Illuminations Tours?

Try www.pariscityvision.com - they have a night tour by bus that includes a cruise on the Seine starting at 38€ per person. There are also tours by car - old classic Citrons - but I think they are pretty pricey. Conversely, you could do a DYI by riding the #69 bus from La Bastille to Champs de Mars, which would allow you to see much of the city along the river lit up, then top it off with a river cruise.

Any of the evening Seine cruises, as long as they are after it gets dark, will show the city lit up beautifully. Remember that Paris is quite far north, so in August it won't get dark until after 9 PM.

There are several posts on this site with info on Seine River Cruises.
We got on at the dock across the street and down the steps to the River at
the Eiffel Tower. Don't remember the name of the company (there are a bunch of them) But we wanted a night cruise to see the lights of Paris.

Bought our tickets out of the machine at the tour launch area and had to wait about 20 - 30 minutes for the next cruise - lasted an hour and we sat on the seats outside on the top deck - it was wonderful.
If you would like others' info - at the very top of the screen there is a SEARCH field and you can type in Seine River Cruise and it will search RS site and give you lots of other posts.
After dark the lights of Paris are amazing.
Be sure to sit outside on the deck benches for the best views.

We were in Paris last month. Sunset was late, around 9:30 pm, and it did not really get dark for the full effect of the city lights until well after 10 pm - more like 10:30 - 11 pm. I recall that the Seine river cruises ended before that time. I also recall that the illuminations tours begin around 9 pm - which means that during our time there much of the tour would have been in dusk, not in the dark. We just ended doing our own viewing of some of the illuminations late at night. Check the sunset schedules for the dates of your trip.

all these are good. Our way of doing illuminations is to walk around Paris at night. This past May we had drinks with friends in Place Opportune the #10 exit of the Chatelet metro and a beautiful little square. We then walked to the Hotel DeVille nearby which is simply stunning at night up close and then we walked across the river to Notre Dame, another wonderful sight. The front while lovely is nowhere near as dazzling IMHO as the back, so we crossed the bridge at the back and walked by the illuminated back of the Cathedral then across Pont Louis Phillipe which offers a great view back downriver of many illuminated central buildings, before catching a metro at Pont Marie.

Another great walk is to walk up or down the Champs Elysee to the Grand Palais and then across Pont Alexandre on the top of the hour with the Tower sparkling and then on up the Seine to Notre Dame. Paris is not huge and you can walk around a fair bit of the center easily. It is much more powerful than from a car although an open top bus would also be a good choice.