The police officer whose rubber bullet blinded 41-year-old Joachim Gatti on a protest in 2009 was handed a 15-month suspended sentence and banned from carrying arms for 18 months.
His two colleagues were declared innocent of wilful violence against two demonstrators but found guilty in the cases of two others and given suspended sentences of seven and 10 months along with a weapons ban of a year.
The injuries were inflicted at a protest against the closure of a squat in Montreuil, just outside Paris, in the evening of 8 July 2009.
Six people were reported to have been hurt and four took legal action.
The police claimed to have been met by a "shower of projectiles" but witnesses' testimony failed to back up their account, according to the prosecution.
42 injured, one dead
A man died when a Flash-ball hit his body in Marseille in 2010 and a school student was seriously injured in the eye in the same year.
Campaigners say that 42 people have been injured by the weapon, which is supposed to be used for the peaceful dispersal of crowds.
Flash-balls are used by police in France, Portugal and Macau.
France's rights ombudsman, Jacques Toubon, called for their use to be banned in 2015.
Trade unionist fined
Also on Friday a trade unionist was fined 500 euros and ordered to pay 17,000 euros costs after being found guilty of throwing paint onto the facade of the headquarters of the national building employers' association.
Although he was photographed carrying a paint gun, the 53-year-old claimed he had "confiscated" it from a fellow demonstrator.
The FFB bosses' union claimed the 40 demonstrators, who were protesting against an alleged death a day in hte industry, had put "intolerable physical pressure" on its employees in the building.