Tomatoes and vegetables grown under lights don't develop resistance to the sun. They need to be slowly acclimated to the outdoors for sun, wind and temperature. This is best done over a weeks time. Slowly bring the plants out for 1-2 hours, over a few days, and work their way up to full sun over the week. There is no exact recipe for acclimating your plants to the outdoors. Just don't rush it!
Even plants growing on a windowsill may need to be acclimated on a smaller scale. Plants need to adjust to wind and temperature too and windowsills don't always provide full intense sun. Better to error on caution.
If you don't acclimate your indoor seedlings to the sun, they will most likely suffer from sunscald. Sunscald is the burning out of chlorophyll and greenery on your plant's leaves. You will see lightened whitish patches on them. It almost looks like the leaves were bleached. A light burn is okay, a severe burn could kill your transplants.
This video covers some keys for acclimating your plants to the outdoors and it shows you several cases of tomato leaf sunscald.
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