Is it worth moving seedlings from grow lights to sunlight?

My father, who's 82 and gardened all his life, very successfully, starts all his seedlings under grow lights. But on sunny days, he will move the tray of seedlings to a sunny spot for an hour or two, then move it to another window, etc. Then back to the grow lights when the sun is gone. Drives my mother crazy, but he enjoys fussing over them. Like I said, he's very successful, so I shouldn't question him, but I'm wondering what everyone else thinks. Is it worth the effort? Is there any benefit from the natural sun through a window?

You certainly don't need to do that, they will do fine with just the grow lights as long as you keep the lights no more than a few inches above the tops of the plants. In fact, often sun coming through a window is often not strong enough to keep the seedlings from getting leggy so grow lights usually work better. As far as your dad though, if he has good luck and it makes him happy to fuss over his seedlings like that then I would leave well enough alone, but you certainly don't need to go to all that trouble with yours.

Personally, I think it would be of benefit to the seedlings if you want to go through the trouble. They would get used to sunlight gradually, which is much stronger than grow lights. I also think it would be easier to harden the plants off when it is time to plant them out.

Plant tissue is without protection when grown under grow lights. It is a softer growth. Under the sun, plants tissue becomes tougher to be able to withstand full sun without burning.

It is the same idea as your winter skin burning under the first summer sun. Once you have a few layers of sunburn on your skin, your skin is able to withstand more sunlight without burning as much. Plants are no different.

I would agree if it were sunshine outdoors, but sunlight filtered through a window isn't nearly as strong.

Sun filtered through a greenhouse is stronger and longer than a plant grown in a sunny window in the house.

Oh, was this about greenhouses? I thought the the question was about windows in the house.

yes, it is windows in the house. I have to admit, the last time I saw my father's tomato plants, about a week ago, they were more leggy than mine are. But by planting time, his tomatoes are always beautiful and not leggy.