Evening mathremuk,
Different shops have different policies on refunds/exchanges especially when the items are unpacked, If you chose it in the first place, they may argue that if they were'nt the ones you wanted, why did you pick them up and buy them.
In regard to rights, they may have a sign in the shop or if they have a website that displays simply their rules on purchases and customer rights also, so worth checking out.
Were you mis-informed by the sales assistant that served you that they were the type you required?
Did you tell them that all you wanted to do was to exchange for 3 other lights?
Have you damaged the box/packaging when unpacking the items that they cant re-seal them, but then they still wont be able to sell as new, as you plugged it in and tried them.
Where are you located and whats the name of the shop? I'll look in to it, discreetly of course :0)