The cruises compared here
Day and evening cruises on the Thames are different products that happen to share a river. By day you buy transport with a guide. After dark you buy a drink, music and a view of the bridges lit up.
The choice depends less on the light than on who is coming and what you expect to learn.
1What daytime boats do better
All three daytime sightseeing cruises include live commentary in English, and two add an audio guide app in other languages. You hear which building is which. They also run all day at short intervals, so there is no single departure to miss.
They are cheap, from €16.46 to €20.23, and they refund you up to 24 hours before. Children are welcome, and the listings have separate child rates. Both operators accept dogs on a lead on sightseeing boats.
The boats have open upper decks, which is where you want to be for photographs when the weather allows.
2What the evening adds
The sunset cruise is timed to leave at sunset from April to September and at dusk from October to March. The listing highlights the Illuminated River lighting on London Bridge, Southwark Bridge and the Millennium Bridge, along with the London Eye, the Tower and Tower Bridge.
You get two hours on the water, more than any daytime ticket gives in one sitting, with a glass of prosecco, cold canapes and live jazz. There is an enclosed saloon and an open-air deck. Its score, 8.4 from 823 reviews, is the best-supported in this comparison.
3What you give up after dark
Neither evening cruise mentions any commentary. If nobody in your group knows London, you will sail past things without knowing what they are.
Age limits apply: over 16 for the sunset cruise and 13 for the dinner cruise. Both are marked as not wheelchair accessible, and both stop refunding three days before the date. Seating on the sunset cruise is unassigned and tables may be shared.
Prices jump as well, to €43.92 for the sunset cruise and €116.46 for dinner.
4Weather and season
Rain matters less than you might expect on either kind of boat. Both sightseeing operators describe enclosed lower decks alongside the open top deck, and the sunset cruise has a large enclosed saloon. The listing itself says the open-air deck suits warm spring and summer nights, which is a fair hint about the rest of the year.
Season changes the evening cruise more than the daytime one. Between October and March it leaves at dusk and most of the two hours are in darkness. From April to September it leaves at sunset, so the first part of the trip is in fading light and the bridge lighting comes later.
5A sensible way to do both
If the budget allows two trips, take the cheap Westminster to Tower Bridge cruise early in your stay for orientation, and the sunset cruise on another evening. Together they cost about half of the dinner cruise.
In winter there is a third route. From November the last Greenwich cruise leaves Westminster at 3:40 pm, when the light is already fading, so a late sightseeing boat gives you dusk on the river with commentary and children on board.