too much light will never be a problem. not enough heat/cold roots. I am going to guess your plant is in a double glazed low-E window. If so your tree needs heart and light. If your window is not low-E and it faces south the black pot may be heating up to much in the bright of the day. Since this is a lemon tree we have real experts on lemons to see this and you should get good help beyond what I can offer. Any window plant should have an insulation pad under the pot.

Steve

I should note that this is my current setup in this window:

Suggestions you may have about this setup are appreciated and welcome.

It's in a very shady spot and they don't see much actual sunlight here, so I don't know that they get hot, unless my heater that I have running inside the house makes them hot?

I don't know anything of insulated or heating pads. Perhaps they are actually cold in this window? I have no clue. But I haven't really considered how temperatures may affect them before now either.

The little brown spot on the base of the petiole is normal. I seeded some lemone rosso lemons and six of them have that too. They are vigorous growing.

Excelent lighting Run lights at least 14 hours per day. I run mine for 16 hours. The trees should never sit in water so turn the tins upside down and the lift from the window sill will give them the insulation from the sill that is needed.

My small plant setup.

4 seedlings per 5 gallon bucket.bucket to right is lined with aluminum foil and has a 23 watt daylight CFL in the bottom. it goes over the aluminum foil lined extender bucket that lights the fig in an enclosed growing unit. Yout bucket could go directly over your small seedlings.

This shows a clamp light shining through a hole in a bucket lid to shine on a seedling Meiwa kumquat tree. Tree seen below.Below shows how to make a safe bucket light.One of the Meiwa trees seen above 6 months later pictured now. It is 11 months 12 days old.

Wowzers, Susanne, thank you! That makes me feel so much better.

Steve, those bucket lights look so neat! I've followed some of your other posts and always enjoy reading them. I will totally try to make one someday.

I love seeing yall's photos. I think one of the things that intimidates me most is since I've never tried growing anything before, I have no idea what things are supposed to look or what is normal! Thanks guys.

Citrus like a period of dryness before the next watering. Constant wet is not advisable.