Red is good. That won't bother their night vision or sleeping... I only ask because constant, white light can cause pecking and aggression.
Since the tips of the feathers are missing, I'm going to blame someone in the flock. I've never heard of worms causing feather loss like that, especially since you feel her weight is okay. A chicken with worms is lethargic, thin, pale in the comb/wattles, and usually has runny, watery poops and a poopy butt.
What type of feed are they getting and what is the protein %?
MrsB