There is a neighborhood called Ryan Place that usually has pretty lights, it is off of 8th Avenue and Elizabeth Avenue. Go East on Elizabeth Avenue to get into the neighborhood.
There is also an area on the West Side of Fort Worth that can be reached via 183/Southwest Boulevard. There is a stoplight at Overhill just a bit north of Vickery. Again, go east, turn right if you are coming off of 820 and turn left if you are traveling south on 183. The street Ts, turn to the right and follow it around. There is a small lake and they usually have beautiful displays with all of the houses and it is an affluent neighborhood so you are likely to see more lights if you drive through the neighborhood.
If you haven't bought one, they are a bit expensive but go to Wal-Mart and invest the I think $35. It shows to date, every street in Fort Worth, Arlington, etc. It is invaluable. I have been here since 1984 and still use it even with the yahoo maps.
If I have totally confused you, e-mail me and I will try to explain these two neighborhoods a bit better.
I haven't been yet, but downtown likely is lovely too, and the museum district which is off of Camp Bowie and Montgomery. Another thing to check out is the neighborhood to the West and East of University. Colonial Parkway, which is the street the zoo is on, that area on both sides of University has expensive homes and likely the lights to go with them, particularly the properties on Colonial Drive.