were they hardened off properly? seedlings look fine too me.

I bought them from lowes/home depot. So I would assume they were hardened off since they have been hanging outside in their outdoor area?

Some of them have that dried up burnt looking tips like this.

I don't think that anything really looks wrong with the big tomato. It might not have appreciated the temps down to the 40s that one night, but it will recover. If there's anything else wrong with it, it is not pronounced enough to be identified. Just let us know if anything starts to look bad.

For the seedlings, the dried up tips look like they didn't get enough water at some point. They're fine now, even the ones with the burnt tips. They just dried out sometime in the last week. If they are on a heat mat, this can accelerate the water loss from the plants if the soil medium dries out.

The fluorescents won't burn them. I often let my seedlings touch the lamps.

Just a guess about the seedlings. Sometimes when the cotyledons don't release from the seed coat cleanly quickly, the part caught inside the seed coat for a while will look like that. I wouldn't really worry too much about them as long as the brown does not spread further.

my plants are 3 weeks old from the time of seed germination and now some of the plant's cotyledons curling up and tip is turning brown. i have germinated them in coco coir and did not use any nutrient for first 10 days. please Help!!!