Different porch lights are used to mark important occasions. One of the variations is the black porch light, which signifies both events to mourn and occasions to celebrate.
Traditionally, black is known as the color most used to signal death and mourning. Some people use black light bulbs if they are in mourning as a means of expression.
Other times black light bulbs are meant to honor the deceased, express to neighbors to please be courteous outside the home, or even signify a celebration.