Poinsettias like and need a lot of sunlight to bloom and to thrive properly.
Your poinsettias need around 8 to 12 hours of sunlight per day to be able to bloom and thrive and if you cannot get at least 8 hours of sunlight to your Poinsettias then you should use some grow lights over the poinsettias to allow them to get the needed light.
If possible place the poinsettias near a window that gets a lot of sunlight which is best for them but during cloudy days or during the winter when the weather is not very sunny then you may need to use some LED lights or grow lights for the poinsettias.
I have some led grow lights that I use on my poinsettias when it's cloudy out or when the weather is not very sunny such as on cold cloudy days.