Try using something like this and so on this way you have a way to introduce cooldown between lightups. An alternative is using the greenfoot delay function, but that stops the whole act for a few moments

A for loop, as Kyuubi suggests, will not work here. The loop will complete its processing in one act step and all will light up immediately as a result. It would be difficult to provide decent code without seeing what you have to work with. Please provide your Lantern class code. Then, also, provide any code you have outside that class that controls (whether working or not) the lighting/darkening of the lanterns and indicate which class those codes are located in.