Browning of Top Stems

Im a first time grower, seeking guidance from knowledgeable peers with experience....

Zkittelz Autoflower
Week 2 from sprout
Happy Farm soil No added nutes
Mars Hydro TS1000 Grow kit

I noticed within 36 hrs ~ my girls stems are turning brown after I increased lighting from 50% to 60%. I'm 22" from top of canopy. They look healthy otherwise. Is the browning OK? Are the lights too bright? Is death imminent? Lol. Should note I done LST perhaps early AF at 2 weeks but this 1 seems to be going a bit faster than other two and I was trying to satisfy height distance for all 3 girls.

Relax.. I know the feeling starting out. Pots look a little bit big but other than that you're on point!

They are big enough to have created the first layer of stem so you're done with the most sensitive part. Should be smooth sailing from here. Keep it simple starting out. I remember just using high quality soil my first few grows and transplanted a couple of times throughout the grow in new flowering mix. I would focus on your watering technique and the amount of water in the beginning. You don't seem to be watering to much, that's good. Probably the most common problem starting out, how much water and when? I go by visual, poke and feel with my finger in the soil, check the surface of soil surface and weight of the containers.

I personally just sprinkle a little lime on my mom's when I see they start to drift in color. Low pH is very common in peat based soil, most soils come already amended with lime. I add a little maybe every other month. Good luck with your grow!

Everything looks very different each time you increase lighting levels. What looks bad sometimes in bright light looks fine in normal lighting.

Looks fine to me. Increasing the intensity of the light would result in minor stress, but nothing to worry about.