As Finnair Plus Platinum/Gold/Silver member, can I take one bag free of charge when travelling with a Light ticket?

Yes, Finnair Plus Platinum, Gold and Silver members and oneworld Emerald and Sapphire members can always take at least one checked baggage. In addition, Finnair Plus Gold and Platinum members are allowed to take a set of golf, ski or diving equipment on flights operated and marketed by Finnair.