If we are planing to invite some travelling guest for the Purim Seuda and they may arrive after the Shekia (sunset), is the fact that they arrive and there is light in the house permit them in need to eat then as a well lighted room helps in other similar situations?

Although Poskim permit the use of light at night for certain mitzva needs such as Shechita done at night or even a court case or Get in case of need, it does not apply to regular mitzvos such as Tefila and Shema that have to be done during the proper day. Horav Shlomo Miller’s Shlit”’a opinion is that the guest should eat his Purim Seuda even for breakfast in need.