If the entrance is too dark, it is necessary to strengthen the sun's spirit by lighting, especially when the house is big, there are few people living and the sun's spirit is not enough.
It is also possible that the gate is located in the shade. In order to prevent the intrusion of ghosts, you can light an ever-burning lamp in the shadow to resolve it.
It is also possible that the five elements where the gate is located need fire to promote prosperity. Light belongs to fire, and the number two also belongs to fire. If the feng shui master asked for two light bulbs, that's probably why.