The seedlings can get sick, they can be damaged by pests, they can freeze after transplantation. In a nutshell, anything can happen.
All this can be foreseen and excluded. But there are non-obvious mistakes - this is when everything seems to be done correctly, but something still happens to the seedlings.
This is not the best place to grow young seedlings. Yes, there is more light here. But there are simply no other advantages. But there are more disadvantages.
Firstly, it is impossible to create comfortable temperature conditions for the growth of greenery on the windowsill due to drafts or simply cool air coming from the cold glass.
Secondly, there are usually heating radiators installed under the windowsill, which dry the air.
Thirdly, if this is a window facing north, the plants will not have enough light anyway.
The air in the room needs to be humidified, even if the seedlings are growing far from heating devices. It is not necessary to do this with humidifiers. It is enough to cover the radiators with a damp cloth or place containers of water nearby.
Having phytolamps, you need to use them correctly. You should not turn them on all day long - plants also need rest. In cloudy weather, some crops need up to 15 hours of additional lighting, others up to 12. Flowers need less - 6-8 hours.
In this case, the lamps must emit a light wave of the blue-red spectrum and be placed at a suitable height.