaves I wld check the run off water ph to see if you lr soil ph is off.